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MECHANICAL ENGINEERING DEPARTMENT SEM – III (MATERIAL SCIENCE AND METALLURGY)

1 GOVERNMENT ENGINEERING COLLEGE, GODHRA

INDEX

SR.

NO

TITLE PAGE DATE OF

START

COMPLE

TION

DATE

SIGN. OF

FACULTY

GR.

Fro

m

To

1.

TO STUDY ABOUT BASICS OF

MATERIAL SCIENCE AND

METALLURGY

2. TO STUDY ABOUT METALLIC

MATERIALS.

3. TO STUDY ABOUT THE

EFFECTS OF ALLOYING METALS.

4.

TO STUDY MACRO

EXAMINATION & MICRO

EXAMINATION.

5.

TO PERFORM MICRO

EXAMINATION OF STANDARD

PIECES.

6.

TO STUDY ABOUT IRON

CARBON DIAGRAM &

ALLOTROPY OF IRON.

7. TO STUDY ABOUT CAST IRON.

8.

TO STUDY ABOUT HEAT

TREATMENT AND CHECK

EFFECT OF QUENCHING MEDIA

ON HARDNESS OF STEEL.



SR.

NO

TITLE PAGE DATE OF

START

COMPLE

TION

DATE

SIGN. OF

FACULTY

GR.

Fro

m

To

9.

TO MEASURE HARDENABLITY

OF GIVEN MATERIAL WITH

JOMINY HARDENABILITY TEST

10.

TO PERFORM DYE

PENETRATION TEST FOR GIVEN

SAMPLE

11.

TO STUDY OF MAGNETIC

PARTICLE TEST

12.

TO STUDY OF ULTRASONIC

TEST



INSTRUCTIONS *

THIS LABORATORY MANUAL IS ISSUED ONCE ONLY. THIS IS YOUR RESPONSIBILITY TO

PRESERVE IT IN GOOD CONDITION UP TO TERM WORK SUBMISSION & ORAL EXAMINATION.

YOUR WRITING SHOULD BE NEAT AND CLEAN.

GET CHECKED YOUR MANUAL AT THE END OF THE PERFORMANCE OF EACH PRACTICAL.

PRACTICAL & TUTORIALS THAT CANNOT BE READ OR ARE NOT PRESENTED IN A

PROFESSIONAL ENGINEERING STYLE WILL NOT RECEIVE CREDIT (HIGHER GRADES).



SYLLABUS

MATERIAL SCIENCE AND METALLURGY

1. INTRODUCTION TO MATERIAL SCIENCE AND METALLURGY: CLASSIFICATION OF

ENGINEERING MATERIALS, ENGINEERING REQUIREMENTS OF MATERIALS, PROPERTIES

OF ENGINEERING MATERIALS, CRITERIA FOR SELECTION OF MATERIALS FOR

ENGINEERING APPLICATIONS.

2. METALLIC MATERIALS: TYPES, PROPERTIES AND APPLICATIONS, STRUCTURE OF

METALS, FRACTURE, MACRO-EXAMINATION, SPARK TEST, SCULPTURES PRINT, MACRO-

ETCHING, MICROSCOPIC EXAMINATIONS, MAGNETIC TESTING, CHEMICAL ANALYSIS OF

STEEL AND IRON FOR CARBON, SULPHUR & PHOSPHOROUS.

3. IRON-CARBON DIAGRAM, PLAIN CARBON STEELS, ALLOTROPY OF IRON.

4. CRYSTALLIZATION OF METALS, SOLIDIFICATION OF AN ALLOY, SOLID SOLUTION TYPES.

THERMAL EQUILIBRIUM DIAGRAMS OF BINARY ALLOYS. EFFECTS OF STRUCTURE ON

PHYSICAL PROPERTIES.

5. CAST IRON: GRADES, ALLOY CAST IRON, MALLEABLE IRON, S. G. IRON.

6. WROUGHT IRON: PROPERTIES AND USES.

7. STEEL: CLASSIFICATION OF STEELS, PROPERTIES AND USES, EFFECTS OF ALLOYING

METALS.

8. HEAT TREATMENT OF STEELS: STUDY OF HEAT-TREATMENT PROCESSES SUCH AS

NORMALIZING, ANNEALING, SPHEROIDIZING, HARDENING, TEMPERING, AUSTEMPERING,

MARTEMPERING, CASE-HARDENING, NITRIDING, CYANIDING, INDUCTION HARDENING,

FLAME-HARDENING, AGEING. APPLICATION OF ABOVE PROCESSES IN MECHANICAL

COMPONENTS SUCH AS GEARS, BEARING, TURBINE BLADES, CRANKSHAFTS, PISTONS,

CUTTING TOOL MATERIALS ALSO.

Subject

Code

Teaching Scheme Examination Scheme

Theory

Hrs

Pract

Hrs

Credits Exam

Theory

Paper

Theory

Marks Pract TW Total

Material

Science & Metallurgy

04 02 06

Sessional 1.5 Hrs 20

5 5 100 University 3 Hrs 70



9. NON-FERROUS ALLOYS: ALLOYS OF COPPER, ALUMINIUM, MAGNESIUM TITANIUM. OTHER

ALLOYS OF LEAD, TIN, ZINC, NICKEL, MANGANESE, WHITE METALS AND BEARING ALLOYS.

10. POWDER METALLURGY: APPLICATION AND ADVANTAGES, PRODUCTION OF POWDER,

COMPACTING, SINTERING, EQUIPMENT AND PROCESS CAPABILITY.

11. CORROSION OF METALS: MEANING, CAUSES AND NATURE. MEASURES OF

COUNTERACTING CORROSION, METAL COATINGS, ORGANIC COATINGS, LINING AND

CLADDING, USE OF CORROSION INHIBITORS, CATHODIC PROTECTION AGAINST

CORROSION.

12. NON-DESTRUCTIVE TESTING SUCH AS RADIOGRAPHY TESTING, DYE PENETRATION

TESTING, MAGNETIC PARTICLE TESTING, ULTRASONIC TESTING, AND JOMINY

ENDQUENCH TEST.

REFERENCE BOOKS:

1. ENGINEERING METALLURGY AND MATERIAL SCIENCE BY S. P. NAYAK.

2. MATERIALS AND METALLURGY BY G. B. S. NARANG AND K. MANCHANEDY

3. ELEMENTS OF METALLURGY BY DR. SWAROOP AND DR. SAXENA.

4. MATERIAL SCIENCE AND MANUFACTURING PROCESSS BY DHARMENDRAKUMAR AND S. K.

JAIN.

5. PHYSICAL METALLURGY BY ROBERT READ

6. METALLURGY FOR ENGINEERS BY V. RAGHVAN

7. METALLURGY FOR ENGINEERS BY BAVA.

8. PHYSICAL METALLURGY BY ROLLASON.

9. PHYSICAL METALLURGY BY HYEGINS.

10. TOOL STEEL BY RABERT.

11. MATERIAL SCIENCE BY ANNVER.

12. MATERIAL SCIENCE BY O.P. KHANNA.



PRACTICAL: 1

INTRODUCTION OF MATERIAL SCIENCE

DATE:

AIM: TO STUDY ABOUT BASICS OF MATERIAL SCIENCE AND METALLURGY.

Objective:

1. To know the importance of the materials.

2. To know about the Engineering requirements of material

3. To know the Various Properties of Engineering Material.

4. To Know the Criteria for the selection of the material.

Introduction:

Beginning of the Material Science - People began to make tools from stone Start

of the Stone Age about two million years ago. Natural materials ( stone, wood,

clay, skins, etc.) were used for different application.

The Stone Age ended about 5000 years ago with introduction of Bronze in the

Far East. Bronze is an alloy (a metal made up of more than one element) of ,

copper + < 25% of tin + other elements. Bronze: can be hammered or cast into a

variety of shapes, can be made harder by alloying, corrode only slowly after a

surface oxide film forms.

The Iron Age began about 3000 years ago and continues today. Use of iron and

steel, a stronger and cheaper material changed drastically daily life of a common

person.

Age of Advanced materials: throughout the Iron Age many new types of materials

have been introduced (ceramic, semiconductors, polymers, composites…).

Due to this much application it is necessary to understanding of the relationship

among structure, properties, processing, and performance of materials. And

based on that to develop intelligent design of new materials.



What is material Science?

Material science is the investigation of the relationship among processing, structure,

properties, and performance of materials.

Classification of materials:

Engineering Requirements of materials:

Engineering Requirements of a material means as what is expected from the material so

that the same can be success fully used for making engineering components. The main

engineering requirements of material fall under three categories:

Fabrication Requirements means that the material should be able to get

shaped easily. It is relate themselves with material’s machinability, ductility,

castability, heat treatability, weldability.

Service Requirements imply that the material selected for the purpose must

stand up to service demands, It is relate themselves with material’s Proper

Strength, wear resistance, corrosion resistance,etc.



Economic Requirements demand that the engineering part should be made

with minimum overall cost. Minimum overall cost may be achieved by Proper

selection of both technical and marketing variables.

