The2004 Classification Quantification Microstructures Steels

Materials perspectiveClassi cation and quanti cation ofmicrostructures in steelsG Thewlis

The International Institute of Welding (IIW) microstructure classi cation scheme for ferrous weld metals has beeninvestigated as a basis for the quanti cation of complex microstructures in steels The aim has been to cover the fullrange of microstructures observed in plain carbon and low alloy steel products as well as ferritic weld metals andparent plate heat affected zones The mechanisms of formation of the principal structures and the characteristicferrite morphologies produced in the reconstructive and displacive transformation regimes of ferrous materials havebeen brie y reviewed The classi cation and terminology used for intragranular as well as austenite grain boundarymicrostructural constituents have been considered and also the way in which transformation products are orientatedin space Problems encountered in relating microstructural constituents to principal structures have been discussedin detail and solutions proposed The microstructure classi cation and terminology used in the IIW scheme havebeen built upon and new terminology incorporated into a table providing descriptions of the principal structures andsub-category components A new classi cation scheme has been de ned in the form of ow charts with guidelines foridentifying the principal structures Evaluation exercises have been carried out with the new scheme These haveshown that a reasonable degree of consistency may be obtained between operators in identifying primary ferritepearlite martensite and the transformation products constituting ferrite sideplate and acicular ferrite structuresnotably Widmanstatten ferrite and bainite A means is thus provided of obtaining database information fordeveloping microstructure ndash property relationships or generating data for calibrating physical models which havethe principal structures as their output MST5675

Keywords Steel microstructures Low alloy steels Ferrite Bainite Martensite Metallography Microstructure classi cationPhase transformation products

The author is with Corus Research Development and Technology Swinden Technology Centre Moorgate RotherhamS60 3AR UK (grahamthewliscorusgroupcom) Manuscript received 17 October 2002 accepted 22 September 2003 2004 IoM Communications Ltd Published by Maney for the Institute of Materials Minerals and Mining

Introduction

With the advances in computer power in recent years therehas been increasing interest in the development of modelsto predict the microstructure of steel products particularlythose processed by thermomechanical treatments1 ndash 4 orfabricated by welding5 ndash 1 1 The driving force for much ofthe modelling work has been the need for computer basedsystems to control and optimise microstructure and mecha-nical properties Linear regression analysis on large data-bases of information has proved a useful tool in generatingcompositionndash structurendash propertyrelationshipsMore recentlyneural network techniques9 have enabled prediction of situ-ations too complex for simple analytical models or multipleregression techniques Regression and neural networkmodels often nd use as online models for process controlHowever they are restricted to well de ned data over limitedranges of composition and process parameters Such con-straints can to a large extent be circumvented by thedevelopment of physical models based on fundamentalmetallurgical principles The major advantage of physicalmodels is their general applicability They can be used asdesign tools for a wide variety of new materials and pro-ducts Classical nucleation and growth theory may forexample be used to predict the microstructure of steelsprocessed to a given austenite grain size and cooled atdifferent rates through the austenite to ferrite transforma-tion temperature range4 6 ndash 8 The transformation sequenceduring cooling and the phase proportions of allotrio-morphic ferrite pearlite Widmanstatten ferrite bainite andmartensite may be the outputs The latter are the principal

structures in the reconstructive (diffusion controlled withslow rates of reaction) and displacive (shear dominated withrapid rates of reaction) transformation regimes of contin-uous cooling transformation (CCT) diagrams1 2 1 3

While the development of regression and neural networkmodels requires good quality database information thedevelopment of sophisticated physical models for micro-structure prediction in steels has led to a need for accuratecalibration data However the microstructures observed insteel products are complex A variety of reaction productsmay form at austenite grain boundary sites in thermo-mechanically processed or heat treated steels In the fusionzone of welds the simultaneous and competitive formationof a variety of phases from both austenite grain boundaryand intragranular sites may occur while in the parent plateheat affected zone (HAZ) steep thermal gradients may giverise to a wide range of transformationproducts A scheme isthus required for classifying and quantifying complex steelmicrostructures

Classifying and quantifying the microstructures of steelshas long been a contentious issue1 4 ndash 1 8 Depending on theplane of observation constituents that are part of the sameprincipal structure may appear morphologically differentgiving rise to sub-category components Furthermoresome structures may have similar morphological or genericfeatures but be mechanistically different A scheme foridentifying the various ferrite morphologies in isothermallytransformed steels was rst used by Dube et al1 7 and laterextended by Aaronson1 8 However the effect of continuouscooling was to render the distinguishing morphologicalfeatures much less distinct Allotriomorphic ferrite mor-phologies were readily identi ed and also various sideplate

DOI 101179026708304225010325 Materials Science and Technology February 2004 Vol 20 143

morphologies (often classed as bainite) Widmanstattenferrite was dif cult to place but was regarded as a genericallysimilar structure to bainite Intragranularcomponent phasessuch as acicular ferrite posed a much greater degree ofdif culty Much effort was made by the welding fraternity inthe 1980s to develop an overallmicrostructurequanti cationscheme for weld metals incorporating both prior austenitegrain boundary and intragranular nucleated constituentsand addressing stereological effects ie the way constituentsare orientated in space1 9 20 A scheme was devised whichbecame recognised as the International Institute of Welding(IIW) classi cation1 9 Most of the constituents de ned in theIIW scheme were relatively easily identi ed Furthermorethe scheme could just as readily be applied to steels whereaustenite grain boundary transformations dominate as toweld metals where intragranulartransformationsare the ruleHowever identi cation of the actual transformation pro-ducts constituting component structures such as ferritesideplate and acicular ferrite has proved dif cult Anelliand Di Nunzio2 1 recently devised a scheme providingguidance on identifying transformation products associatedwith sideplate structures which has had some success butstereological effects and intragranular constituents were nottreated in depth

The objective in the current work has therefore been toinvestigate the IIW microstructure classi cation scheme as abasis for quanti cation of complex microstructures in steelsThe overall aim has been to develop a scheme that althoughrequiring a basic knowledge as to the mechanism of for-mation of the principal structures will be relatively easy touse given optical microscopy standard specimen polishingand etching techniques and appropriate guidance Theapproach has been to review microstructural constituentsin the IIW scheme in the context of the development ofprincipal structures found in the reconstructive and dis-placive transformation regimes of steels Detailed intragra-nular as well as austenite grain boundary transformationproducts have been considered and also stereological effectsProblems relating microstructural constituents to principalstructures in the IIW scheme have been investigatedtogether with possible solutions so that a new quanti cationscheme may be developed with a much broader applicationrange The intention has been to cover microstructuresobserved in carbon (up to abount 08) and low alloy (up toapproximately 5) steels as well as weld metals (up to010C and 5 alloy) and weld HAZs

Classi cation of microstructures andterminology

In this section the mechanisms of formation of the principalstructures and the characteristic ferrite morphologies pro-duced in the reconstructive and displacive transformationregimes of ferrous materials are brie y reviewed Theclassi cation and terminology used in the IIW scheme aredescribed together with that of Dube et al1 7 to provide alink with the early work on classi cation of prior austenitegrain boundary ferrite morphologies Terminology used inrecent work by the present author and co-workers2 2 is alsoincluded to provide a contemporary view of complex intra-granular transformations including those generating themicrostructure commonly known as acicular ferrite

RECONSTRUCTIVE TRANSFORMATIONREGIMEIn the high temperature reconstructive transformationregime a change from the austenite to ferrite crystal struc-ture occurs by a reconstructionprocess involving movementof atoms across the ca transformationinterfaceThe principal

phases are ferrite and pearlite Reactions tend to bediffusion controlled with slow rates

FerriteIn low hardenability materials the rst phase usuallyforming on prior austenite grain boundaries during coolingbelow the Ae3 temperature is classically referred to asallotriomorphic ferrite as shown schematically in Fig 1The ferrite nuclei have a Kurdjumovndash Sachs (K ndash S) orien-tation relationship with one austenite grain and grow intothe adjacent austenite grain with which they should normallyhave a random orientation relationship2 3 At some lowertemperature ferrite may begin to nucleate on inclusionsinside the austenite grains2 2 2 4 and this is termed idiomor-phic ferrite (see Fig 1) The indications are that ferriteidiomorphs do not have a xed orientation relationshipwith the matrix grains into which they grow2 5

Growth at reconstructive transformation temperaturestends to be controlled by substitutional element diffusionaway from the ca interface at low undercooling and carbondiffusion at high undercooling Various growth modesare recognised in order of decreasing transformationtemperature2 6

(i) local equilibrium with bulk partition of substitu-tion alloying elements (PLE)

(ii) local equilibrium with negligible partition of sub-stitutional alloying elements (NPLE)

(iii) paraequilibrium where only the interstitial carbonatoms diffuse

The diffusion rate of carbon in austenite may be manyorders of magnitude greater than that of substitutionalatoms at reconstructive transformation temperatures Trueequilibrium segregation during phase transformations atmigrating interfaces is therefore unlikely to be achieved withregard to all components Growth under diffusion controlwith local equilibrium at the interface is then envisagedTwo phases may differ either signi cantly (PLE) ornegligibly (NPLE) in terms of substitutional alloy contentElement concentration or depletion spikes are invoked tosatisfy the thermodynamic constraints In many cases asthe transformation temperature is decreased the relativerates at which elements are able to diffuse negate theassumption of local equilibrium since the interface com-position spike would be only several atomic layers thick Insuch cases the concept of paraequilibrium is applied iethere is no redistribution of iron or substitution atoms at theinterface between the phases and only the interstitial carbonatoms diffuse The different growth modes described abovemay result in signi cant changes in ferrite growth mor-phology from equiax grains towards a plate shape (seebelow)

Dube et al1 7 refer to prior austenite grain boundaryallotriomorphic ferrite as GBF The IIW classi cationscheme refers to the rst phase forming at reconstructivetransformation temperatures as primary ferrite termed PF

Prior austenite grain boundary primary ferrite allotrio-morphs are termed PF(G) in the IIW classi cation scheme

