2011 Steelmaking Ch12

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Science of Materials

MTK 3A11

SteelmakingFabrication & Steel ProductsBudinski Chapter 12

Study Unit 1

Dr JJ Pretorius

Feb 2011


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MTK 3A 11 Steel Making Budinski Ch9 2

Study division goals

The aim of this study division is to develop

Insight into South Africa's role in global metal

production An understanding of how steels are made

A knowledge of the steel products that are

commercially available An understanding of steel terminology and steelspecification procedures


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Study unit goals

Having completed study unit 1 you should beable to

Describe the process of fabricating steel and theworkings of a typical steel mill

Discuss the processes involved in steel refining

List the steel products that are commerciallyavailable

Define certain steel terminology and specifications


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SA mineral production

SA has the world largest turnover resources of platinum-group- metals(87,7 % of world total), manganese (80 %), chromium (72,4 %), gold(40 %) and alumina-silicates.

SA accounts for over 40 % of the global production of :

ferrochromium,

PGMs

vanadium

SA is the worlds leading producer of chrome ore, gold, vermiculite and

alumino-silicates, and among the top three producers of manganeseore, titanium minerals and fluorspar.


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Chromium

- Corrosion and oxidationresistance

- Mild hardenability agent

- Improves wear resistance

- Promotes the retention of useful

strength levels at elevatedtemperatures

-Chromium is an irreplaceableconstituent in all stainless steels


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Manganese

- Desulfuriser and deoxidiser

- Most prevalent alloying agent in steels, after

carbon

- Flat rolled carbon and HSLA steels containup to 2% Mn for microstructural refinement

- Manganese may be substituted for part of

the nickel content in austenitic SS

- Tool and die steels rely on manganese for

deep hardening

- Farm equipment Plough


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Vanadium

Approximately 80% ofvanadium produced isused as ferrovanadiumor as a steel additive- specialty stainlesssteel, e.g. for use insurgical instruments andtools- rust resistant and high

speed tool steels- mixed with aluminium intitanium alloys used in jetengines and high-speedairframes


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Fluorspar (Fluorite)

fluorspar Metallurgical grade- flux to lower melting point ofraw materials in steel

production- aid the removal of impurities- aluminium production

Ceramic grade fluorite- manufacture of opalescent

glass, enamels and cookingutensils.

Acid grade fluorite- hydrofluoric acid bydecomposing the fluorite withsulphuric acid.


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Vermiculite

High-temperature insulationRefractory insulationFireproofing


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SOUTH AFRICAS MINERAL PRODUCTION

AND SALES



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SA mineral production

Witwatersrand Basin - 98 % of South Africas gold output ( as well asuranium, silver, pyrite)

Bushveld Complex PGMs; copper, nickel and cobalt mineralisation;

chromium and vanadium bearing titanium iron ore formations Transvaal Supergroup - manganese and iron ore

Karoo Basin (extending through Mpumalanga, KwaZulu-Natal, FreeState and Limpopo) - bituminous coal and anthracite resources

Phalaborwa Complex - copper, phosphate, titanium, vermiculite,

feldspar and zirconium ores Kimberlite pipes - diamonds

Northern Cape - lead-zinc ores associated with copper and silver

Heavy mineral sands - ilmenite, rutile and zircon;


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Pyrite Fools gold

Pyrite is usedcommercially for theproduction of sulfurdioxide, for use in

such applications asthe paper industry,and in themanufacture ofsulphuric acid, though

such applications aredeclining inimportance. It is alsoused for costume

jewellery.


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Bushveld Igneous Complex

The Bushveld Igneous Complex (or BIC) is a large igneousintrusion within the Earth's crust which has been tilted anderoded and now outcrops around what appears to be the edge

of a great geological basin. Located in South Africa, the BICcontains some of the richest ore deposits on Earth

The BIC extends over 66 000 km2

The largest known deposit of platinum group metals (PGMs)

platinum, palladium, rhodium, ruthenium, osmium and iridiumare recovered, as well as small amounts of gold, nickel, copperand cobalt.

Largest resources of chromium and vanadium in the world


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Bushveld Igneous Complex

Layering in theMain Zone, easternBushveld Complex.