Properties of Engineering Materials:

Properties are the way of the material responds to the environment and external forces.

Physical properties

Dimensions: Dimensions of a material implies its size(i.e. breadth, length,

diameter) and shap (i.e. Square,circular,channel,angle)

Appearance : Appearance includes lustre,colour and finish (e.g., line marks on

the surface) of a material.

Density : is the mass of unit volume of a material.

Melting point : is that temperature at which the solid metals changes into the

molten state.

Porosity: A material is said to be porous if it has pores within it. Pores can

absorb lubricant as in a sintered self – lubricating bearing.

Structure : Means geometric relationships of material components. it also implies

the arrangement of the internal components of matter.

Mechanical properties – response to mechanical forces, strength, etc.

Elasticity: The tendency of deformed solid to seek its original dimensions up on

unloading is called elasticity.

Young’s Modulus of Elas ticity E = Stress/Strain

Plasticity: is that property of a material by virtue of which it may be permanently

deformed when it has been subjected to an externally applied force great enough

to exceed the elastic limit.

Toughness: is the ability of the material to absorb energy during plastic

deformation up to fracture.

Resilience: is the capacity of a material to absorb energy when it is elastically

deformed and then upon unloading, to have this energy recovered.

Yield Strength: when metals are subjected to a tensile force, they stretch or

elongate as the stress increases. the point where the stretch suddenly increases,

is known as the yield strength of the material.



Tensile Strength: Tensile strength is the ability of a metal to resist being pulled

apart by opposing forces acting in a straight line.

Shear Strength: Shear strength is the ability of a metal fractured by opposing

forces not acting in to resist being a straight line.

Impact Strength : is the capacity of a material to resist or absorb shock energy

before it fracture .

Ductility : is the capacity of a material to undergo deformation under tension

without rupture. Or ability to drawn from a large section to a small section.

Malleability : is the capacity of a material to withstand deformation under

compression without rupture as for example in forging and rolling operations.

Brittleness : is defined as a tendency to fracture without appreciable deformation

and is therefore the opposite of ducti lity or malleability.

ST

RE

SS

STRAIN



Hardness : is the resistance of a material to plastic deformation usually by

indentation.

Fatigue : fatigue is the phenomenon that leads to fracture under fluctuating or

repeated loads.

Creep: is the time dependent permanent deformation that occurs under stress;

for most materials, it is important only at elevated temperatures.

Wear resistance: is the ability to resist wear and abrasion.

Compressive strength: Compressive strength is the ability of a metal to

withstand pressures acting on a given plane

Electrical and magnetic properties - response electrical and magnetic fields,

conductivity, etc.

Resistivity : it is a characteristic property of the material , due to which resists

the flow of electricity through it.

Conductivity : The reciprocal of electrical resistivity is called electrical

conductivity. Due to Which the electrical current flows easily through the material.

Dielectric strength : means the insulating capacity of a material against high

voltages.

Thermoelectricity : If two dissimilar metals are joined and this junction is then

heated, a small voltage in the millivolt range is produced and this is known as

thermoelectric effect.

Permeability : magnetic permeability measures the relative ease with which

magnetism may be developed in a material. And is the ratio of magnetic induction

to the intensity of magnetizing field.

Coercive force : This is the opposing magnetizing force which is necessary to

remove previous magnetization or residual magnetization.

Super conductivity : below certain temperature material becomes a perfect

diamagnetic material that is called super conductivity.

Thermal properties are related to transmission of heat and heat capacity.

Heat capacity : is the material’s ability to absorb heat from the external

surroundings.

Specific Heat : is the quantity of heat that must be added to a unit mass of the

solid to raise its temperature by one degree.



Thermal Expansion : When thermal energy is added to a material, a change in

its dimensions occurs, this phenomenon is called thermal expansion and property

of a material responsible for this is known as coefficient of thermal expansion.

Melting Point: Is the temperature at which a pure metal,compound,or eutectic

changes from solid to liquid; the temperature at which the liquid and the solid are

in equilibrium.

Thermal Conductivity: The rate at which heat can flow through a material under

the influence of a given temperature gradient is determined by the thermal

conductivity

Thermal Shock Resistance : defines the conditions of a body when it is

subjected to sudden and severe changes in temperature caused either by a

change in external environment or by internal heat generation. The ability of a

body to withstand such temperature changes without failure is called thermal

shock resistance.

Heat Resistance : is a general term referring to the ability of a material and its

properties to remain stable with changes in temperature.

Optical properties include to absorption, transmission and scattering of light.

Refractive Index: is the ration of the velocity of light in vacuum, to the velocity of

light within a material. And if angle of incidence i and the angle of refraction r then

it is equal to sin i / sin r

Absorptivity : Ability of a material to absorb the energy incidence.

Chemical stability in contact with the environment - corrosion resistance.

Corrosion Resistance :

Chemical Composition :

Acidity or Alkalinity :

Material Selection:

Material Selection Process:

1. Analysis of the materials application problem.(Performance requirements,

functional performance, physical attributes and application conditions.

2. Translation of the material application requirements to material properties values.

3. Selection of Candidate materials.

4. Evaluation of the candidate materials. This is parallel to Previous step.



Factors affecting a material selection:

• Properties of material

• Performance requirements

• Materials Reliability

• Safety

• Physical attributes

• Environment Conditions

• Availability

• Disposability and recyclability

• Economic Factors

Questions

1) Explain Material Selection Process for Crank Shaft.

2) Explain the Material Science’s Importance .

3) How the below Factors affecting a material Selection? Explain in Brief.

Properties of material

Performance requirements

Materials Reliability

Safety

Physical attributes

Environment Conditions

Availability

Disposability and recyclability

Economic Factors



PRACTICAL: 2

METALLIC MATERIALS

DATE:

AIM: TO STUDY ABOUT METALLIC MATERIALS.

Objective: To Know about the metallic material.

Introduction:

Classification of Metallic Materials:

Metal / alloys

Properties of Metallic Materials:

Melting temperature:

Density:

Thermal Conductivity:

Electrical Conductivity:



Tensile Strength:

Elasticity:









Relative electrical and thermal conductivities of some metals:

Thermal Properties of some important metals are:



Structure of material :

Metallic materials possess Crystal structure. Crystals possess a long-range order of

atomic arrangement through repeated periodicity at regular intervals in three dimensions

of space.

Every atom consists of a small nucleus composed of protons and neutrons, which

is encircled by moving electrons in their orbital, at specific energy levels.

In an atom, there will be always equal number of protons and electrons .

The top most orbital electrons, valence electrons, affect most material properties

that are of interest to engineer. E.g.: chemical properties, nature of bonding, size

of atom, optical/magnetic/electrical properties.

Electrons and protons are negative and positive charges of the same magnitude

being 1.60x10-19 coulombs.

Neutrons are electrically neutral.

Protons and neutrons have approximately the mass, 1.67x10-27kg, which is larger than

that of an electron, 9.11x10-31kg.



Principle types of Crystal Structure:

1. Body Centered Cubic

Example :

VANADIUM , MOLYBDENUM, TUNGSTEN , IRON( α ) , CHROMIUM(α )

2. Face centered Cubic

EXAMPLE :

COPPER, SILVER, GOLD, ALUMINIUM, LEAD, IRON (γ), CHROMIUM (β) ,COBALT

(β), NICKEL,PLATINUM .

3. Hexagonal Closed Packed



EXAMPLE :

BERYLLIUM, MAGNESIUM, ZINC, CADMIUM, COBALT (α)

Fracture:

• Fracture is the separation ,or fragmentation, of a solid body into two or more parts

under the action of stress.

• The process of fracture can be considered to be made up of two components,

crack initiation and crack propagation.

• Fracture can be classified into two general categories,

– Ductile fracture

– Brittle fracture

Spark Test:

• Spark testing is a method of determining the general classification of ferrous

materials. Normally it entails taking a piece of metal, usually scrap, and applying

it to a grinding wheel in order to observe the sparks emitted.

• These sparks can be compared to a chart or to sparks from a known test sample

to determine the classification. Spark testing also can be used to sort ferrous

materials, establishing the difference from one to another by noting if the spark is

the same or different .



(A) Wrought Iron , (B) Mild Steel , (C) Steel with 0.5 to 0.85% carbon , (D) High-

carbon tool steel ,(E) High-speed steel ,(F) Manganese steel ,(G) Mushet steel ,

(H) Special magnet steel

Fig.2.1 :Standard Chart of the sparks generated from the material

Chemical Analysis:

Bulk chemical analyses on metals and materials are available using the

following techniques:

• Optical Emission Spectroscopy

• Combustion (LECO) for C & S

• Atomic Absorption

- Surface analyses are available by SEM/EDS.

- Phase identification is available by X-ray Diffraction.

Test Sample Materials Detection Limits



Optical Emission

Spectroscopy

(OES)

Solid samples.

Min. diameter 12mm

Min. thickness

0.5mm

Iron, aluminium,

copper, nickel

and cobalt-based

alloys

>0.0002%, depending

on element and

sample.