1 Allotriomorphic and idiomorphic primary ferrite

144 Thewlis Classiregcation and quantiregcation of microstructures in steels

Materials Science and Technology February 2004 Vol 20

and are usually observed in the form of polygonal grains orveins as shown schematically in Fig 1 Reference is madein the IIW scheme to polygonal ferrite grains in the intra-granular regions (see Fig 1) of a size approximately threetimes greater than those of the surrounding ferrite laths orgrains These ferrite grains in reality may be cross-sectionsof ferrite allotriomorphs that have grown from prioraustenite grain boundaries beneath the plane of observationand have a wide range of sizes They are termed PF(I) in theIIW scheme The present author and co-workers2 2 havereferred to the different forms of prior austenite grainboundary primary ferrite as GB(PF) so that a distinctionmay be made with idiomorphic primary ferrite as describedbelow

In weld metals stable particle dispersed steels and somemicroalloyed steels ferrite may nucleate not only at theaustenite grain boundaries but also on particles insidethe austenite grains2 2 2 7 (see Fig 2) The author and co-workers2 2 have termed these intragranular ferrite idio-morphs I(PF) Depending on the temperature in thereconstructive regime the intragranular ferrite morpholo-gies2 2 may take the form of blocks loops ellipses rosepetals or wedges The IIW classi cation scheme does nothave a terminology for these primary ferrite idiomorphs

PearliteClassically pearlite transformation may occur at austenitegrain boundariesor an inhomogeneitysuch as an inclusion2 3

Ferrite or cementite nucleation may initiate the pearlitetransformation depending on whether the steel is hypo- orhyper-eutectoid in composition Growth of a pearlite noduleinto an austenite grain proceeds with the formation ofalternate ferrite and cementite plates or lamellae Both thecementite and ferrite possess unique crystallographic orien-tations within the pearlite nodule2 3 Edgewise growth of theplates may occur and also branching of the cementitelamellae The rate controlling process in the growth ofpearlite is the diffusion of carbon As the transformationtemperature is lowered the driving force for the reaction isincreased but the diffusivityof carbon is decreased so that thepearlite interlamellar spacing is decreased

At high transformationtemperatures pearlite is generallyobserved as nodules of alternate ferrite and cementitelamellae that may be quite coarse and degenerate Whenviewed in cross-section the lamellae may appear as aferrite ndash carbide aggregate As the transformation tempera-ture is lowered the lamellae become increasingly neuntil the structure becomes irresolvable under the light

microscope (see Fig 3) The pearlite may then have a lightetching response Alternatively the lamellae may becomesubjected to distortion and bending appearing as a darketching ferritendash carbide aggregate or barely resolvablesomewhat non-lamellar pearlite often described in oldernomenclature as primary troostite2 8 2 9

In the IIW scheme FC(P) is used to describe lamellarpearlite degenerate or coarse pearlite and ne colonyor irresolvable pearlite The term FC is used to describeferrite ndash carbide aggregate At reconstructive transforma-tion temperatures large islands of pearlite or ferrite ndashcarbide aggregate may be interspersed with prior austenitegrain boundary primary ferrite PF(G) A similar situationmay occur with idiomorphic primary ferrite I(PF) (seeFig 4)2 7 In some cases pearlite may be present as micro-phase (see below)

DISPLACIVE TRANSFORMATION REGIMEIn the low temperature displacive transformation regime achange from the austenite to ferrite crystal lattice occurs byan invariant plane strain shape change with a large shearcomponent Diffusion of interstitial carbon atoms mayaccompany the shear transformation For a purely dis-placive transformation there is no movement of atomsacross the ca interface Reactions in the displacive trans-formation regime tend to be rapid The principal phases areWidmanstatten ferrite bainite and martensite

1 intragranular ferrite idiomorphs 2 grain boundary ferriteallotriomorphs

2 Morphologies of ferrite at prior austenite grain bound-ary and intragranular sites in 006C 146Mn sub-merged arc weld metal continuously cooled icedbrine quenched from 670degC22

1 alternate ferritecementite lamellae 2 regne ferrite plusmn carbideaggregate 3 irresolvable pearlite

3 Resolvable and irresolvable pearlite in 083C050Mn as rolled rod

1 idiomorphic ferrite 2 ferrite plusmn carbide aggregate 3 irresolva-ble pearlite

4 Intragranular primary ferrite and pearlite in as cast013C 20Mn cerium sulphide particle dispersedsteel27

Thewlis Classiregcation and quantiregcation of microstructures in steels 145


WidmanstaEgrave tten ferriteA classic feature of Widmanstatten ferrite formation is thatit may occur at relatively low undercooling2 3 The growthmechanism is thought to involve the simultaneous forma-tion of pairs of mutually accommodating plates so that lessdriving force is required for transformation than withbainite or martensite3 0 The ferrite plates grow rapidly witha high aspect ratio (~10 1) resulting in parallel arraysWidmanstatten ferrite is not the result of a purely displacivetransformation but forms by a paraequilibrium mechan-ism3 0 3 1 involving the rapid diffusion of interstitial carbonatoms across the advancing interface into the remainingaustenite during the shear transformation At the relativelylow undercooling required for Widmanstatten ferrite for-mation microphases of retained austenite martensite orferritecarbide aggregate (pearlite) may be formed betweenthe growing ferrite plates

Widmanstatten ferrite can easily be confused with bainiteDube et al1 7 describe both prior austenite grain boundaryWidmanstatten ferrite and bainite as ferrite sideplate FS butreference is also made to intragranular plates IP The IIWclassi cation scheme refers to all forms of Widmanstattenferrite and bainite as ferrite with second phase FS althougha distinction may be made in the terminology whenWidmanstatten ferrite can be positively identi ed egFS(SP)

Characteristically primary Widmanstatten ferrite platesgrow directly from a prior austenitegrain boundarywhereassecondary Widmanstatten ferrite plates grow from allo-trimorphic ferrite at the grain boundaries as shown sche-matically in Fig 5 Primary Widmanstatten ferrite platesmay also grow from inclusions while secondary Widman-statten ferrite plates grow from intragranular idiomorphicferrite2 2 3 2

Widmanstatten ferrite that grows from prior austenitegrain boundary sites is usually seen as colonies of coarsesideplates with aligned microphase (see Fig 6) which aretermed FS(A) in the IIW scheme The individual plateswithin an array are separated by low angle boundaries thatare dif cult to resolve under the light microscope althoughcareful specimen polishing and etching may reveal themDepending on the plane of observation the microphasesmay appear non-aligned When viewing a cross-section offerrite laths that have grown from prior austenite grainboundaries beneath the plane of observation all that maybe seen are islands of microphase in a matrix of ferritewithin the prior austenite grains (see Fig 6) The Widman-statten ferrite is then classi ed as FS(NA) The presentauthor and co-workers2 2 have referred to the differentforms of prior austenite grain boundary Widmanstattenferrite as GB(WF) so that a distinction may be made withintragranular Widmanstatten ferrite as described below

In the intragranular regions of weld metals and insome steels2 2 2 7 3 2 multiple large plates (aspect ratiogt4 1) of Widmanstatten ferrite with aligned microphase

may be observed that grow from inclusions (primaryWidmanstatten ferrite) or from idiomorphic ferrite(secondary Widmanstatten ferrite) as shown in Fig 7The IIW classi cation scheme does not have a terminologyfor these plates However they have been designatedintragranular ferrite sideplates FS(I) in recent work bythe present author3 2 In many cases individual plates maybe observed that have grown relatively unimpeded fromintragranular inclusions (see Fig 8) These plates do nothave aligned microphase and may be interspersed withbainite or martensite2 2 2 7 3 2 The inclusions from which theplates grow may not be viewed since they may be under theplane of observationThese plates have been designated IFPby the present author3 2 who summed FS(I) and IFP to givea total quantity of intragranular Widmanstatten ferritereferred to as I(WF) Where there is a high density ofinclusions multiple hard impingements of individualWidmanstatten ferrite plates growing from inclusions2 2 3 2

may produce a ne interlocking structure (see schematicdiagram Fig 5) The IIW classi cation scheme refersgenerally to this type of structure as acicular ferrite AF(see below)

BainiteBainite is generally recognised as forming at temperatureswhere diffusion controlled transformationsare sluggish andhas features in common with low temperature martensitic

5 Primary and secondary Widmanstatten ferrite

1 idiomorphic ferrite 2 prior austenite grain boundary Widman-staEgrave tten ferrite with aligned microphase 3 prior austenite grainboundary WidmanstaEgrave tten ferrite with non-aligned microphase

6 Interlocking colonies of Widmanstatten ferrite in 005C135Mn HSLA steel submerged arc weld HAZ

7 Intragranular Widmanstatten ferrite sideplates in asdeposited 008C 287Mn 035Mo 00027B0019Ti submerged arc weld metal32 arrow indicatesmultiple plates of Widmanstatten ferrite with alignedmicrophase nucleated on large intragranular inclusions



transformations2 6 It grows as individual plates or sub-unitsto form parallel arrays or sheaves The growth of each sub-unit is accompanied by an invariant plane strain shapechange with a large shear component There is noredistribution of iron or substitutional solute atoms at thetransformation interface Classically bainite has been cate-gorised into two component structures notably upper andlower bainite depending on the transformation tempera-ture Carbon partitions into the residual austenite in upperbainite and precipitates as cementite between the bainiticferrite plates In lower bainite the ferrite becomes super-saturated with carbon and some carbide precipitationoccurs within the ferrite sub-units as well as between them