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Steelmaking

Video clipSteelmaking Introduction


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Steelmaking


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Sishen iron ore mine


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Hematite (Fe2O3)


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Steelmaking

Video clipIron making


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Iron ore


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Blast furnace


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Steelmaking

Video clipBlast furnace


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Blast furnace diagram

1. Hot blast

2. Melting zone (bosh)

3. Reduction zone of ferrousoxide (barrel)

4. Reduction zone of ferric

oxide (stack)5. Pre-heating zone (throat)

6. Feed of ore, limestone,and coke

7. Exhaust gases

8. Column of ore, coke and

limestone9. Removal of slag

10.Tapping of molten pigiron

11.Collection of waste gases


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Blast furnace process

Coke Volatile constituents of coal are driven offby baking in an airless oven at 2000 C

Charge iron-bearing materials, coke, and flux

The charge is introduced into the furnace at thetop

Blasts of heated air are injected into the furnacethrough openings at the bottom of the shaft


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Blast furnace process

As the hot air encounters the coke, the coke is burnedalong with the injected fuels, producing the necessary heatand reducing gas to remove oxygen from the ore in the

reduction process Carbon in the gas combines with oxygen in the ore

As the iron melts, it descends and accumulates in thecrucible

Molten pig iron (5%C) and slag are drained from thecrucible through different tapping holes

The gas that exits from the top of the furnace goes througha cleaning process


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Direct reduction process


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Iron ore, coal and oxygen are reacted in a singlemelting vessel steel

Steel an alloy of iron and a restricted amount ofcarbon

C < 0.005% is considered pure iron

C > 0.06% lower limit commercial steel

C > 2.00% cast iron

More C brittle


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Fig 9-1


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Steel refining

Turning pig iron into steel

Basic oxygen furnace (BOF)

Electric arc furnace (EAF)Integrated steel mill

At least one blast furnace

A coke plant Various steel-refining processes

A number of product lines


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Basic oxygen furnace (BOF)


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Basic oxygen steelmaking


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Basic oxygen steelmaking

The oxygen steelmaking process converts the molten ironfrom the blast furnace - with up to 30% steel scrap - intorefined steel

High purity oxygen lance is brought in/blown in

lower carbon, silicon, manganese, and phosphorouscontent of the iron, while various fluxes are used to reducethe sulphur and phosphorous levels.

The impurities and a small amount of oxidized iron arecarried off in the molten slag that floats on the surface ofthe hot metal


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Electric arc furnace (EAF)


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Electric arc furnace (EAF)

Used to reduce iron from iron ore

Heat is generated from an electric arc between the meltand electrodes (graphite)

Oxygen is blown into the furnace, and lime and othermaterials are added to combine with the impurities andform slag

Molten iron is extracted and poured out via a tapping spout

Can then be processed again in an electric arc furnace tomake steel (special quality steel)


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Secondary Steelmaking

Speciality steels alter chemical composition

reduce non-metallic inclusions

Vacuum degassing

Ladle stirring injection

Ladle furnace heating


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Special refining processes

VAR Super alloysVIM Specialty Alloys

EBR To purify specialty alloys

ESR Tool steel and special purpose steels



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Steelmaking

Video clipBOS


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Concast


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Continuous casting (concast)

Refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section

Molten metal is poured through a graphite mould/cast

Cooled

The withdrawing rollers draw the solidified rod from themould at a continuous rate and pass it through additional

cooling and finally cross cutting

Improved mechanical properties of parts produced

Lower cost of operation for larger runs


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Concast


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Stand casting process and shapesproduced

Fig 9-10


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Steelmaking

Video clipConCast


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Processing of refined steel intoproducts

Fig 9-12


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MTK 3A 11 Steel Making Budinski Ch950

Converting steel into shapes


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Standard shapes

C-Shape

L-Shape

T-ShapeRail

Square & rectangulartubing

S-ShapeW-Shape


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Steelmaking

Video clipHot Rolling


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Steelmaking

Video clipCold Rolling


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Hot and cold finishing


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On your own

Steel terminology

Familiarise yourself with the terms used todescribe mill processing operations

Steel specifications

Regardless of the identification system used,

essential items need to be addressed inpurchasing a steel. Discuss these characteristics


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Next: Failure Analysis

Fracture mechanics

2011 Steelmaking Ch12

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