Elements include:

Ag, Al, As, B, Bi, C,

Ca, Ce, Co, Cr, Cu,

Fe, Mg, Mn, Mo, N,

Nb, Ni, P, Pb, S, Sb,

Si, Sn, Te, Ti, V, W,

Zn, Zr.

Combustion

(LECO)

Solid samples,

turnings or powders.

Minimum weight 5g

Ferrous alloys C : 0.0002% to 10.0%

S : 0.0002% to 1.0%

Atomic

Absorption

Solid samples,

turnings, powders or

solutions.

Minimum weight 10g

Ferrous alloys

Non-ferrous

alloys

Inorganic

materials

>0.0005%, depending

on element and

sample.

Elements include:

Ag, Al, As, B, Be, Bi,

Ca, Cd, Ce, Co, Cr,

Cu, Fe, Mg, Mn, Mo,

Nb, Ni, Pb, Sb, Si, Se,

Sn, Sr, Ta, Te, Ti, V,

W, Zn, Zr.

SEM/EDS Solid samples or

powders.

Very small samples

possible.

Ferrous alloys

Non-ferrous

alloys

Inorganic

materials

>0.1%, depending on

element and sample.

Elements with atomic

number ≥ 5

X-ray Diffraction Solid samples or

powders.

Crystalline solids >1.0%, depending on

phase and sample.



Questions



PRACTICAL: 3

EFFECTS OF ALLOYING

DATE:

Aim: TO STUDY ABOUT THE EFFECTS OF ALLOYING METALS.

Objective:

To know the effects of alloying elements on the steel properties.

Introduction:

Alloying elements have significant effect on the iron-iron carbide equilibrium diagram.

The addition of some of these alloying elements will widen the temperature range

through which austenite (g -iron) is stable while other elements will constrict the

temperature range. What this means is that some elements will raise and some

elements will lower the critical temperature of steel.

Manganese, cobalt, and nickel increase the temperature range through which austenite

is stable. This also means that the lower critical temperature of steel will be lowered by

these alloying elements. Other alloying elements that lower the critical temperature of

steel are carbon, copper and zinc. The alloying elements that are used to reduce the

critical temperature are highly soluble in the gamma iron (austenite). Figure 3.1 shows

the effect of manganese on the critical temperature of steel.



Figure 3.1 The effect of alloying with manganese on the critical temperature of steel and

austenite (g -iron) phase transformation zone on the iron-iron carbide diagram..

Alloys such as aluminum, chromiuim, molybdenum, phosphorus, silicon, tungsten tend

to form solid solutions with alpha iron (ferrite). This constricts the temperature region

through which gamma iron (austenite) is stable. As shown in Figure 3.2, chromium at

different percentages constricts the critical temperature range which results in a marked

reduction of the region where austenite is stable.

Figure 3.2 Effect of alloying with chromium on the critical temperature of steel and

austenite (g -iron) phase transformation zone on the iron-iron carbide diagram.



The elements shown in Figure 3 have the greatest solubility in ferrite and also influence

the hardenability of iron when in the presence of carbon. With a slight increase in the

carbon content, they respond markedly to heat treating, because carbon acts as a ferrite

strengthener. As indicated in Figure 3.3, Phosphorus will improve the hardness of the

ferrite significantly by adding only a very small percentage of Phosphorus, while

Chromium will not strengthen the ferrite that well even at very high percentage of

Chromium addition to the steel.

Figure 3.3 The effect of various alloying elements on the hardness of steel.

Figure 3.4 shows the effect of furnace cooling vs. air cooling on the tensile strength of

steel for three different percentages of carbon in the p resence of chromium. As this

figure indicates, furnace cooling has very little effect on the tensile strength of the

material. The addition of chromium does not change the tensile strength properties

when the steel is cooled in the furnace. If the same steels are air cooled at the same

rate, the slope of the curves increases significantly which means that a slight increase in

the chromium content increases the strength drastically when air cooling is applied.



Figure 3.4 Effect of different percentages of carbon on the tensile strength of steel in the

presence of chromium.

Effect of Carbon on Physical Properties:

In general, as the carbon content increases the hardness of the steel also increases.

The tensile strength and the yield strength also increase to about 0.83 % carbon.

Thereafter, they level out. This is shown in Figure 3.5.

Figure 3.5 Effect of carbon on hardness, tensile strength and yield

strength of steels.



The tensile strength and hardness are affected as the ratio of ferrite to cementite in the

structure of steel changes. As the percentage of pearlite increases in the hypoeutectoid

steels, the tensile strength increases. The hardness does not increase dramatically. The

hypereutectoid steels show only a slight increase in strength as the cementite-to-ferrite

ratio increases.

The elongation and the reduction in area represent how ductile or brittle a material is.

Figure 3.6 indicates the effect of carbon on the ductility and impact resistance

(toughness) of steels. The elongation and the reduction in area drop sharply with

increase in carbon content, going almost to zero at about 1.5 % carbon. This indicates

that the carbon content of 1.5 % or more will cause high brittleness. The impact

resistance also decreases very sharply up to about 0.83 % carbon and then levels out.

Figure 3.6 Effect of carbon on the impact resistance and ductility of steels.

Questions



PRACTICAL: 4

MACRO EXAMINATION AND MICRO EXAMINATION

DATE:

Aim: TO PREPARE SPECIMEN FOR MACRO EXAMINATION AND MICRO EXAMINATION

Objective:

To study procedure of specimen preparation for macroscopic & microscopic

examination.

Introduction:

A little can be learned regarding the structural characteristics of a metal by microscopic

examination unless the surface that is to be examined is first prepared according to

more or less rigid and precise procedures. With the use of modern metallurgical

microscope and precision optical parts where the obtainable resolution may be as great

as a fraction of the wavelength of the light used to illuminate the specimen, it is evident

that perfect specimen preparation is of the greatest importance.

Improper preparation is likely to remove all important inclusions, erode grain boundaries

of temper hardened steel specimens, ultimately producing a structure, superficially at

least, which upon micro-examination will appear entirely different from that which is truly

representative and characteristic of metal. Obviously an examination of such a prepared

specimen will lead only to erroneous interpretations and unreliable conclusions.

Practical Contents:

1. Determine the appropriate location and orientation of the specimen to be cut.

2. Mounting the specimen if required.

3. If the specimen to be observed is too uneven, or with burrs etc. achieve plane

surface by either filling or grinding on coarse grade emery paper.



4. Take emery papers from coarse to finer abrasive grid (i.e 1/0, 2/0, 3/0 & 4/0). The

emery is placed on any clean, hard, level surface. The specimen is rubbed back

and forth across the entire length of paper under moderately applied pressure.

While being ground, the specimen is held so that the new, finer scratches being

introduced on the surface are approximately at right angles to the old scratches

resulting from previous flattening operation. Switch over to next finer grade and

repeat the same procedure.

5. Now for better surface finish go to the polishing wheel. The polishing wheel

mounted cloth is rotated at appropriate speed and the specimen is moved

continuously from the center to the periphery of the polishing wheel with

moderate pressure.

6. Select suitable etchant for the specimen and carry out the etching.

7. Immediately after etching, wash the specimen under running water and dry it with

alcohol.

8. Set the microscope with suitable selection of eye piece and objective for the

desired magnification.

Macro examination:

Useful information about the structure of a piece of metal can often be obtained without

the aid of a microscope. Such investigation is usually referred to as 'macro-examination'

and it may be carried out with the naked eye or by using a small hand magnifying lens.

Fig. 4.1 Macrograph of a specimen



Micro examination:

In micro examination the material is examined at the atomic level by using the electron

microscope at high magnification to get the structure details of the same material.

Fig. 4.2 Micro graph of a specimen

Macro etching reagents:



Questions

1) What is metallography? Briefly explain its importance in Metallurgy.

2) What is the basic difference between low grade no. emery paper and high grade

no. emery paper in the intermediate polishing process?

3) What is an etchant? Why etching is required? List at least three name of etchant

used for different material.

4) List the instruments and accessories you have used for preparing the sample

along with their specification details.



PRACTICAL: 5

MICRO EXAMINATION OF STANDARD SPECIMEN

DATE:

Aim: TO PERFORM MICRO EXAMINATION OF STANDARD SPECIMEN

Objective:

To understand procedure and relevance of Micro-Examination.

Introduction:

Micro examination is study of internal structure of a material i.e. microstructure, which

can be carried out by light microscopy or electron microscopy. An observation of

microstructure in a microscope will show size and shape of grains and the size, shape

and distribution of various phases and inclusions and segregations. These structural

characteristics have great effect on mechanical properties of a material. The

microstructure will reveal the mechanical and thermal treatment of the material and it

may be possible to predict the expected behavior under a given set of conditions.

Practical Contents:

1) Select the etchant required as per the specimen.

2) Carry out etching

3) Immediately after etching, wash the specimen under running water and dry it with

alcohol.

4) Set the microscope with suitable selection of eye piece and objective for the

desired magnification.

5) Sketch the microstructure observed.

Questions:

1) Record the microstructure observed in microscope with the aid of schematic

diagram.