The exact growth mechanism of bainite is still the subjectof much debate3 3 ndash 3 5 A paraequilibrium mechanism inupper bainite involving a shear transformation accompa-nied by the rapid diffusion of interstitial carbon atomsacross the ca interface would mean that bainitic growth wasin part similar to Widmanstatten ferrite However a purelydisplacive transformation would require no redistributionof atoms across the ca interface A temperature curve To

may be identi ed on the Fe ndash C phase diagram de ningthermodynamically where austenite and ferrite of the samecomposition have identical free energy2 6 3 3 At the To

temperature there is no driving force for transformationThe To curve has a negative slope with carbon concentra-tion lying between the Ae 1 and Ae 3 lines of the Fe ndash C phasediagram In a steel with a carbon concentration lower thanthat de ned by the To curve bainitic ferrite plates maybegin to grow without diffusion at an appropriate holdtemperature then partition excess carbon into the residualaustenite Further diffusionless growth of plates may takeplace from the carbon enriched austenite and the processcontinues until such transformation becomes thermodyna-mically impossible at the To curve This is termed theincomplete reaction phenomenon Continuous undercool-ing of the steel below To will cause the bainite reaction to bemaintained Carbide precipitation occurs when the trans-formation conditions are kinetically favourable For apurely displacive transformation therefore a rapid redis-tribution of carbon atoms is envisaged after the diffusion-less growth of bainitic ferrite sub-units2 6

Bainite can easily be confused with Widmanstatten ferriteas noted above Both structures are referred to as ferritewith second phase FS in the IIW classi cation schemealthougha distinctionmay be made in the terminologywherebainite can be clearly identi ed eg FS(B) A further dis-tinction may be made where upper and lower bainite can bepositively identi ed eg FS(UB) and FS(LB) respectively

Characteristically bainite may grow directly from a prioraustenite grain boundary2 6 or an intragranular inclusion3 6

as shown schematically in Fig 9 Sympathetic nucleation ofbainite plates from existing sheaves is a common feature

Bainite that grows from prior austenite grain boundariesis commonly observed in the form of interlocking sheaves ofvery ne plates with aligned cementite particles (seeFig 10) which are designated FS(A) in the IIW schemeIn upper bainite FS(UB) carbide particles are observedbetween the plates while in lower bainite FS(LB) thecarbides are within as well as between the plates and thestructure tends to have a darker etching response Theindividual plates within a sheaf are separated by low angleboundaries that are virtually irresolvable under the lightmicroscope The sheaves are shown in the process of growthin Fig 11 Extensive sympathetic nucleation is evidentDepending on the plane of observation cementite particlesmay appear non-aligned When viewing a cross-section offerrite laths that have grown from prior austenite grainboundaries beneath the plane of observation all that maybe seen are carbide particles in a matrix of ferrite within theprior austenite grains (see Fig 10) The bainite is thenclassi ed as FS(NA) The present author and co-workers2 2

have referred to the different forms of prior austenite grainboundary bainitic ferrite as GB(B) so that a distinction maybe made with intragranular bainite as described below

In some steels and weld metals2 6 3 2 3 6 bainite sheaves maybe seen to grow from intragranular inclusions (see Fig 12)Individual ne plates of bainitic ferrite may also beobserved that grow relatively unimpeded from intragranu-lar inclusions (see Fig 13) The latter plates do not havealigned carbide particles and may be dif cult to distinguishfrom Widmanstatten ferrite plates IFP (see above) Theinclusions from which the plates grow may not be observed

1 idiomorphic ferrite 2 individual plate of WidmanstaEgrave tten fer-rite nucleated on large intragranular inclusions

8 Growth of intragranular Widmanstatten ferrite platesin 006C 137Mn 017Mo 00028B 0027Tisubmerged arc weld metal continuously cooledhelium quenched from 620degC22

9 Bainite sheaves and sub-units

1 lower bainite with carbide particles between as wellas within subunits 2 upper bainite with aligned carbide3 bainitic ferrite with non-aligned carbide

10 Interlocking sheaves of upper and lower bainite in017C 10Mn steel laser weld HAZ



since they are under the plane of observation The IIWclassi cation scheme does not have a terminology for thedifferent forms of intragranular bainite but the author andco-workers2 2 have termed them I(B) Where there is a highdensity of inclusions multiple hard impingements ofindividual bainitic plates growing from the inclusions may

result in a very ne interlocking structure2 6 3 2 (see schematicdiagram Fig 9) The IIW classi cation scheme refersgenerally to this type of structure as acicular ferrite AF(see below)

MartensiteMartensite is classically an extremely rapid diffusionlesstransformation where carbon is retained in solution3 7 Asthe austenite lattice changes from fcc to the required mar-tensite bcc or bct lattice strain energy considerationsdominate and the martensite is constrained to be in the formof thin plates

In low carbon steels (less than ~02C) lath martensitewith a bcc crystal structure is the commonly occurringform3 7 and is designated M or M(L) in the IIW scheme Themartensite units are formed in the shape of laths thatare grouped into larger sheaves or packets (see Fig 14)The sub-structure consists of a high density of dislocationsarranged in cells each martensite lath is composed of manydislocation cells As the steel carbon content increases signi- cantly above about 02C plate martensite tends to formwith either a bct or bcc crystal structure3 7 The martensiteunits form as individual lenticular plates (see Fig 15) with asubstructure consisting of very ne twins This form ofmartensite is termed twinned martensite in the IIW schemeand is designated M or M(T) Martensite whether in platesor lath form is generally irresolvable under the light micro-scope and tends to have a slow etching response

12 Growth of bainite sheaves from intragranular inclu-sions in 038C 139Mn 0039S 009V0013N steel isothermally transformed 38 s at450degC arrow indicates multiple laths of bainite withcarbide particles between as well as within subunits

11 Growth of bainite sheaves and (arrowed) sympatheticnucleation of laths in 038C 139Mn 0039S009V steel isothermally transformed 45 s at 400degC

13 Growth of intragranular bainite plates in 038C139Mn 0039S 009V 0013N steel isother-mally transformed 38 s at 500degC arrows indicateindividual plates of bainitic ferrite nucleated on smallintragranular inclusions

14 Lath martensite in 013C laser weld metal arrowindicates martensite laths with highly dislocated sub-structure

15 Plate or twin martensite in 027C laser weld metalarrow indicates lenticular martensite with twinnedsubstructure



Acicular ferriteConventionally2 6 acicular ferrite is recognised as an intra-granular nucleated morphology of ferrite in which there aremultiple impingements between grains The acicular ferritenucleates on inclusions inside the prior austenite grainsduring the cda transformation Provided there is a highdensity of inclusions a ne interlocking structure (generallylt5 mm) can be produced

In the IIW scheme acicular ferrite is designated AF Fora long time acicular ferrite was thought to be a singletransformation product Early work3 8 suggested that itwas intragranularly nucleated Widmanstatten ferrite Laterresearch2 6 provided evidence for intragranularly nucleatedbainite However recent research by the author and co-workers2 2 has demonstrated that the nature of acicularferrite may be as shown schematically in Fig 16 Differentreaction products may nucleate on intragranular inclusionsat reconstructive and displacive transformation tempera-

tures during continuous cooling depending on the naturesize and amount of inclusions (see Figs 2 and 17) Acicularferrite results from multiple hard impingements of thedifferent transformation products The sequence oftransformations is consistent with the theoretical activationenergy barrier to nucleation of the different sites Acicularferrite development may thus be de ned in terms of con-ventional steel transformation products and CCT diagramsincorporating both intragranular and grain boundarytransformations

Under continuous cooling transformation conditions

AF~I(PF)zI(WF)zI(B)

This leads to acicular ferrite that may have a variety offorms depending on steel composition cooling rate andinclusion characteristics Acicular ferrite may consist ofmixtures of different intragranular transformationproducts(see Fig 18)2 2 3 2 Alternatively Widmanstatten acicularferrite or bainitic acicular ferrite may form per se2 6 3 8

However if reactions are completed at purely reconstruc-tive transformation temperatures it may be preferable touse the term idiomorphic primary ferrite instead of acicularferrite to describe the microstructure since intragranularprimary ferrite is likely to be coarse and non-acicular inmorphology (see Fig 4)

Acicular ferrite is usually observed as a ne interlockingferrite structure interspersed with microphases (see Fig 18)The shape of the ferrite plates may not appear to be needle-like as the use of the term lsquoacicularrsquo would imply This isbecause the different ferrite morphologies cannot grow veryfar before mutual hard impingement It is evident fromFig 18 that the degree of re nement of the acicular ferrite isdependent on the nature of the transformation productsinherent in its formation

16 Nature of acicular ferrite

a

b

a idiomorphic ferrite (arrowed) nucleated on large inclusionsb WidmanstaEgrave tten ferrite plates (arrowed) nucleated on smallinclusions

17 Acicular ferrite development in 006C 137Mn017Mo 00028B 0027Ti submerged arc weldmetal continuously cooled iced brine quenched from615degC22

a

b

a intragranular primary ferriteplusmn WidmanstaEgrave tten ferrite in C plusmn Mnweld metal22 b intragranular WidmanstaEgrave tten ferrite plusmn bainitein Ti plusmn Mo plusmn B alloyed weld metal32

18 Forms of acicular ferrite



MicrophasesThe different ferrite growth modes of the principal struc-tures described above result in carbon enrichment of theremaining austenite leading to associated second phases ofretained austenite martensite bainite or ferrite ndash carbideaggregate (pearlite) depending on the degree of carbonenrichment of the austenite and the prevailing coolingconditions The second phases associated with Widman-statten ferrite and acicular ferrite are generally quite small(2 ndash 5 mm) and are termed microphases

IIW classi cation scheme problem areasand solutions

The objective in the present work was to investigate the IIWmicrostructure classi cation scheme for weld metals as abasis for quantifying the full range of microstructures foundin plain carbon and low alloy steels as well as ferritic weldmetals and parent plate heat affected zones A means maythus be provided of obtaining database information fordeveloping microstructurendash property relationships or gen-erating data for calibrating physical models that have theprincipal structures primary ferrite pearlite Widmanstat-ten ferrite bainite and martensite as output

It is clear from the above review that while the IIWscheme provides a sound structure for quantifying complexmicrostructures in steels the classi cation of constituentssuch as ferrite sideplate and acicular ferrite is incompatiblewith the principal structures found in the reconstructiveanddisplacive transformation regimes of ferrous materialsKnowledge of the actual transformation products consti-tuting ferrite sideplate and acicular ferrite structures isrequired Classi cation is also needed of idiomorphic ferriteand ferrite sideplate structures growing relatively unim-peded from intragranular inclusions

