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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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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Direct reduction process
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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Direct reduction process
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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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