2) Explain the impact of microstructure on various properties of materials



PRACTICAL: 6

IRON CARBON DIAGRAM & ALLOTROPY OF IRON

DATE:

AIM: TO STUDY ABOUT IRON CARBON DIAGRAM & ALLOTROPY OF IRON.

Objective:

(1) To understand Iron Carbon Diagram & its application.

(2) To know the allotropy of iron.

Iron Carbon Diagram

A study of iron-carbon system is useful and important in many respects. This is

because (1) steels constitute greatest amount of metallic materials used by man (2)

solid state transformations that occur in steels are varied and interesting. These are

similar to those occur in many other systems and helps explain the properties.

Iron-carbon phase diagram shown in figure-6.1 is not a complete diagram. Part of

the diagram after 6.67 wt% C is ignored as it has little commercial significance. The

6.67%C represents the composition where an inter-metallic compound, cementite

(Fe3C), with solubility limits forms. In addition, phase diagram is not true equilibrium

diagram because cementite is not an equilibrium phase. However, in ordinary steels

decomposition of cementite into graphite never observed because nucleation of

cementite is much easier than that of graphite. Thus cementite can be treated as an

equilibrium phase for practical purposes.

The Fe-Fe3C is characterized by five individual phases and four invariant

reactions. Five phases that exist in the diagram are: α–ferrite (BCC) Fe-C solid solution,

γ-austenite (FCC) Fe-C solid solution, δ-ferrite (BCC) Fe-C solid solution, Fe3C (iron

carbide) or cementite - an inter-metallic compound and liquid Fe-C solution. Four

invariant reactions that cause transformations in the system are namely eutectoid,

eutectic, monotectic and peritectic.



Figure 6.1: Iron – Iron carbide phase diagram.

As depicted by left axes, pure iron upon heating exhibits two allotropic changes.

One involves α–ferrite of BCC crystal structure transforming to FCC austenite, γ-iron, at

. t C, austenite changes to BCC phase known as δ-ferrite, which finally

melts at 5 C.

Carbon present in solid iron as interstitial impurity, and forms solid solution with

ferrites / austenite as depicted by three single fields represented by α, γ and δ. Carbon

dissolves least in α–ferrite in which maximum amount of carbon soluble is . at

C. This limited solubility is attributed to shape and size of interstitial position in BCC α–

ferrite. However, carbon present greatly influences the mechanical properties of α–

ferrite. α–ferrite can be used as magnetic material below C. Solubility of carbon in

γ-iron reaches its maximum, 2.11%, at a temperature of 1147 C. Higher solubility of

carbon in austenite is attributed to FCC structure and corresponding interstitial sites.

Phase transformations involving austenite plays very significant role in heat treatment of



different steels. Austenite itself is non-magnetic. Carbon solubility in δ-ferrite is

maximum ( . ) at 5 C. As this ferrite exists only at elevated temperatures, it is of

no commercial importance. Cementite, Fe3C an inter-metallic compound forms when

amount of carbon present exceeds its solubility limit at respective temperatures. Out of

these four solid phases, cementite is hardest and brittle that is used in different forms to

increase the strength of steels. α–ferrite, on the other hand, is softest and act as matrix

of a composite material. By combining these two phases in a solution, a material’s

properties can be varied over a large range.

For technological convenience, based on %C dissolved in it, a Fe-C solution is

classified as: commercial pure irons with less than 0.008%C; steels having %C between

0.008-2.11; while cast irons have carbon in the range of 2.11%-6.67%. Thus commercial

pure iron is composed of exclusively α–ferrite at room temperature. Most of the steels

and cast irons contain both α–ferrite and cementite. However, commercial cast irons are

not simple alloys of iron and carbon as they contain large quantities of other elements

such as silicon, thus better consider them as ternary alloys. The presence of Si

promotes the formation of graphite instead of cementite. Thus cast irons may contain

carbon in form of both graphite and cementite, while steels will have carbon only in

combined from as cementite.

As shown in figure-6.1, and mentioned earlier, Fe-C system constitutes Five phases and

four invariant reactions:

CEMENTITE (Fe3C):

Cementite is also known as iron carbide which has a chemical formula, Fe3C. It contains

6.67 % Carbon by weight. It is a typical hard and brittle interstitial compound of low

tensile strength (approximately 5,000 psi) but high compressive strength. Its crystal

structure is orthorhombic.

AUSTENITE (g iron):

It is also known as (g ) gamma-iron, which is an interstitial solid solution of carbon

dissolved in iron with a face centered cubic crystal (F.C.C) structure. Austenite is

normally unstable at room temperature. Under certain conditions it is possible to obtain

austenite at room temperature. Average properties of austenite are:



Tensile strength 150,000 psi.

Elongation 10 % in 2 in gage length.

Hardness Rockwell C 40

Toughness High

Table 6.1 Properties of Austenite

Figure 6.2 Austenite (gamma iron) crystal structure

FERRITE (a iron):

Figure 6.3 Ferrite (alpha iron) crystal structure

It is also known as (a ) alpha -iron, which is an interstitial solid solution of a small

amount of carbon dissolved in iron with a Body Centered Cubic (B.C.C.) crystal

structure. It is the softest structure on the iron-iron carbide diagram. Average properties

are:



Tensile Strength 40,000 psi

Elongation 40 % in 2 in gage length

Hardness Less than Rockwell C 0 or less than Rockwell B 90.

Toughness Low

Table 6.2 Properties of Ferrite.

PEARLITE (a + Fe3C)

It is the eutectoid mixture containing 0.83 % Carbon and is formed at 1333oF on very

slow cooling. It is very fine plate like or lamellar mixture of ferrite and cementite. The

structure of pearlite includes a white matrix (ferritic background) which includes thin

plates of cementite. Average properties are:

Tensile Strength 120,000 psi

Elongation 20 % in 2 in gage length

Hardness Rockwell C 20 or BHN 250-300

Table 6.3 Properties of pearlite.

Figure 6.4 Pearlite microstructure (Light background is the ferrite matrix, dark lines are the cementite network)

LEDEBURITE (a + Fe3C)

It is the eutectic mixture of austenite and cementite. It contains 4.3 % Carbon and

represents the eutectic of cast iron. Ledeburite exists when the carbon content is greater



than 2 %, which represents the dividing line on the equilibrium diagram between steel

and cast iron.

(d ) DELTA IRON:

Delta iron exists between 2552 and 2802 oF. It may exist in combination with the melt to

about 0.50 % Carbon, in combination with austenite to about 0.18 % Carbon and in a

single phase state out to about 0.10 % carbon. Delta iron has the Body Centered Cubic

(B.C.C) crystal structure and is magnetic.

- peritectic reaction at 5 C and 0.16%C,

δ-ferrite + L ↔ γ-iron (austenite)

- monotectic reaction 5 C and 0.51%C,

L ↔ L + γ-iron (austenite)

- eutectic reaction at C and 4.3 %C,

L ↔ γ-iron + Fe3C (cementite) [ledeburite]

- eutectoid reaction at C and 0.8%C,

γ-iron ↔ α–ferrite + Fe3C (cementite) [pearlite]

Product phase of eutectic reaction is called ledeburite, while product from

eutectoid reaction is called pearlite. During cooling to room temperature, ledeburite

transforms into pearlite and cementite. At room temperature, thus after equilibrium

cooling, Fe-C diagram consists of either α–ferrite, pearlite and/or cementite. Pearlite is

actually not a single phase, but a micro-constituent having alternate thin layers of α–

ferrite (~88%) and Fe3C, cementite (~12%). Steels with less than 0.8%C (mild steels up

to 0.3%C, medium carbon steels with C between 0.3%-0.8% i.e. hypo-eutectoid Fe-C

alloys) i.e. consists pro-eutectoid α–ferrite in addition to pearlite, while steels with carbon

higher than 0.8% (high-carbon steels i.e. hyper-eutectoid Fe-C alloys) consists of

pearlite and pro-eutectoid cementite. Phase transformations involving austenite i.e.

processes those involve eutectoid reaction are of great importance in heat treatment of

steels.

In practice, steels are almost always cooled from the austenitic region to room

temperature. During the cooling upon crossing the boundary of the single phase γ-iron,



first pro-eutectoid phase (either α–ferrite or cementite) forms up to eutectoid

temperature. With further cooling below the eutectoid temperature, remaining austenite

decomposes to eutectoid product called pearlite, mixture of thin layers of α–ferrite and

cementite. Though pearlite is not a phase, nevertheless, a constituent because it has a

definiteappearance under the microscope and can be clearly identified in a structure

composed of several constituents. The decomposition of austenite to form pearlite

occurs by nucleation and growth. Nucleation, usually, occurs heterogeneously and

rarely homogeneously at grain boundaries. When it is not homogeneous, nucleation of

pearlite occurs both at grain boundaries and in the grains of austenite. When austenite

forms pearlite at a constant temperature, the spacing between adjacent lamellae of

cementite is very nearly constant. For a given colony of pearlite, all cementite plates

have a common orientation in space, and it is also true for the ferrite plates. Growth of

pearlite colonies occurs not only by the nucleation of additional lamellae but also

through an advance at the ends of the lamellae. Pearlite growth also involves the

nucleation of new colonies at the interfaces between established colonies and the

parent austenite. The thickness ratio of the ferrite and cementite layers in pearlite is

approximately 8 to 1. However, the absolute layer thickness depends on the

temperature at which the isothermal transformation is allowed to occur.