Problems that may be encountered in relating sub-category microstructural components to principal struc-tures at prior austenite grain boundary and intragranularsites are discussed below together with possible solutionsThe ways in which transformationproducts associated withferrite sideplate and acicular ferrite structures may beidenti ed will be addressed The use of optical microscopywith specimens polished to a 025 mm nish and etched in2 nital is assumed as standard However instances will begiven where different instruments and techniques may beneeded to solve problems Where possible the effects ofsteel composition and heat treatment will be highlightedbut detailed examples are outside the scope of the presentpaper

PRIMARY FERRITEIn low alloy weld metals care has to be taken in identifyingprimary ferrite due to stereological effects Ferrite allo-triomorphs growing from prior austenite grain boundariesbeneath the plane of observation may appear as polygonalferrite grains in the intragranular regions (see Fig 1) Ifthese ferrite allotriomorphs are of a size approximatelythree times greater than those of surrounding acicularferrite laths or grains it is likely that they are the constituentPF(I) described in the IIW scheme It is unlikely that suchlarge grains are idiomorphic ferrite I(PF) nucleated oninclusions as referenced in the literature2 2 since the lattertend to nucleate at lower temperatures with relatively littletime for growth (see Fig 2)

PEARLITEProblems may arise in classifying pearlite when it is presentalong with displacive transformation products

Lamellar pearlite FC(P) in the IIW classi cationscheme may be confused with martensite if the ferritecementite plates are irresolvable under the light microscopeA distinguishing feature is the generally rapid etchingresponse and lower hardness of the pearlite

The dark etching non-lamellar pearlite known as ferrite ndashcarbide aggregate FC in the IIW classi cation scheme maysometimes be confused with bainite The nodular appear-ance of pearlite as opposed to the sheaf appearance ofbainite may provide a distinguishing feature The carboncontent of the steel may also give an indication as to howmuch pearlite may be expected high volume fractionsshould not be present in low carbon steels Ultimatelyhowever knowledge of the thermal history and transforma-tion conditions of the steel may be needed to provide a checkon classi cation (see below) The reconstructive pearlitetransformation should take place slowly at high tempera-tures and over a wide temperature range A displacivetransformation to bainite should take place rapidly at lowertemperatures and over a relatively small temperature range

It is notable that in bainitic steels prolonged holding at agiven temperature may result in the incomplete reactionphenomenon (see above) Continued isothermal treatmentcan result in pearlite formation from the remaining carbonenriched austenite2 6

Dif culties in identi cation of pearlite may be com-poundedbya eutectoid transformationthathasbeen noted incontinuously cooled plain carbon steel (011C 05Mn)This involves ferrite growing in conjunction with repeatednucleation of alloy carbides on the moving ca interphaseboundary3 9 The reaction has been termed interphase pre-cipitation of cementite Dark etching equiaxed ferrite grainscontaining a ne dispersion of carbides are observed underthe light microscope while under the transmission electronmicroscope the cementite is seen in sheets

FERRITE SIDEPLATEBainite and Widmanstatten ferrite may be present insigni cant amounts in heat treated steels and the coarsegrained HAZ of welds but they are dif cult to classifyindividually so that both structures have been generallyreferred to as ferrite sideplate

WidmanstaEgrave tten ferriteClassi cation of Widmanstatten ferrite can prove dif cultbecause of its similarity to upper bainite but certainguidelines may be followed to avoid confusion

The free energy requirement or driving force would beexpected to be lower for Widmanstatten ferrite formationthan for the upper bainite transformation since the formeris thought to grow by the mutual accommodation of platesand the latter by sub-units (see above) All else being equaltherefore Widmanstatten ferrite may be expected to occurat higher temperatures than upper bainite and exhibit agenerally coarser structure with a lower dislocation densityFurthermorethe microphasesbetween Widmanstatten ferritelaths may be expected to be a mixture of pearlite bainitemartensite or retained austenite whereas the nature ofbainite formation (see above) means that cementite particlesmay generally be observed between the bainitic ferriteplates2 6 Microphases may be revealed by the use of dif-ferent chemical etchants (see below)

The identi cation of secondary Widmanstatten ferritewith aligned microphase FS(A) in the IIW scheme isrelatively easy since it grows from existing allotriomorphicferrite but care has to be taken in distinguishing theboundary between the two structures Identi cation ofprimary Widmanstatten ferrite is signi cantly more dif -cult it grows directly from prior austenite grain boundariesand may be more easily confused with upper bainite Theuse of colour etching methods4 0 4 1 in conjunction with



optical microscopy may prove helpful in distinguishingWidmanstatten ferrite from bainiteThese techniquesinvolvecomplex electrochemical reactions and require carefulexperimentation but can provide a means of distinguishingvarious phases by their colouring response Nanohardnessmeasurements may also prove useful these are obtainedusing a modi ed scanning force microscope (SFM)4 2 Thenanoindentation technique allows very small regions ofgrains to be investigated and different phases to be dis-tinguished All else being equal Widmanstatten ferriteshould exhibit a lower hardness than bainite

Although Widmanstatten ferrite may be distinguishedfrom upper bainite using the above guidelines care has tobe taken with stereological effects Widmanstatten ferriteplates within a colony tend to grow in a common crystal-lographic orientation They are therefore generally sepa-rated by low angle boundaries When prior austenite grainboundary Widmanstatten ferrite is seen end-on with non-aligned microphase FS(NA) in the IIW scheme the platescan give the appearance of ferrite grains interspersed withmicrophase thereby creating confusion with regions ofintragranular acicular ferrite AF In the case of acicularferrite hard impingements of the different ferrite morpho-logies growing from inclusions results in high angleboundaries which are signi cantly more distinct than thelow angle boundaries of Widmanstatten ferrite Carefulspecimen polishing and etching may be required to dis-tinguish the two structures

In the intragranular regions of welds it may be relativelystraightforward to identify multiple plates of Widmanstat-ten ferrite with aligned microphase growing unimpededfrom large inclusions described as FS(I) in the literature3 2

Recognising single plates of Widmanstatten ferrite withoutaligned microphase designated IFP may be more dif cultbut these plates are likely to be quite coarse and grow fromlarge inclusions Formation of the latter may appear con-tradictory from a mechanistic viewpoint It is possible thatthe second plate is beneath the plane of observation (seeFig 8) Alternatively the absence of aligned microphasemay be because during plate growth carbon is rejected intothe remaining austenite which then undergoes a secondarytransformation at lower temperatures to bainite martensiteor ne acicular ferrite nucleated on small inclusions

BainiteThe effects of steel composition may compound many of theproblems associated with distinguishing Widmanstattenferrite from upper bainite described above

Low carbon content in bainitic steels can increase thetransformation temperature and result in a coarse lath sizeso that bainitic ferrite with aligned second phase FS(A) inthe IIW scheme appears similar to Widmanstatten ferriteHigh silicon content in bainitic steels (generally gt1) canretard the precipitation of carbide from austenite2 6 andresult in martensite or retained austenite microphasesbetween the bainitic ferrite laths thereby creating confusionwith Widmanstatten ferrite Granular bainite which tendsto form in continuously cooled low carbon bainitic steelsposes a similar problem2 6 This structure appears as arelatively coarse aggregate of bainitic ferrite and retainedaustenite or martensite islands the bainitic sub-units havevery thin regions of austenite between them which cannotbe resolved under the light microscope2 6 Ultimately highresolution SEM TEM or electron back-scattering diffrac-tion (EBSD) techniques4 3 4 4 may be needed to distinguishthese forms of bainite from Widmanstatten ferrite byrevealing the crystallographic sub-structure and thereby themechanism of formation but some electron metallographictechniques are time consuming and often dif cult

When trying to distinguish upper FS(UB) and lowerFS(LB) bainite in the IIW scheme stereological effects may

cause confusion Cross-sections of upper and lower bainitesheavesmay appear similar In generalhowever the carbidesare likely to be ner and the etching response darker in thelower bainite

In weld metals individual plates of bainitic ferrite I(B)growing unimpeded from intragranular inclusions may bedif cult to separate from Widmanstatten ferrite plates IFPHowever the former are likely to be signi cantly ner thanthe latter and the nucleating inclusions may be smallerColour etching methods4 0 4 1 may be helpful for identi ca-tion but ultimately electron metallographic techniques maybe required to determine the nature of the plates

MARTENSITEMartensite is often present together with bainite in the HAZof laser welds and to some extent electron beam welds thesephases also occur in high strength weld metals3 2 Most lowcarbon steels have martensite start temperatures aboveroom temperature so that at slower cooling rates carbonatoms can redistribute and precipitate ie autotemperingcan take place It is then dif cult to distinguish betweenautotempered martensite M and lower bainite FS(LB) inthe IIW scheme The carbides precipitated inside the laths inlower bainite are however likely to be coarser and someinterlath carbide should be evident (see above)

Colouretchingmethods4 0 4 1 maybe investigatedas a meansof distinguishing between bainite and martensite Com-paratively simple nanohardness measurements4 2 may alsoprove useful in separating martensite from other principalstructuresand in distinguishingthe different forms of marten-site Since carbon content generally governs the martensitichardness twinned martensite M(T) may be expected toexhibit a much higher hardness than lath martensite M(L)

ACICULAR FERRITEDistinguishingthe intragranulartransformationproducts thatcompose acicular ferrite AF in the IIW scheme is likely to bevery dif cult comparedwith identifyingthe structure itself It isrecommended therefore that for the purposes of calibratingmodels a pragmatic solution be adopted Thus measuredvolume fractions of acicular ferrite should be compared withthe sum of the intragranularconstituents I(PF)zI(WF)zI(B)predicted by modelling However care should be taken todistinguish between acicular ferrite AF where multipleimpingementoccursbetween the different intragranularferritemorphologies and the intragranular transformationproductsI(PF) I(WF) and I(B) which may grow relatively unimpededand may be identi ed in their own right