The temperature at which austenite is transformed has a strong effect on the

inter-lamellar spacing of pearlite. The lower the reaction temperature, the smaller will be

inter-lamellar spacing. For example, pearlite spacing is in order of 10-3 mm when it

formed at , while spacing is in order of - mm when formed at C. The

spacing of the pearlite lamellae has a practical significance because the hardness of the

resulting structure depends upon it; the smaller the spacing, the harder the metal. The

growth rate of pearlite is also a strong function of temperature. t temperatures ust

below the eutectoid, the growth rate increases rapidly with decreasing temperature ,

reaching a maximum at C, and then decreases again at lower temperatures.

Additions of alloying elements to Fe-C system bring changes (alternations to

positions of phase boundaries and shapes of fields) depends on that particular element

and its concentration. Almost all alloying elements causes the eutectoid concentration to

decrease, and most of the alloying elements (e.g.: Ti, Mo, Si, W, Cr) causes the

eutectoid temperature to increase while some other (e.g.: Ni, Mn) reduces the eutectoid



temperature. Thus alloying additions alters the relative amount of pearlite and pro-

eutectoid phase that form.

Fe-C alloys with more than 2.11% C are called cast irons. Phase transformations in cast

irons involve formation of pro-eutectic phase on crossing the liquidus. During the further

cooling, liquid of eutectic composition decomposes in to mixture of austenite and

cementite, known as ledeburite. On further cooling through eutectoid temperature,

austenite decomposes to pearlite. The room temperature microstructure of cast irons

thus consists of pearlite and cementite. Because of presence of cementite, which is

hard, brittle and white in color, product is called white cast iron. However, depending on

cooling rate and other alloying elements, carbon in cast iron may be present as graphite

or cementite. Gray cast iron contains graphite in form of flakes. These flakes are sharp

and act as stress risers. Brittleness arising because of flake shape can be avoided by

producing graphite in spherical nodules, as in malleable cast iron and SG (spheroidal

graphite) cast iron. Malleable cast iron is produced by heat treat ing white cast iron (Si

) for prolonged periods at about C and then cooling it very slowly. The

cementite decomposes and temper carbon appears approximately as spherical

particles. SG iron is produced by adding inoculants to molten iron. In these Si content

must be about 2.5%, and no subsequent heat treatment is required.

Allotropy of Iron

Polymorphism is a physical phenomenon where a material may have more than one

crystal structure. A material that shows polymorphism exists in more than one type of

space lattice in the solid state. If the change in structure is reversible, then the

polymorphic change is known as allotropy. The prevailing crystal structure depends on

both the temperature and the external pressure.

One familiar example is found in carbon: graphite is the stable polymorph at ambient

conditions, whereas diamond is formed at extremely high pressures.

The best known example for allotropy is iron. There are three allotropic forms of iron,

known as alpha, gamma, and delta.

As molten iron cools down it crystallizes at 1538°C into its delta allotrope, which has a

body-centred cubic (BCC) crystal structure. As it cools further its crystal structure

http://en.wikipedia.org/wiki/Body-centred_cubic

http://en.wikipedia.org/wiki/Crystal_structure



changes to face centred cubic (FCC) at 1394°C, when it is known as gamma-iron, or

austenite. At 912°C the crystal structure again becomes BCC as alpha -iron also known

as ferrite, is formed, and at 770°C (the Curie point, Tc ) the iron becomes magnetic as

alpha-iron, which is also BCC, is formed. As the iron passes through the Curie

temperature there is no change in crystalline structure, but there is a change in the

magnetic properties

Figure 6.5. Cooling curve for pure iron. (Allotropic behavior of pure iron)

a -iron (alpha) :

Figure 6.6 Alpha iron (B.C.C) unit cell

The other name for a -iron is ferrite. This crystal has body centered cubic structure. The

unit cell and the micrograph of the crystal are shown in Figures (6.6) and (6.7).

http://en.wikipedia.org/wiki/Face_centred_cubic

http://en.wikipedia.org/wiki/Austenite

http://en.wikipedia.org/wiki/Ferrite_(iron)

http://en.wikipedia.org/wiki/Curie_point

http://en.wikipedia.org/wiki/Magnetic



Figure 6.7 Ferrite crystals.

g -iron (Gamma):

Figure 6.8 Face centered cubic crystal unit cell.

The other name for g -iron is austenite. This crystal has face centered cubic (F.C.C)

structure. The unit cell and the micrograph of the crystal are shown in Figures (6.8) and (6.9).

Figure 6.9 Austenite crystals.



Questions



PRACTICAL: 7

CAST IRON

DATE:

Aim: TO STUDY ABOUT CAST IRON.

Objective:

(1) To know the various types of Cast irons.

(2) To know Properties of Cast Iron.

Introduction:

Cast iron usually refers to grey iron, but also identifies a large group of ferrous alloys,

which solidify with a eutectic. The colour of a fractured surface can be used to identify

an alloy. White cast iron is named after its white surface when fractured, due to its

carbide impurities which allow cracks to pass straight through. Grey cast iron is named

after its grey fractured surface, which occurs because the graphitic flakes deflect a

passing crack and initiate countless new cracks as the material breaks.

Iron (Fe) accounts for more than 95% by weight (wt%) of the alloy material, while the

main alloying elements are carbon (C) and silicon (Si). The amount of carbon in cast

irons is 2.1 to 4 wt%. Cast irons contain an appreciable amount of silicon, normally 1 to

3 wt%, and consequently, these alloys should be considered ternary Fe-C-Si alloys.

Types of Cast Iron

(1) Grey cast iron :

Grey cast iron is characterized by its graphitic microstructure, which causes fractures of

the material to have a grey appearance. It is the most commonly used cast iron and the

most widely use cast material base on weight. Most cast irons have a chemical

composition of 2.5 to 4.0% carbon, 1 to 3% silicon, and the remainder is iron. Grey cast

iron has less tensile strength and shock resistance than steel, however its compressive

strength is comparable to low and medium carbon steel.

http://en.wikipedia.org/wiki/Gray_iron

http://en.wikipedia.org/wiki/Ferrous

http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Eutectic

http://en.wikipedia.org/wiki/Carbide

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Wt%25

http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Silicon

http://en.wikipedia.org/wiki/Tensile_strength

http://en.wikipedia.org/wiki/Shock_resistance

http://en.wikipedia.org/wiki/Compressive_strength

http://en.wikipedia.org/wiki/Compressive_strength



(2) White cast iron:

With a lower silicon content and faster cooling, the carbon in white cast iron precipitates

out of the melt as the metastable phase cementite, Fe3C, rather than graphite. The

cementite which precipitates from the melt forms as relatively large particles, usually in a

eutectic mixture, where the other phase is austenite (which on cooling might transform

to martensite). These eutectic carbides are much too large to provide precipitation

hardening (as in some steels, where cementite precipitates might inhibit plastic

deformation by impeding the movement of dislocations through the ferrite matrix).

Rather, they increase the bulk hardness of the cast iron simply by virtue of their own

very high hardness and their substantial volume fraction, such that the bulk hardness

can be approximated by a rule of mixtures. In any case, they offer hardness at the

expense of toughness. Since carbide makes up a large fraction of the material, white

cast iron could reasonably be classified as a cermet. White iron is too brittle for use in

many structural components, but with good hardness and abrasion resistance and

relatively low cost, it finds use in such applications as the wear surfaces (impeller and

volute) of slurry pumps, shell liners and lifter bars in ball mills and autogenous grinding

mills, balls and rings in coal pulverisers, and the teeth of a backhoe's digging bucket

(although cast medium-carbon martensitic steel is more common for this application).

White cast iron can also be made by using a high percentage of chromium (Cr) in the

iron; Cr is a strong carbide-forming element, so at high enough percentages of chrome,

the precipitation of graphite out of the iron is suppressed. High-chrome white iron alloys

allow massive castings (for example, a 10-tonne impeller) to be sand cast, i.e., a high

cooling rate is not required, as well as providing impressive abrasion resistance.