MICROPHASESMicrophases are normally revealed using a standard etchpolish technique with a 2 nital etch However problemsmay arise in distinguishing martensite and retainedaustenite which often occur together as MA phase TEMtechniques may be employed to separate the phases but aretime consuming and dif cult The proportion of austenite inthe MA phase may be determined using X-ray diffractiontechniques In some cases etching in picral can reveal thenature of the microphases Thus cementite may appearblack a light brown coloration indicates lath martensite ayellow-brown colour is likely to be twin martensite while agrey-white colour is indicative of retained austenite

New classi cation scheme

In the previous section problems in the IIW microstructureclassi cation scheme were discussed and guidelines pro-posed for identifying the principal structures associated



Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e



with prior austenite grain boundary and intragranular sitestaking into account stereological effects In this section theinformation gained has been used to develop a new classi- cation scheme The application and accuracy of the newscheme have been addressed and consideration given to itsevolution

DEFINITIONUsing the information gained above the traditional IIWclassi cation scheme has been modi ed and new termino-logy de ned as in Table 1 The main and sub-categories ofmicrostructural constituents of the table re ect the mechan-isms of formation of the principal structures and thecharacteristic ferrite morphologies produced in the recon-structive and displacive transformation regimes of steels

Traditionally the IIW classi cation scheme terminologyplaces the transformation product rst and the locationsecond whereas the reverse is often the case in the widerpublished literature1 7 2 2 3 2 For consistency therefore theterminology described in Table 1 follows the traditionalIIW notation Thus the constituents GB(PF) I(PF)GB(WF) I(WF) GB(B) I(B) described in the literature2 2

are replaced by PF(GB) PF(I) WF(GB) WF(I) B(GB)B(I) as main category terms in Table 1 Likewise theconstituent IFP in the literature3 2 is replaced by the sub-category constituent FP(I) in Table 1

To avoid con ict in Table 1 between the terminologyadopted for idiomorphic primary ferrite PF(I) and that forcross-sections of ferrite allotriomorphs growing from prioraustenite grain boundaries below the plane of observationthe latter terminology has been changed from PF(I) toPF(NA) ie primary ferrite not aligned with prior austenitegrain boundaries PF(NA) may be added together withPF(G) to give an overall quantity of reconstructive prioraustenite grain boundary nucleated ferrite PF(GB)

It should be noted in Table 1 that the new sub-categorycomponent terminology automatically de nes its locationeither at prior austenite grain boundaries or in intragranularregions In practice therefore an identi cation system maybe employed which directly links a sub-category componentto the principal structure eg B-FS(A) and WF-FS(A)

Flow charts that incorporate the classi cation andterminology of Table 1 but provide detailed guidance onidentifying principal structures are shown in Fig 19 Thekey to the ow charts is given in Fig 20 Separate charts areprovided for austenite grain boundary and intragranularmicrostructural componentsProgression through the chartsfrom sub-category component structures to the principalstructures is dependent on answering a number of boxedquestions on a yesno basis The questions are derived fromthe considerations made in this paper If the answer to aquestion is lsquoyesrsquo progression is made to the right of thechart towards the principal structure If the answer is lsquonorsquoa move vertically downwards is needed to obtain moreinformation before eventually progress is made to the rightagain The ow charts thus potentially provide a means ofquantifying complex steel microstructures in terms of theprincipal structures thereby enabling the generationof eitherdatabase information or data for calibration of theoreticalmodels

APPLICATIONTo assess the accuracy of the new classi cation scheme andidentify discrepancies between operators exercises werecarried out to quantify widely different microstructuresThe microstructures were obtained by thermally cyclingsteels of compositions 0051 ndash 017C 051 ndash 146Mn in adilatometer to peak temperatures of 900 ndash 1300degC andcooling at rates between 2 and 200 K s2 1 Full details of thequanti cation exercises including a complete statisticalT

able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y



a prior austenite grain boundary constituents b intragranular constituents

19 Guidelines and terminology for identi cation of principal structures



analysis are outside the scope of the present paper Howeverthe results for selected steels are summarised below

Six dilatometer sample microstructures covering a widetransformationtemperature range were photographed usingan appropriate magni cation The resulting microstructural elds are shown in Fig 21 A mesh grid inscribed on trans-parent acetate paper was overlaid in a xed position on thephotographs so that those microstructural constituentsunder or just touching the grid cross-lines could be quanti- ed Each cross-line was identi ed from the grid scale egA1 A2 A3 hellip B1 B2 B3 hellip A total of 500 points wascounted of each eld Because the grid points were xedresults from different operators could be compared and theconstituents that were most dif cult to quantify could berelatively easily identi ed

Initially a single operator was employed to point countthe volume percentages of microstructural constituents inthe six microstructural elds using the traditional IIWand the new classi cation schemes The results (Table 2)demonstrate the advantagesof the new scheme in being ableto rationalise the principal structures associated with ferritesideplate Ultimately the microstructural output is reducedto the ve principal constituents

Following the above exercise different operators wereemployed to determine the volume percentages of the prin-cipal structures in the six microstructural elds using thenew scheme per se The results are shown in the form ofhistograms in Fig 22 Most operators chose to identify themajor transformation products directly although someoperators chose to classify subcategories and thereby themajor components In all cases microphases associatedwith primary ferrite and Widmanstatten ferrite were treatedseparately while bainitic ferrite was quanti ed togetherwith the carbide Because of the xed position of the pointcounting grid the variations in phase proportions in Fig 22

are due to differences in microstructural interpretation bythe individual operators rather than point counting errorsthat would emerge between operators from random reposi-tioning of the grid in the dilatometer sample microstruc-ture When quantifying the volume fraction of secondaryWidmanstatten ferrite some discrepancy occurred betweenoperators owing to the need to distinguish the boundarybetween allotriomorphic ferrite and Widmanstatten ferrite(see Fig 22a) Further differences occurred because ofthe need to distinguish between ferrite carbide aggregate(pearlite) and bainite (see Fig 22b and c) and to someextent lower bainite and autotempered martensite (seeFigs 22d and f) These dif culties were compounded by thelow resolution of the photographic images

A signi cant improvement in the consistency betweenoperators was achieved after appropriate training whenquantifying phase proportions randomly over a relativelylarge area in actual steel samples In this case differentmagni cations could be used to reveal dif cult features Alight microscope with a Swift point counting stage wasemployed to count 500 points of various dilatometer samplemicrostructures again covering a wide transformation tem-perature range The statistical errors in point counting4 5 ndash 4 7

were determined using the formula according to Gladmanand Woodhead4 7

svf=Vf~permil(1Vf )=Pa Š1=2

where sv f is one standard deviation Pa the fraction ofcounts in the a phase and Vf the volume fraction of a phase

The phase proportions obtained by two operators on sixsteels are shown in Fig 23 The 95 con dence limits (2sv f)are superimposed The results show that the phase pro-portions obtained by the individual operators were in manycases within the statistical error de ned in the point count-ing exercise However to obtain a sensible statistical analysis

20 Key to ow charts



of operator bias a larger number of operators is neededFurther work is required in the form of lsquoround robinrsquoexercises to determine the statistical uncertainty betweenoperators when quantifying different types of microstruc-ture and to provide appropriate training measures forwidespread dissemination of the scheme

The above studies were carried out without prior know-ledge of the thermal history of the specimens examinedHowever transformationbehaviour knowledge can providea useful check on results The six microstructural elds inFig 21 were largely representativeof the parent dilatometersample microstructures The corresponding dilation curves

percentage transformed versus temperature graphs andpeak rate transformation curves are shown in Fig 24 Thedilatometer data in Fig 24a show that for this particularsteel transformation began at 793degC and took place over awide temperature range nishing at 628degC As the trans-formation proceeded the rate of transformation increasedslowly to a peak at 715degC and then decreased slowlyindicative of transformation controlled by diffusion Thissupports the operator classi cation for the steel of about70 primary ferrite and 5 pearlite ie predominantlyreconstructive transformation (see Fig 22a) By contrastthe dilatometer data in Fig 24c show that for this steel

a

c

e

b

d

f

a 0051C 051Mn 1200degC 10 K s21 b 017C 052Mn 1300degC 10 K s21 c 013C 102Mn 1300degC 2 K s21 d 013C102Mn 1200degC 10 K s21 e 013C 102Mn 1300degC 50 K s21 f 013C 102Mn 1300degC 200 K s21

21 Microstructural elds of steels thermally cycled in dilatometer to temperatures of 1200 or 1300degC and cooled atrates between 2 and 200 K s21 (800 ndash 500degC)



transformation began at 717degC and nished at 582degC Therate of transformation increased slowly at rst indicative ofreconstructive transformationbut then rose very rapidly toa sharp peak at 646degC before falling steeply and then moreslowly in the nal stages of transformationThe sharp peakin the rate of transformationtook place after around 40 ofreaction had occurred and was indicative of the beginningof shear dominated transformation which should accountfor the remaining 60 of the transformation The highpeak rate transformation temperature is indicative ofWidmanstatten ferrite formation rather than bainite This isbroadly in agreement with the steel microstructure results inFig 22c where around 60 Widmanstatten ferrite wasquanti ed by most of the operators A similar analysis maybe carried out with respect to dilatometer data in Fig 24d Inthis steel the lower peak rate transformation temperature(603degC) and lower nishing temperature (532degC) are indica-tive of bainite as well as Widmanstatten ferrite formationThis again is re ected in the operator microstructureclassi cation in Fig 22d It is notable that in the dilatometerdata of Fig 24f almost 50 of the steel transformationoccurred at one temperature (421degC) This extremely rapidreaction rate and low transformation temperature areindicative of martensite transformation in agreement withthe operator classi cation for the steel in Fig 22f

Overall the above exercises show that a reasonabledegree of consistency may be obtained between operatorswhen using the new classi cation scheme to identify theprincipal structures (primary ferrite pearlite martensite)and the transformation products constituting ferrite side-plate structures notably Widmanstatten ferrite and bainite