(3) Malleable cast iron :

Malleable iron starts as a white iron casting, that is then heat treated at about 900 °C

(1,650 °F). Graphite separates out much more slowly in this case, so that surface

tension has time to form it into spheroidal particles rather than flakes. Due to their lower

aspect ratio, spheroids are relatively short and far from one another, and have a lower

cross section vis-a-vis a propagating crack or phonon. They also have blunt boundaries,

as opposed to flakes, which alleviates the stress concentration problems faced by grey

http://en.wikipedia.org/wiki/Metastable

http://en.wikipedia.org/wiki/Cementite

http://en.wikipedia.org/wiki/Austenite

http://en.wikipedia.org/wiki/Martensite

http://en.wikipedia.org/wiki/Plastic_deformation

http://en.wikipedia.org/wiki/Plastic_deformation

http://en.wikipedia.org/wiki/Dislocation

http://en.wikipedia.org/wiki/Hardness

http://en.wikipedia.org/wiki/Toughness

http://en.wikipedia.org/wiki/Cermet

http://en.wikipedia.org/wiki/Impeller

http://en.wikipedia.org/wiki/Volute_(disambiguation)

http://en.wikipedia.org/w/index.php?title=Slurry_pump&action=edit&redlink=1

http://en.wikipedia.org/w/index.php?title=Lifter_bar&action=edit&redlink=1

http://en.wikipedia.org/wiki/Ball_mill

http://en.wikipedia.org/w/index.php?title=Autogenous_grinding_mill&action=edit&redlink=1

http://en.wikipedia.org/w/index.php?title=Autogenous_grinding_mill&action=edit&redlink=1

http://en.wikipedia.org/w/index.php?title=Coal_pulveriser&action=edit&redlink=1

http://en.wikipedia.org/wiki/Backhoe

http://en.wikipedia.org/wiki/Chromium

http://en.wikipedia.org/wiki/Heat_treatment

http://en.wikipedia.org/wiki/Surface_tension

http://en.wikipedia.org/wiki/Surface_tension

http://en.wikipedia.org/wiki/Aspect_ratio

http://en.wikipedia.org/wiki/Cross_section_(geometry)



cast iron. In general, the properties of malleable cast iron are more like mild steel. There

is a limit to how large a part can be cast in malleable iron, since it is made from white

cast iron.

(3) Ductile cast iron :

A more recent development is nodular or ductile cast iron . Tiny amounts of magnesium

or cerium added to these alloys slow down the growth of graphite precipitates by

bonding to the edges of the graphite planes. Along with careful control of other elements

and timing, this allows the carbon to separate as spheroidal particles as the material

solidifies. The properties are similar to malleable iron, but parts can be cast with larger

sections.

Table 7.1 Comparative qualities of cast irons

NAME

NOMINAL

COMPOSITIO

N [% BY

WEIGHT]

FORM AND

CONDITIO

N

YIELD

STRENGT

H [KSI

(0.2%

OFFS ET)]

TENSILE

STRENGT

H [KSI]

ELONGATIO

N [% (IN

2 INCHES)]

HARDNES

S

[BRINELL

SCALE]

USES

GREY

CAST IRON

(ASTM

A48)

C 3.4, SI 1.8, MN 0.5

CAST — 25 0.5 180

ENGINE

CYLINDER

BLOCKS,

FLYWHEELS, GEARS,

MACHINE-TOOL BASES

WHITE

CAST IRON

C 3.4, SI 0.7, MN 0.6

CAST (AS

CAST) — 25 0 450

BEARING

SURFACES

MALLEABL

E IRON

(ASTM

A47)

C 2.5, SI 1.0, MN 0.55

CAST

(ANNEALE

D)

33 52 12 130

AXLE

BEARINGS,

TRACK

WHEELS, AUTOMOTIV

E

CRANKSHAF

TS

DUCTILE

OR

NODULAR

IRON

C 3.4, P 0.1,

MN 0.4, NI 1.0, MG 0.06

CAST 53 70 18 170

GEARS,

CAMSHAFTS, CRANKSHAF

TS

http://en.wikipedia.org/wiki/Magnesium

http://en.wikipedia.org/wiki/Cerium

http://en.wikipedia.org/wiki/Pounds_per_square_inch

http://en.wikipedia.org/wiki/Brinell_scale

http://en.wikipedia.org/wiki/Brinell_scale

http://en.wikipedia.org/wiki/ASTM_International

http://en.wikipedia.org/wiki/Manganese

http://en.wikipedia.org/wiki/Internal_combustion_engine

http://en.wikipedia.org/wiki/Flywheel

http://en.wikipedia.org/wiki/Gear

http://en.wikipedia.org/wiki/Bearing_(mechanical)

http://en.wikipedia.org/wiki/Axle

http://en.wikipedia.org/wiki/Crankshaft

http://en.wikipedia.org/wiki/Crankshaft

http://en.wikipedia.org/wiki/Nickel

http://en.wikipedia.org/wiki/Camshaft



DUCTILE

OR

NODULAR

IRON

(ASTM

A339)

— CAST

(QUENCH

TEMPERED)

108 135 5 310 —

NI-HARD

TYPE 2

C 2.7, SI 0.6, MN 0.5,

NI 4.5, CR 2.0

SAND-

CAST — 55 — 550

HIGH

STRENGTH

APPLICATIO

NS

NI-RESIST

TYPE 2

C 3.0, SI 2.0, MN 1.0,

NI 20.0, CR 2.5

CAST — 27 2 140

RESISTANCE

TO HEAT

AND

CORROSION

Questions



PRACTICAL:8

HEAT TREATMENT

DATE:

Aim: TO STUDY ABOUT HEAT TREATMENT

Objectives:

(1) To know the importants of Heat Treatments.

(2) To Know various types of Heat Treatments.

(3) To show the effect of different quenching media (Oil, water and Brine) on the

hardness of specimens of same composition.

Introduction:

As a result of cold working, the hardness, tensile strength, and electrical resistance

increase, while ductility decreases. There is also a large increase in the number of

dislocations, and certain planes in the crystal structure are severely distorted. Most of

the energy used to cold work the metal is dissipated in heat, and a finite amount of

energy is stored in the crystal structure as internal energy associated with the lattice

defects created by the deformation.

Various types of heat treatment processes are used to change the following properties

or conditions of the steel:

Improve the toughness

Increase the hardness

Increase the ductility

Improve the machinability

Refine the grain structure

Remove the residual stresses

Improve the wear resistance



The following are the general reasons for heat treatment:

Hardening

Steels can be heat treated to high hardness and strength levels. The reasons for doing

this are obvious. Structural components subjected to high operating stress need the high

strength of a hardened structure. Similarly, tools such as dies, knives, cutting devices,

and forming devices need a hardened structure to resist wear and deformation.

Tempering

As-quenched hardened steels are so brittle that even slight impacts may cause fracture.

Tempering is a heat treatment that reduces the brittleness of a steel without significantly

lowering its hardness and strength. All hardened steels must be tempered before use.

Softening a Hardened Structure

Hardening is reversible. If a hardened tool needs to be remachined, it may be softened

by heat treatment to return it to its machinable condition. Most steels weld better in their

soft state than in their hardened state; softening may be used to aid weldability.

Recrystallization

If a metal is cold worked, grains or crystals deform, become elongated, and in doing so

harden and strengthen a metal. There is a limiting amount of cold work that a particular

metal can be subjected to. In rolling of steel into thin sheets, you can only reduce the

cross-sectional area so much before it gets too hard to roll. At this point it would be

desirable to return the grains to their original shape. Heat treatment can accomplish this.

The transformation of cold-worked grains to an undistorted shape is called

recrystallization. Very large coarse grains can also be refined by recrystallization.This

type of heat treatment is essential if a steel is to be subjected to severe cold working in

rolling, drawing, etc.

Stress Relief

One of the most frequent reasons for heat treatment is to remove internal stress from a

metal that has been subjected to cold working or welding. Stress relieving is a heat



treatment used to remove internal strains without significantly lowering the strength. It is

used where close dimensional control is needed on weldments, forgings, castings, etc.

Hot-Working Operations

Most metal shapes produced by steel mills are at least rough shaped at elevated

temperatures. Heat treating is required to bring the rough metal shapes to the proper

temperature for hot-forming operations. Forging, hot rolling, roll welding, and the like are

all performed at temperatures of sufficient magnitude as to prevent the formation of

distorted grains that will harden the metals. Hot-working operations require dynamic

recrystallization which is achieved by working at the proper hot-work temperatures.

Diffusion of Alloying Elements

One of the criteria for hardening a steel is that it have sufficient carbon content. Low

carbon steels can be hardened, at least on the surface, by heat treating at an elevated

temperature in an atmosphere containing an alloying element that will diffuse into the

steel and allow surface hardening on quenching. Carbon is frequently diffused into the

surface of soft steels for surface hardening. Using this same principle, elements such as

chromium, boron, nitrogen, and silicon can be diffused in the surface of steel for special

purposes.

Figure 8.1 Types of Heat Treatment



Full Annealing:

Full annealing is the process by which the distorted cold worked lattice structure is

changed back to one which is strain free through the application of heat. This process is

carried out entirely in the solid state and is usually followed by slow cooling in the

furnace from the desired temperature. The annealing process may be divided into three

stages:

Recovery

Recrystallization

Grain growth

Recovery:

This is primarily a low temperature process, and the property changes produced do not

cause appreciable change in microstructure or the properties, such as tensile strength,

yield strength, hardness and ductility. The principal effect of recovery is the relief of

internal stresses due to cold working.

When the load which causes plastic deformation is released, all the elastic deformation

does not disappear. This is due to the different orientation of crystals, which will not

allow some of them to move back when the load is released. As the temperature is

increased, there is some spring back of these elastically displaced atoms which relieve

most of the internal stresses. Electrical conductivity is also increased appreciably during

the recovery stage.