EVOLUTIONThe new classi cation scheme de ned abovehas attempted toplace knowledge of the classi cation and quanti cation ofsteel microstructureson a rm contemporarybasis Howeverit is of interest to consider possible future developments

The guidelines proposed for phase recognition in the newscheme are based on the mechanisms of formation of prin-cipal structures but there are still questions to be addressedwith respect to the kinetics of reactions notably clari ca-tion of the growth mechanism of bainite Improved know-ledge in this area should result in greater accuracy indistinguishing bainite from other phases Overall a betterunderstanding is needed of the dynamics of phase trans-formations under continuous cooling transformation con-ditions where phases may form simultaneously and local uctuations in transformation conditions can make itdif cult to recognise the transition between one phase

Table 2 Volume percentages of microstructural constituents obtained by single operator point counting microstructural elds (see Fig 21) using traditional IIW and new classi cation schemes

New scheme IIW scheme

Principal structure Phase Component structure Phase

0051C 051Mn 1200degC 10 K s2 1 (Fig 21a)PF 726 PF(G) 726

PF(NA) 0P 64 FC(P) 07

FC 57WF 210 FS(A)zFS(NA) 108z102B 0M 0 M 0

017C 052Mn 1300degC 10 K s2 1 (Fig 21b)PF 197 PF(G) 197

PF(NA) 0P 547 FC(P) 24


013C 102Mn 1300degC 2 K s2 1 (Fig 21c)PF 284 PF(G) 284

PF(NA) 0P 94 FC(P) 16

FC 78WF 364 FS(A)zFS(NA)zFS(LB)zFS(I) 341z209z17z03B 206M 52 M 52

013C 102Mn 1200degC 10 K s2 1 (Fig 21d)PF 147 PF(G) 147

PF(NA) 0P 26 FC(P) 26

FC 0WF 555 FS(A)zFS(NA)zFS(LB) 302z312z167B 226M 46 M 46

013C 102Mn 1300degC 50 K s2 1 (Fig 21e)PF 0 PF(G) 0

PF(NA) 0P 0 FC(P) 0


013C 102Mn 1300degC 200 K s2 1 (Fig 21f)PF 0 PF(G) 0

PF(NA) 0P 0 FC(P) 0




and another In this respect an atlas of optical micrographswith associated heat treatments and phase proportionswould be a useful accompaniment to the new classi cationscheme Scanning electron images with their greaterresolution may be employed to describe local features Itshould be noted that a compendium of weld metal micro-structures exists to accompany the traditional IIW classi- cation scheme1 9

The classi cation and quanti cation of complex steelmicrostructures by metallographic techniques is by naturelabour intensiveand it is appropriateto questionthe extent towhich computers may carry out such activities There hasbeen a signi cant amount of work done with regard to imageprocessing in recent years driven by the advances in com-puter technology4 8 The appropriate processing steps dependon the type of information required The measurement ofimages generally requires that features be well de ned byedges size or unique brightness and colour Image analysisthen attempts to nd numeric descriptive parameters thatsuccinctly represent the information of importance in theimage The new classi cation scheme developed in the currentwork provides guidelines on the important features forphase recognition It may thus be possible to train an imageanalysis system to recognise these features The question asto how such information can be processed and analysed bycomputeris a matter for furtherresearchHowever continuedrapid advances in computer power and image resolution maymake this type of activity tractable in the not too distant future

Summary and conclusions

The InternationalInstitute of Welding (IIW) microstructureclassi cation scheme for weld metals has been investigated

as a basis for quantifying the full range of microstructuresfound in plain carbon and low alloy steels as well as ferriticweld metals and parent plate heat affected zones Thefollowing conclusions have been drawn

1 The IIW scheme provides a sound structure for quanti-fying complex microstructures in steels but the classi ca-tion of constituents such as ferrite sideplate and acicularferrite is incompatible with the principal structures found inthe reconstructive and displacive transformation regimes ofsteels There is no classi cation in the IIW scheme ofidiomorphic ferrite and ferrite sideplate structures growingrelatively unimpeded from intragranular inclusions

2 There are problems in relating sub-category micro-structural constituents in the IIW scheme to principal struc-tures at prior austenite grain boundary and intragranularsites owing to stereological and morphological effects Thesehave been discussed in detail and solutions proposed Theways in which transformation products associated withferrite sideplate and acicular ferrite structures may beidenti ed have been de ned

3 A new classi cation scheme has been formulated Themicrostructure classi cation and terminology used in theIIW scheme have been built upon and new terminologyincorporated into a table providing descriptions of theprincipal structures and sub-category components Flowcharts have been devised with guidelines for identifying theprincipal structures

4 The new classi cation scheme has been used toquantify microstructures covering a wide transformationtemperature range A difference in interpretation between

22 Volume percentages of principal structures obtainedby different operators point counting microstructural elds (see Fig 21) using new classi cation schemePF~primary ferrite P~pearlite WF~Widmanstattenferrite B~bainite M~martensite

a 0051C 051Mn 1200degC 10 K s2 1 b 017C 052Mn1300degC 10 K s21 c 013C 102Mn 1300degC 2 K s21 d013C 102Mn 1200degC 10 K s21 e 013C 102Mn1300degC 50 K s2 1 f 013C 102Mn 1300degC 200 K s21

23 Volume percentages of principal structures obtainedby two different operators point counting microstruc-ture of steels under light microscope using new classi -cation scheme PF~primary ferrite P~pearlite WF~Widmanstatten ferrite B~bainite M~martensite



individual operators has been identi ed by point countingmicrographsusing a xed grid Some discrepancyoccurred inidentifying the boundarybetween allotriomorphicferrite andWidmanstatten ferrite distinguishing between ferrite ndash car-bide aggregate (pearlite) and bainite and differentiatingbetween lower bainite and autotempered martensite Withappropriate training phase proportions obtained by twoindividual operators point counting steel microstructures atrandom using the light microscopewere in many cases withinthe statistical error de ned in the point counting exercise

5 Overall a reasonable degree of consistency can beobtained between operators when using the new scheme toidentify and quantify the principal structures (primaryferrite pearlite martensite) and the actual transformationproducts constituting ferrite sideplate structures notablyWidmanstatten ferrite and bainite Further work is requiredin the form of lsquoround robinrsquo exercises to determine thestatistical uncertainty between operators when quantifyingdifferent types of microstructure and to identify appro-priate training measures for widespread dissemination ofthe scheme

6 A means has been provided of obtaining databaseinformation for developing microstructurendash property rela-tionships or generating data for calibrating physical modelsthat have the principal structures as their output

Acknowledgements

The author would like to thank Dr S V Parker Dr N AWhittaker Dr P L Harrison Dr C Wildash Dr J ButlerDr S A Butler Professor A A Howe and I W Martin ofCorus RDampT for helpful discussions and suggestions Theauthor is also grateful to Professor R C ThomsonLoughborough University and Dr D J Abson TWI forhelpful comments Thanks are nally extended to ECSCpartners at TWI (UK) CSM (Italy) CEIT (Spain) andIRSID (France) for support under ECSC steel researchprogramme 7210PR245(F50100)

References

1 b donnay j c jerman v leroy u lotter r grossterlindenand h pircher Proc Int Conf on lsquoModelling of metalrolling processesrsquo London UK December 1996 London TheInstitute of Materials

2 j k lee and h n han in lsquoThermomechanical processing ofsteelsrsquo Vol 1 245 ndash254 2000 London The Institute ofMaterials

3 a j trowsdale k randerson p f morris z husain and

24 Transformation data obtained from thermally cycled steels in Fig 21



d n crowther in lsquoThermomechanical processing of steelsrsquoVol 1 332ndash 341 2000 London The Institute of Materials

4 s v parker lsquoModelling of phase transformations in hot rolledsteelsrsquo PhD thesis University of Cambridge UK 1997

5 h k d h bhadeshia and l e svensson in lsquoMathematicalmodelling of weld phenomenarsquo 109ndash 174 1993 London TheInstitute of Materials

6 s j jones Modelling inclusion potency and simultaneoustransformation kinetics in steelsrsquo PhD thesis University ofCambridge UK 1996

7 s j jones and h k d h bhadhesia Acta Metall 1997 45(7) 2911ndash 2820

8 k ichikawa and h k d h bhadhesia in lsquoMathematicalmodelling of weld phenomena 4rsquo 302ndash 320 1998 London TheInstitute of Materials

9 d j c mackay in lsquoMathematical modelling of weld phe-nomena 3rsquo 359ndash 389 1997 London The Institute of Materials

10 r c reed lsquoThe characterisation and modelling of multipasssteel weld heat affected zonesrsquo PhD thesis University ofCambridge UK 1990

11 k e easterling in lsquoMathematical modelling of weld phe-nomenarsquo 183ndash 200 1993 London The Institute of Materials

12 m atkins lsquoAtlas of continuous cooling transformationdiagrams for engineering steelsrsquo 1977 Swinden LaboratoriesRotherham British Steel Corporation (ISBN 0 9500451 44)

13 z zhang and r a farrar lsquoAn atlas of continuous coolingtransformation diagrams applicable to low carbon low alloyweld metalsrsquo 1995 London The Institute of Materials

14 b l bramfittand j g speer Metall Trans 199021A 817ndash 82915 y ohmori h ohtsubo y c jung s okaguchi and h otani

Metall Trans 1994 25A 1981ndash 198916 u lotter and h p hougardy Prakt Metallogr 1992 29 (3)

151ndash 15717 c a dubE h i aaronson and r f mehl Rev Metall 1958

55 20118 h i aaronson lsquoDecomposition of austenite by diffusional

processesrsquo 389 1960 Philadelphia PA AIME19 lsquoCompendium of weld metal microstructures and propertiesrsquo

1985 Abington Woodhead Publishing20 lsquoClassi cation of microstructures in low carbonndash low alloy

steel weld metal and terminologyrsquo Committee of WeldingMetallurgy of Japan Welding Society IIW Doc IX ndash 1282ndash 83

21 e anelli and p e di nunzio lsquoClassi cation of microstructuresof low carbon steels preparation of a set of standardmicrographsrsquo ECSC Agreement 7210ndash EC405 (94ndash D302a)CSM Rome Italy June 1996

22 g thewlis j a whiteman and d j senogles Mater SciTechnol 1997 13 (3) 257ndash 274

23 r w k honeycombe and h k d h bhadeshia lsquoSteels ndashmicrostructure and propertiesrsquo 2nd edn 35 1995 LondonEdward Arnold

24 k m wu t yokomizo and m enomoto ISIJ Int 2002 421144ndash 1149

25 g myamoto t furuhara and t maki CAMP ISIJ 2001 141172

26 h k d h bhadeshia lsquoBainite in steelsrsquo 1st edn 1992 LondonThe Institute of Materials

27 g thewlis lsquoStable sulphide particle dispersed steelrsquo Interna-tional Patent Application 01052182 Corus UK Ltd Mar 2000

28 r m brick and a phillips lsquoStructure and properties of alloysrsquo2nd edn 334ndash 337 1949 New York McGraw-Hill

29 a g guy lsquoElements of physical metallurgyrsquo 2nd edn474ndash 476 1960 Reading MA Addison-Wesley

30 h k d h bhadeshia Acta Metall 1981 29 1117ndash 113031 j w christian lsquoMilitary transformations ndash an introductory

surveyrsquo 1 ndash 19 1965 London The Iron and Steel Institute32 g thewlis Sci Technol Weld Joining 2000 5 (6) 365ndash

37733 h k d h bhadeshia and j w christian Metall Trans A

1990 21A 767ndash 79734 h k d h bhadeshia Mater Sci Eng A 1999 A273 ndash A275

58 ndash 6635 subra suresh (ed) Scr Mater 2002 47 (3) (Viewpoint Set on

lsquoBainitersquo)36 madariaga i gutierrez and h k d h bhadeshia Metall

Trans A Sept 2001 32A 218737 g r speich and w c leslie Metall Trans 1972 3 1043ndash

105438 r a ricks p r howell and g s barritte J Mater Sci

1982 17 73239 a t davenport and p c becker Mater Trans 1971 2

296240 e beraha and b shpiglar lsquoColour metallographyrsquo 1977

Metal Park OH American Society for Metals41 w fin lsquoBasic principles for colour metallographyrsquo 1983

Beijing Beijing Industry University42 p maier a richter r g faulkner and r ries Mater

Charact 2002 48 329ndash 33943 i m watt lsquoThe principles and practice of electron microscopyrsquo

2nd edn 1997 Cambridge Cambridge University Press44 a j schwartz m kumar and b l adams lsquoElectron

backscatter diffraction in materials sciencersquo 2000 New YorkKluwerPlenum

45 f weinberg lsquoTools and techniques in physical metallurgyrsquoVol 1 272ndash 275 1970 New York Marcel Dekker

46 b pickering lsquoThe basis of quantitative metallographyrsquo 8 ndash 101976 London Metals and Metallurgy Trust for the Institute ofMetallurgical Technicians

47 t gladman and j h woodhead J Iron Steel Inst 1960 194189

48 j c russ lsquoThe image processing handbookrsquo 2nd edn 1995Boca Raton FL CRC Press



morphologies (often classed as bainite) Widmanstattenferrite was dif cult to place but was regarded as a genericallysimilar structure to bainite Intragranularcomponent phasessuch as acicular ferrite posed a much greater degree ofdif culty Much effort was made by the welding fraternity inthe 1980s to develop an overallmicrostructurequanti cationscheme for weld metals incorporating both prior austenitegrain boundary and intragranular nucleated constituentsand addressing stereological effects ie the way constituentsare orientated in space1 9 20 A scheme was devised whichbecame recognised as the International Institute of Welding(IIW) classi cation1 9 Most of the constituents de ned in theIIW scheme were relatively easily identi ed Furthermorethe scheme could just as readily be applied to steels whereaustenite grain boundary transformations dominate as toweld metals where intragranulartransformationsare the ruleHowever identi cation of the actual transformation pro-ducts constituting component structures such as ferritesideplate and acicular ferrite has proved dif cult Anelliand Di Nunzio2 1 recently devised a scheme providingguidance on identifying transformation products associatedwith sideplate structures which has had some success butstereological effects and intragranular constituents were nottreated in depth

The objective in the current work has therefore been toinvestigate the IIW microstructure classi cation scheme as abasis for quanti cation of complex microstructures in steelsThe overall aim has been to develop a scheme that althoughrequiring a basic knowledge as to the mechanism of for-mation of the principal structures will be relatively easy touse given optical microscopy standard specimen polishingand etching techniques and appropriate guidance Theapproach has been to review microstructural constituentsin the IIW scheme in the context of the development ofprincipal structures found in the reconstructive and dis-placive transformation regimes of steels Detailed intragra-nular as well as austenite grain boundary transformationproducts have been considered and also stereological effectsProblems relating microstructural constituents to principalstructures in the IIW scheme have been investigatedtogether with possible solutions so that a new quanti cationscheme may be developed with a much broader applicationrange The intention has been to cover microstructuresobserved in carbon (up to abount 08) and low alloy (up toapproximately 5) steels as well as weld metals (up to010C and 5 alloy) and weld HAZs

Classi cation of microstructures andterminology

In this section the mechanisms of formation of the principalstructures and the characteristic ferrite morphologies pro-duced in the reconstructive and displacive transformationregimes of ferrous materials are brie y reviewed Theclassi cation and terminology used in the IIW scheme aredescribed together with that of Dube et al1 7 to provide alink with the early work on classi cation of prior austenitegrain boundary ferrite morphologies Terminology used inrecent work by the present author and co-workers2 2 is alsoincluded to provide a contemporary view of complex intra-granular transformations including those generating themicrostructure commonly known as acicular ferrite

RECONSTRUCTIVE TRANSFORMATIONREGIMEIn the high temperature reconstructive transformationregime a change from the austenite to ferrite crystal struc-ture occurs by a reconstructionprocess involving movementof atoms across the ca transformationinterfaceThe principal

phases are ferrite and pearlite Reactions tend to bediffusion controlled with slow rates

FerriteIn low hardenability materials the rst phase usuallyforming on prior austenite grain boundaries during coolingbelow the Ae3 temperature is classically referred to asallotriomorphic ferrite as shown schematically in Fig 1The ferrite nuclei have a Kurdjumovndash Sachs (K ndash S) orien-tation relationship with one austenite grain and grow intothe adjacent austenite grain with which they should normallyhave a random orientation relationship2 3 At some lowertemperature ferrite may begin to nucleate on inclusionsinside the austenite grains2 2 2 4 and this is termed idiomor-phic ferrite (see Fig 1) The indications are that ferriteidiomorphs do not have a xed orientation relationshipwith the matrix grains into which they grow2 5

Growth at reconstructive transformation temperaturestends to be controlled by substitutional element diffusionaway from the ca interface at low undercooling and carbondiffusion at high undercooling Various growth modesare recognised in order of decreasing transformationtemperature2 6

(i) local equilibrium with bulk partition of substitu-tion alloying elements (PLE)

(ii) local equilibrium with negligible partition of sub-stitutional alloying elements (NPLE)

(iii) paraequilibrium where only the interstitial carbonatoms diffuse

The diffusion rate of carbon in austenite may be manyorders of magnitude greater than that of substitutionalatoms at reconstructive transformation temperatures Trueequilibrium segregation during phase transformations atmigrating interfaces is therefore unlikely to be achieved withregard to all components Growth under diffusion controlwith local equilibrium at the interface is then envisagedTwo phases may differ either signi cantly (PLE) ornegligibly (NPLE) in terms of substitutional alloy contentElement concentration or depletion spikes are invoked tosatisfy the thermodynamic constraints In many cases asthe transformation temperature is decreased the relativerates at which elements are able to diffuse negate theassumption of local equilibrium since the interface com-position spike would be only several atomic layers thick Insuch cases the concept of paraequilibrium is applied iethere is no redistribution of iron or substitution atoms at theinterface between the phases and only the interstitial carbonatoms diffuse The different growth modes described abovemay result in signi cant changes in ferrite growth mor-phology from equiax grains towards a plate shape (seebelow)

Dube et al1 7 refer to prior austenite grain boundaryallotriomorphic ferrite as GBF The IIW classi cationscheme refers to the rst phase forming at reconstructivetransformation temperatures as primary ferrite termed PF

Prior austenite grain boundary primary ferrite allotrio-morphs are termed PF(G) in the IIW classi cation scheme

1 Allotriomorphic and idiomorphic primary ferrite

































































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References





















































































































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References





































































































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References























































































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References






































































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References



























































AF~I(PF)zI(WF)zI(B)





a

b



a

b







































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References

























































































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References








































































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References























































Tab

le1

Cla

ssi

cati

onsc

hem

efo

rm

icro

stru

ctur

alco

nsti

tuen

ts

Cate

go

ryte

rmin

olo

gy

Pri

ncip

al

str

uctu

recla

ssi

regcati

on

Ov

era

llM

ain

Su

bC

om

po

nen

tst

ruct

ure

descr

ipti

on

Co

mm

en

ts

Rec

on

stru

ctiv

etr

ansf

orm

atio

ns

(dif

fusi

onco

ntro

lled

w

ith

slo

wra

tes

ofre

acti

on

)Ferr

ite

PF

PF(G

B)

PF(G

) G

rain

bo

un

dary

pri

mary

ferr

ite

All

otr

iom

orp

hic

ferr

ite

Po

lyg

on

al

ferr

ite

Ferr

ite

vein

s

Ferr

ite

vein

so

rp

oly

go

nal

gra

ins

alig

ned

wit

hp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

PF(N

A)