Since the mechanical properties of the metal are essentially unchanged, the main

purpose of heating in the recovery range is stress relieving cold worked alloys to prevent

stress corrosion cracking or to minimize the distortion produced by residual stresses.

Commercially, this low temperature treatment in the recovery range is known as stress

relief annealing or process annealing.

Recrystallization:

As the temperature of the recovery range is reached, minute new crystals appear in the

microstructure. These new crystals have the same composition and lattice structure as



the original undeformed grains and are not elongated but are uniform in dimensions.

The new crystals generally appear at the most drastically deformed portions of the grain,

usually the grain boundaries and slip planes. The cluster of atoms from which the new

grains are formed is called a nucleus. Recrystallization takes place by a combination of

nucleation of strain free grains and the growth of these nuclei to absorb the entire cold

worked material.

The term recrystallization temperature does not refer to a definite temperature below

which recrystallization will not occur, but refers to the approximate temperature at which

a highly cold worked material completely recrystallizes in one hour. The recrystallization

temperatures of several metals and alloys are listed in following table.

Material Recrystallization

Temperature (oF)

Copper ( 99.99 %) 250

Copper ( 5 % Zinc) 600

Aluminum (99.99 %) 175

Aluminum alloys 600

Low carbon steel 1000

Zinc 50

Tin 25

Lead 25

Table 8.1 Recrystallization temperatures for various metals and alloys.

Pure metals have low recrystallization temperatures as compared with alloys. Zinc, tin

and lead have recrystallization temperatures below room temperature. This means that

these metals cannot be cold worked at room temperature since they crystallize

spontaneously, reforming a strain free structure.



The greater the prior deformation, the lower the temperature for the start of

recrystallization.

Increasing the annealing time decreases the recrystallization temperature for the start of

recrystallization.

During recrystallization stage, there is a significant drop in tensile strength, hardness

and a large increase in the ductility of the material (See Figure 8.2).

Grain Growth:

In this stage the tensile strength and hardness continue to decrease but at a much less

rate than the recrystallization stage. The major change observed during this stage is the

growth of the grain boundaries and reaching the original grain size (See Figure 8.2).

Figure 8.2 Effect of annealing on tensile strength, hardness, ductility and grain size.



Figure 8.3 Structural changes occurring during the annealing of a steel casting (approx

0.35% carbon). The as-cast Widmanstatten structure is reheated to some temperature

above its upper critical and then allowed to cool in the furnace.

The benefits of annealing are:

Improved ducti lity

Removal of residual stresses that result from cold-working or machining

Improved machinability

Grain refinement

Normalizing:

The normalizing of steel is carried out by heating approximately 100 oF above the UCT

(Upper Critical Temperature) followed by cooling in air to room temperature. Normalizing

can be applied above the UCT for both hypoeutectoid and hypereutectoid steels. Figure

8.4 shows the normalizing temperatures.



Figure 8.4. Normalizing temperatures for hypoeutectoid and hypereutectoid steels.

The following is the list of the reasons for normalizing the steel:

To produce a harder and stronger steel than full annealing

To improve the machinability

To modify and refine the grain structure

To obtain a relatively good ducti lity without reducing the hardness and strength

Figures 8.5, 8.6, 8.7 and 8.8 show the effect of annealing and normalizing on the

ductility, tensile strength, hardness and yield point of steels.

As indicated in Figure 8.5, annealing and normalizing do not present a significant

difference on the ductility of low carbon steels. As the carbon content increases,

annealing maintains the % elongation around 20%. On the other hand, the ductility of

the normalized high carbon steels drop to 1 to 2 % level.

Figures 8.6 and 8.7 show that the tensile strength and the yield point of the normalized

steels are higher than the annealed steels. Normalizing and annealing do not show a

significant difference on the tensile strength and yield point of the low carbon steels.



However, normalized high carbon steels present much higher tensile strength and yield

point than those that are annealed.

Figure 8.5 Ductility of annealed and normalized steels.

Figure 8.6 Tensile strength of normalized and annealed steels.

As seen from Figure 8.8, low and medium carbon steels can maintain similar hardness

levels when normalized or annealed. However, when high carbon steels are normalized

they maintain higher levels of hardness than those that are annealed.



Figure 8.7 Yield point of annealed and normalized steels

Figure 8.8 Hardness of normalized and annealed steels.



Quenching & tempering:

Steels can be heat treated to high hardness and strength levels. The reasons for doing

this are obvious. Structural components subjected to high operating stress need the high

strength of a hardened structure. Similarly, tools such as dies, knives, cutting devices,

and forming devices need a hardened structure to resist wear and deformation.

As-quenched hardened steels are so brittle that even slight impacts may cause fracture.

Tempering is a heat treatment that reduces the brittleness of a steel without significant ly

lowering its hardness and strength. All hardened steels must be tempered before use.

QUENCH AND TEMPERING PROCESSES:

(1) Conventional Heat, Quench and Temper process

(2) Martempering

(3) Austempering

Conventional Heat, Quench and Temper Process:

In this process, Austenite is transformed to Martensite as a result of rapid quench from

furnace to room temperature. Then, martensite is heated to a temperature which gives

the desired hardness. One serious drawback is the possibility of distorting and cracking

the metal as a result of severe quenching required to form Martensite without

transforming any of the austenite to pearlite. During quenching process, the outer area

is cooled quicker than the center. Thinner parts are cooled faster than parts with greater

cross-sectional areas. What this means is that transformations of the Austenite are

proceeding at different rates. As the metal cools, it also contracts and its microstructure

occupies less volume. Extreme variations in size of metal parts complicate the work of

the heat treater and should be avoided in the designing of metal parts. This means there

is a limit to the overall size of parts that can be subjected to such thermal processing.

Figure 8.9 shows the conventional hardening, tempering process.



Figure 8.9 Conventional quenching and tempering process.

Martempering (Marquenching):

To overcome the restrictions of conventional quenching and temperi ng , Martempering

process can be used. Martempering or marquenching permits the transformation of

Austenite to Martensite to take place at the same time throughout the structure of the

metal part. This is shown in Figure 8.10. By using interrupted quench, the cooling is

stopped at a point above the martensite transformation region to allow sufficient time for

the center to cool to the same temperature as the surface. Then cooling is continued

through the martensite region, followed by the usual tempering.

Austempering:

This is the second method that can be used to overcome the restrictions of conventional

quench and tempering. The quench is interrupted at a higher temperature than for

Martempering to allow the metal at the center of the part to reach the same temperature

as the surface. By maintaining that temperature, both the center and the surface are

allowed to transform to Bainite and are then cooled to room temperature.



Figure 8.10 Martempering process.

Figure 8.11 Austempering process.



Advantages of Austempering:

(1) Less distortion and cracking than martempering,

(2) No need for final tempering (less time consuming and more energy efficient)

(3) Improvement of toughness (impact resistance is higher than the conventional quench

and tempering)

(4) Improved ducti lity

Limitations of Austempering:

Austempering can be applied to parts where the transformation to pearli te can be

avoided. This means that the section must be cooled fast enough to avoid the formation

of pearlite. Thin sections can be cooled faster than the bulky sections. Most industrial

applications of austempering have been limited to sections less than 1/2 in. thick. The

thickness can be increased by the use of alloy steels, but then the time for completion of

transformation to bainite may become excessive.

In Austempering process, the end product is 100% bainite. It is accomplished by first

heating the part to the proper austenitizing temperature followed by cooling rapidly in a

slat bath which is maintained between 400 and 800 oF. The part is left in the bath until

the transformation to bainite is complete. The steel is caused to go directly from

austenite to bainite.

Effects of Quenching medium on Hardness:

According to the functional requirements of the component, different engineering

components need different hardness for their long service life. Different quenching

media generate different final microstructures (like coarse pearlite, fine pearlite, bainite,

martensite etc.) and thus give different hardness values. So the type of quenching

media and the cooling rate both decide the final microstructure. To derive the suitable



hardness, material technologists must know the effect of the quenching medium and

cooling rate, on the hardness of steel. Knowledge of generating different hardness is of

great help in industries for the manufacture of components like gears, cams, shafts,

axles, pins etc. to increase their service life.

THEORY:

Quenching, which means drastic(rapid) cooling, always gives high hardness in ferrous

systems (metal involving iron) because of mechanism of allotropic transformation

suppression.

Mechanism of heat removal during quenching is grouped into three stages:

1) Vapour Blanket Stage: Here the quenching medium (Oil, Water or Brine)

vaporizes at the metal surface due to the high temperature and a thin fi lm of

vapour called vapour blanket, surrounds the hot metal. Presence of vapour

retards the heat transfer process and hence the rate of cooling is relatively low.

2) Vapour Transport Cooling Rate: Here metal has cooled a temperature where

vapour blanket is no longer stable. Because of absence of vapour between metal

and liquid, heat transfer rate increases and cooling rate is maximum.

3) Liquid Cooling Stage: Here the metal reaches the temperature of boiling point of

quenching medium. Heat given by the hot metal is utilized in boiling the liquid. In

this stage, cooling rate is lowest.