Po

lyg

on

al

pri

mary

ferr

ite

no

n-

ali

gn

ed

Po

lyg

on

al

ferr

ite

gra

ins

wit

hin

the

pri

or

au

ste

nit

eg

rain

so

fa

size

ap

pro

xim

ate

lyth

ree

tim

es

gre

ate

rth

an

the

su

rro

un

din

gfe

rrit

ela

ths

or

gra

ins

cro

ss-

secti

on

so

ffe

rrit

eallo

trio

mo

rph

sth

at

have

gro

wn

fro

mp

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bserv

ati

on

PF(I

)P

F(I

)Id

iom

orp

hic

ferr

ite

Ferr

ite

idio

mo

rph

sass

oci

ate

dw

ith

intr

ag

ran

ula

rn

ucle

ati

on

site

s(l

arg

eo

xid

es

ulp

hid

ein

clu

sio

ns)

inw

eld

meta

lsan

dp

art

icle

dis

pers

ed

steels

Pearl

ite

P

P

FC

(P)

Lam

ellar

pearl

ite

Deg

en

era

tep

earl

ite

Fin

eco

lon

yp

earl

ite

No

du

les

of

alt

ern

ate

ferr

itec

em

en

tite

lam

ell

ae

wh

ich

are

oft

en

dif

regcu

ltto

reso

lve

un

der

the

op

tical

mic

rosc

op

e

Th

estr

uct

ure

has

ara

pid

etc

hin

gre

spo

nse

in2

nit

al

an

da

gen

era

lly

low

hard

ness

Pearl

ite

may

be

pre

sen

tas

am

icro

ph

ase

FC

Ferr

ite

plusmncarb

ide

ag

gre

gate

Pearl

ite

lam

ell

ae

vie

wed

incro

ss-s

ecti

on

D

isto

rted

pearl

ite

lam

ellae

may

ap

pear

as

ad

ark

etc

hin

gvir

tuall

yir

reso

lvab

lefe

rrit

ec

arb

ide

ag

gre

gate

kno

wn

as

pri

mary

tro

osti

te

Dif

regcu

ltto

dis

tin

gu

ish

ferr

itec

arb

ide

ag

gre

gate

fro

mb

ain

ite

Dis

pla

cive

tran

sfo

rmat

ion

s(s

hea

rd

om

inat

ed

wit

hra

pid

rate

so

fre

acti

on)

Wid

man

staEgravett

en

ferr

ite

WF

WF

(GB

)FS

(A)

Wid

man

staEgravett

en

ferr

ite

wit

hali

gn

ed

mic

rop

hase

Wid

man

staEgravett

en

ferr

ite

sid

ep

late

s

Co

lon

ies

of

para

llel

ferr

ite

lath

s(o

rsid

ep

late

s)w

ith

mic

rop

hases

ali

gn

ed

betw

een

the

lath

sra

ng

ing

fro

mp

earl

ite

tom

art

en

site

Lath

bo

un

dari

es

are

dif

regcu

ltto

reso

lve

Pri

mary

Wid

ma

nstaEgrave

tten

ferr

ite

gro

ws

fro

mth

ep

rio

rau

sten

ite

gra

inb

ou

nd

ari

es

wh

ere

as

seco

nd

ary

Wid

man

staEgrave

tten

ferr

ite

gro

ws

fro

mall

otr

iom

orp

hic

ferr

ite

at

the

bo

un

dary

FS

(NA

) W

idm

an

staEgravett

en

ferr

ite

wit

hn

on

-alig

ned

mic

rop

hase

Ag

gre

gate

of

mic

rop

hase

isla

nd

san

dW

idm

an

staEgravett

en

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-s

ecti

on

so

fW

idm

an

staEgravett

en

ferr

ite

sid

ep

late

sth

at

gro

wfr

om

pri

or

au

sten

ite

gra

inb

ou

nd

ari

es

belo

wth

ep

lan

eo

fo

bse

rvati

on

WF

(I)

FS

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sM

ult

iple

coars

eW

idm

an

staEgrave

tten

ferr

ite

pla

tes

(asp

ect

rati

og

reate

rth

an

41

)w

ith

alig

ned

mic

rop

hase

sw

hic

hg

row

fro

min

trag

ran

ula

rin

clu

sio

ns

Pri

mary

intr

ag

ran

ula

rfe

rrit

esi

de

pla

tes

gro

wfr

om

inclu

sio

ns

wh

ere

as

seco

nd

ary

sid

ep

late

sg

row

fro

mfe

rrit

eid

iom

orp

hs

ass

oci

ate

dw

ith

incl

usio

ns

FP

(I)

Intr

ag

ran

ula

rW

idm

an

staEgrave

tten

ferr

ite

pla

tes

Ind

ivid

ual

coars

ep

late

so

fW

idm

an

staEgrave

tten

ferr

ite

that

gro

wre

lati

ve

lyu

nim

ped

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Wid

man

staEgravett

en

aci

cula

rfe

rrit

eFin

ein

terl

ocki

ng

str

uct

ure

form

ed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

Wid

man

staEgrave

tten

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Bain

ite

BB

(GB

)FS

(A)

Bain

itic

ferr

ite

wit

hali

gn

ed

carb

ide

Bain

ite

sheaves

Sh

eaves

of

para

llel

ferr

ite

lath

s(o

rsu

b-u

nit

s)w

ith

cem

en

tite

part

icle

salig

ned

betw

een

the

lath

s

Lath

bo

un

dari

es

are

gen

era

lly

irre

solv

ab

leu

nd

er

the

lig

ht

mic

rosco

pe

Sh

eaves

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

sym

path

eti

cn

ucl

ea

tio

no

fla

ths

fro

mexis

tin

gsh

eaves

isa

co

mm

on

featu

reFS

(NA

) B

ain

itic

ferr

ite

wit

hn

on

-alig

ned

carb

ide

Ag

gre

gate

of

co

ars

eca

rbid

es

an

db

ain

itic

ferr

ite

wit

hin

the

pri

or

au

sten

ite

gra

ins

cro

ss-

secti

on

so

fb

ain

ite

sh

eave

sth

at

gro

wfr

om

pri

or

au

ste

nit

eg

rain

bo

un

dari

es

(or

exis

tin

gsh

eaves)

belo

wth

ep

lan

eo

fo

bserv

ati

on

FS

(UB

) U

pp

er

Bain

ite

Carb

ide

part

icle

sare

pre

cip

itate

db

etw

een

the

bain

ite

sub

-un

its

Up

per

bain

ite

has

ah

igh

er

dis

loca

tio

nd

en

sit

yth

an

pri

mary

Wid

man

staEgravett

en

ferr

ite

Bain

ite

may

ap

pear

as

am

icro

ph

ase

betw

ee

nW

idm

an

staEgrave

tten

ferr

ite

sid

ep

late

sFS

(LB

) Lo

we

rb

ain

ite

Fin

ecem

en

tite

part

icle

sp

recip

itate

dw

ith

inas

well

as

betw

een

bain

itic

ferr

ite

pla

tes

Lo

wer

bain

ite

has

ag

en

era

lly

dark

er

etc

hin

gre

sp

on

se

than

up

per

bain

ite

Dif

regcu

ltto

dis

tin

gu

ish

low

er

bain

ite

fro

mau

tote

mp

ere

dm

art

en

sit

e











able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References































































able

1(C

on

tin

ued

) Cate

go

ryte

rmin

olo

gy

Pri

nci

pal

str

uct

ure

cla

ssi

regcati

on

Overa

llM

ain

Su

bC

om

po

nen

tstr

uct

ure

desc

rip

tio

nC

om

men

ts

B(I

)FS

(I)

Intr

ag

ran

ula

rb

ain

ite

sh

eaves

Sh

eaves

of

regn

eb

ain

itic

ferr

ite

pla

tes

wit

halig

ned

carb

ide

wh

ich

gro

wfr

om

intr

ag

ran

ula

rin

clu

sio

ns

FP

(I)

Intr

ag

ran

ula

rb

ain

ite

pla

tes

Ind

ivid

ual

regn

ep

late

so

fb

ain

itic

ferr

ite

that

gro

wre

lati

vely

un

imp

ed

ed

fro

min

trag

ran

ula

rin

clu

sio

ns

AF

Bain

itic

acic

ula

rfe

rrit

eV

ery

regn

ein

terl

ock

ing

stru

ctu

refo

rmed

by

mu

ltip

leim

pin

gem

en

tso

fin

div

idu

al

bain

itic

ferr

ite

pla

tes

gro

win

gfr

om

intr

ag

ran

ula

rin

clu

sio

ns

Mart

en

site

M

M

M(L

) Lath

mart

en

sit

eLo

wca

rbo

nm

art

en

sit

ew

ith

ala

thstr

uct

ure

an

dh

eavily

dis

loca

ted

su

b-s

tru

ctu

re

Lath

mart

en

site

has

aslo

wetc

hin

gre

sp

on

sein

2

nit

al

an

da

gen

era

lly

hig

hh

ard

ness

Co

lon

ies

of

mart

en

sit

em

ay

form

wit

hin

the

pri

or

au

ste

nit

eg

rain

s

Sm

aller

colo

nie

sm

ay

be

treate

das

mic

rop

hases

Mic

rop

hase

sm

ay

co

nsi

st

of

mart

en

sit

ew

ith

reta

ined

au

sten

ite

(MA

)M

(T)

Tw

inm

art

en

site

Hig

hcarb

on

mart

en

site

wit

ha

pla

testr

uctu

rean

dtw

inn

ed

su

b-s

tru

ctu

re

Re

tain

ed

IIW

term

ino

log

y

















20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References





































































20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References

































































20 Key to ow charts






a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References


























































a

c

e

b

d

f













PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References































































PF(NA) 0P 64 FC(P) 07



PF(NA) 0P 547 FC(P) 24



PF(NA) 0P 94 FC(P) 16



PF(NA) 0P 26 FC(P) 26



PF(NA) 0P 0 FC(P) 0



PF(NA) 0P 0 FC(P) 0





















Acknowledgements


References








































































Acknowledgements


References


























































Acknowledgements


References







































































































The2004 Classification Quantification Microstructures Steels

Documents