To avoid cracks, distortion and warp age, quenching medium should show high initial

cooling rate to avoid transformation in the nose region of the TTT curve, followed by

slow cooling rate through out the low temperature range.

Rise in temperature of quenching medium due to immersion of the component, should

be controlled by selecting the proper volume of quenching medium along with necessary

cooling arrangement so that heat transfer rate gets maintained the level desired.

Practical Contents:

1) Measure the initial hardness of the given specimen on Rockwell Hardness Tester.

2) Load these specimens in the furnace and heat them to the hardening

temperature for 20 to 30 minute.

3) Quench these specimens in oil, water and brine respectively.

4) Measure the hardness of each of them after cooling.



Questions

1) What is soaking time? State its importance.

2) What is the necessity of studying the effect of quenching media?

3) What should be the nature of quenching media to avoid cracks, distortion or warp

age of component being hardened?



PRACTICAL: 9

HARDENABLITY OF GIVEN MATERIAL WITH JOMINY HARDENBILITY TEST

DATE:

Aim: TO MEASURE HARDENABLITY OF GIVEN MATERIAL WITH JOMINY HARDENBILITY TEST

Objective:

To understand the concept of hardenability and its relevance to heat treatment

procedure to be adopted in practice.

Introduction:

Hardenability is the property that determines the depth and distribution of hardness

induced by quenching in a ferrous alloy. The Jominy test, together with the appropriate

data, is ideally suited for predicting the hardness at a particular location within a section

of any given size regardless of the steel from which the section is made. It establishes a

correlation between the cooling rate and corresponding distance from the quenched end

for each of the test bars. This relationship is the fundamental one and remains

substantially unaltered so long as the Jominy procedure is strictly adhered to. It is

possible through this correlation to predict hardness within any given shaped object

once the cooling rate is known at the location of interest. Such cooling rates within the

objects may be determined experimentally or may be obtained by reference to

appropriate published data if the size shape and heat treatment of the object correspond

to the condition under which data were obtained.

Practical contents:

1) Understand the theory and relevance of hardenability.

2) Heat the specimen to the austenitizing temperature and soak it at this

temperature for 30 minutes.

3) After soaking a test specimen is removed rapidly and placed on a quenching

fixture.

4) The water tap shall be opened as soon as the test piece is fixed in position and

the time of spraying shall be at least 10 minutes. After this time, the cooling of the

test specimen is removed rapidly and placed on a quenching fixture.



5) Two flats for measuring the hardness shall be ground on the surface 1800 apart

and parallel to the axis of the test piece, along its entire length. They should be

0.4 to 0.5 mm deep shall be ground with an abundant supply of coolant so as to

prevent any heating likely to modify the microstructure of the quenched test

piece.

6) Rockwell hardness measurements are made at an interval of 1.5 mm along the

longitudinal center line of the flat surface.

7) Record the observations as under

Specimen Material:

Hardness before test:

Temperature & Socking Time:

Sr. No Distance from the quenched end (mm) Hardness (HRC)

8) Plot the graph of Distance v/s Hardness

Questions

1) Draw the neat diagram of standard specimen and practical set up.

2) What is hardenability? What are the factors on which hardenability depends?

3) What kind of transformation is desirable to have a greater hardenability?

4) Differentiate between hardness and hardenability.

5) What is the grain structure of martensite?

6) How is hardenability curve useful?

7) Why it is necessary to cool the test specimen of Jominy hardenability test while

grinding two flat surfaces for measurement purpose?



PRACTICAL: 10

LIQUID PENETRATION TEST

DATE:

Aim: TO PERFORM LIQUID PENETRATION TEST FOR GIVEN SAMPLE

Objective:

To understand principle, procedure & capabilities of Liquid / Dye Penetrant Test

Introduction:

Dye penetrant test is essentially useful in detecting minute discontinuities such as

cracks, shrinkages and porosity that are open to the surface. Parts to be tested are

treated with a penetrant. Penetrant is usually light, oil-like liquids which is applied by

dipping, spraying or brushing or in some other convenient manner. The liquid penetrant

is drawn into cracks and other discontinuities by strong capillary action. After the

penetrant ahs had time to seep in, the portion remaining on the surface is removed by

wiping or washing. This leaves the penetrant in all surface -connected discontinuities.

The pest part is now treated with a dry powder or a suspension of powder in a liquid.

This powder or developer acts like a sponge drawing the penetrant from the defect and

enlarging the size of the area of penetrant indication.

Practical contents:

1) Prepare the surface to be investigated and make it free from dirt and grease.

2) Apply cleaner, allow some time so that surface gets dried.

3) Spray dye penetrant on the surface and allow some time (usually 3 to 5 min.

varies from 2 min to few days)

4) Wipe out excess penetrant. (This may be carried out by a light spray of cleaner

and wiping it out)

5) Apply developer and observer indications.

6) If needed the developer once again.

7) Observe the defect



Questions

1) What types of properties of the dye are required to perform the LPT accurately?

2) Why the developer is used in LPT?

3) List the limitation & capabilities of LPT.

4) Mention the IS No. for DPT.

5) Draw the neat sketch of sample & indications



PRACTICAL: 11

MAGNETIC PARTICLE TEST

Aim: TO STUDY OF MAGNETIC PARTICLE TEST

Objective:

To study principle. procedure & capabilities of Magnetic Particle Test.

Introduction:

The magnetic particle test is one of the most powerful surface and/or subsurface crack

detection method/s for Ferromagnetic Materials. The principle of the operation is that,

when a component under test is magnetized, discontinuities which lie in a direction

generally transverse to the direction of magnetic field will cause a leakage field to be

formed. If leakage field is strong enough, its presence and therefore the discontinuity is

detected by use of finely divided ferromagnetic particles applied over the surface. Some

of the ferromagnetic particles are influence by leakage field and form an outline of the

discontinuity called as an indication. The indication may give about size, shape and

location of the flaw.

Practical contents:

1) Determine the setting up procedure, parameters.

2) Clean the specimen thoroughly. Degreasing may be carried out by spirit or

trichloroethylene bath.

3) Setup the equipment for the nature of the defect to be detected (cracks, surface,

subsurface, porosity etc.). Based on it select the electrical current source.

4) Apply magnetic particles.

5) Perform the test in different orientations of magnetic field application and record

the nature and extent of indication with and without fluorescent powder.

6) Demagnetize the work piece and check for results.



Questions:

1) Briefly explain the principle and procedure of MPT with neat sketches.

2) Comment on applications, advantages and limitations of MPT.



DATE:

Aim: TO STUDY OF ULTRASONIC TEST

Objective:

To understand principle, procedure and capabilities of ultrasonic test.

Introduction:

The basic principle of the method is detecting the change in attenuation of sound energy

(ultrasonic) – the change being caused by a flaw or the material. In this test ultrasonic

sound waves (above the audible range) capable of penetrating and medium of

appreciable thickness at speeds of several thousand meter/sec, are used. The

frequency may range from 1 to 15 MHz.

There will be changes in probing medium when there is a flaw which will be detected

and indicated by the equipment – the ultrasonic flaw detector.

The pulse-echo technique is widely preferred. This employs a single probe (transducer)

as transmitter and receiver of ultrasonic waves. The ultrasonic waves with high

frequency are generated by piezoelectric effect. When these high frequency waves,

enter the material being tested, part of it is reflected and converted back to an electrical

impulse. This electrical impulse is amplified and rendered visible as an indicator or pip

on the screen of the oscilloscope. When the sound wave reaches the other side of the

other side of the material, it is reflected back and shows as another pip on the screen

further to the right of the first pip (pulse). If there is a flaw between the front and back

surfaces of the material (i.e. the thickness), it will show as a third pip (pulse) on the

screen between the two indications or pulses.

Since the indications on the oscilloscope screen measure the elapsed time between

reflection of the pulse from the front and back surfaces, the distance between indications

is a measure of thickness of the material. The location of a defect can therefore be

accurately determined from the location on the screen.

PRACTICAL: 12

ULTRASONIC TEST



Angle probes may be used to detect flaws which are not oriented perpendicular to the

direction of propagation of sound waves.

Practical Contents:

1) With the help of the manual of the equipment, get acquainted with the operating

details of ultrasonic flaw detector.

2) Calibrate the instrument using I.I.W.-V1 Block.

3) Scan the given samples and report the indications in following manner.

4) Sketch the samples you have scanned illustrating the flaws in it.

Sr. No CRT

Reading

Length of defect from probing

surface (mm)

Questions

1) Briefly explain the principle of Ultrasonic Testing. State various methods of

conducting UT and sketch the operating principle of the method you have used in

lab.

2) Evaluate UT with other with respect to other NDT methods you know.

3) Illustrate internal construction of following probes and mention the selection

criteria for each of them.

a) Normal Probe

b) Dual Crystal Probe

c) Angle Probe

4) Explain briefly following terminology in context of UT.

a) Attenuation

b) Dead Zone

c) Near Zone

d) Couplants

e) Acoustic impedance

f) Sensitivity

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