Chapter 12 – Steel Products • Key: carbon content: – Steel – alloy consisting mostly of iron with a little carbon (0.05% - 2.04% by weight) – Also have: • Iron = iron-carbon alloy with less than 0.005% carbon. • Cast iron = carbon content between 2.1% - 4.0% • Wrought iron – contains 1 – 3% by weight of slag in the form of particles elongated in one direction – more rust resistant than steel and welds better
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Chapter 12 – Steel Products Key: carbon content: –Steel – alloy consisting mostly of iron with a little carbon (0.05% - 2.04% by weight) –Also have: Iron.
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Chapter 12 – Steel Products
• Key: carbon content:– Steel – alloy consisting mostly of iron with a little
carbon (0.05% - 2.04% by weight)– Also have:
• Iron = iron-carbon alloy with less than 0.005% carbon.
• Cast iron = carbon content between 2.1% - 4.0%
• Wrought iron – contains 1 – 3% by weight of slag in the form of particles elongated in one direction – more rust resistant than steel and welds better
Brief History:• Iron age (12th century BC) (mostly wrought iron) – weapons made
with inefficient smelting methods. The best weapons? When iron combined with carbon!
• Became more common after more efficient production methods were devised in the 17th century.
• With invention of the Bessemer process in the mid-19th century, steel became relatively inexpensive, easily mass-produced and high quality.
• Blast Furnace then Bessemer Furnace
Low cost method for removing carbon and impurities
The “abc’s” of Steel Making:
• Raw Material:– Carbon in the form of coke
– Iron ore (Fe2O3)
– Limestone (CaCO3)
– Air (lots of it!!)
The “abc’s” of Steel Making:
• Coke– Solid residue product from the destructive
distillation of coal.– About 80 to 95% C.– Made by heating black coal in small ovens at
300 C for 24 hours in a coke plant.
The “abc’s” of Steel Making:
• The iron ore– Consists of oxides in nature of iron and
oxygen• Primarily magnetite (Fe3O4) or hematite (Fe2O3)
• The blast furnace basically separates the iron from the oxygen in a reduction process
– Mined primarily in Australia, Brazil and Canada.
The “abc’s” of Steel Making:
• The limestone– Acts as a flux – converts impurities in the ore
into a fuseable slag
The “abc’s” of Steel Making:
• Air– Preheated by fuel gas from the coke ovens to
about 1000 C.– Delivered to the blast furnace at 6,000 m3/min– Passes through furnace and burns the coke to
produce heat required and also generates the carbon monoxide.
The “abc’s” of Steel Making:
• Typical blast furnace:– 1.6 tons of iron ore– 0.18 tons of limestone– 0.6 tons of coke– 2 -3 tons of preheated air
The “abc’s” of Steel Making:
• Step 1 – The Blast Furnace:– Stands 300 feet tall– Designed to run continuously for 4 -5 years
before being relined.– Heat generated by burning coke in the
preheated air.– Coke acts as reducing agent and changes to
carbon monoxide (the reducing agent) which removes the oxygen from the iron oxide.
The “abc’s” of Steel Making:
• Step 1 – The Blast Furnace:– Two important chemical reactions:
• Oxidation of the carbon from coke:
COOC 22 2
• Reduction of iron ore:
233 323 COFeCOOFe
The “abc’s” of Steel Making:
• Step 1 – The Blast Furnace:– Four primary zones – the bottom zone (zone
4) reaches temperature of 1800 C – this is where iron is tapped off.
– The top zone (zone 1) – where coke is burned and moisture driven off.
– Zone 2 – slag coagulates and is removed.
The “abc’s” of Steel Making:
• Step 1 – The Blast Furnace:– Products from the blast furnace:
• Iron transported in steel shelled ladles• Pig iron (brittle w/ 4% carbon)
Step 2: Manufacturing of Steel from Iron
• Two common methods:– Bessemer Furnace = Ingots = molten steel
poured into molds to create ingots which then go through forging press and roughing mill to create billet, bloom or slab, OR:
– Continuous cast – continuous process to again create a billet, bloom, slab or “as cast semis”
• Step 2 – The Bessemer converter:– Used for REFINEMENT:
• Takes pig iron with high C content and removes C.• Removes impurities such as Si and Mn (via
oxides)
– Much smaller furnace (vs. Blast furnace)– Lowered cost of steel making– Poured into molds to form ingots
Replaced by basic oxygen process and electric arc furnace.
Steel Ingots (after step 2)
Figure 9-12: processing of refined steel into products.
F 9-13 – The whole spectrum of steel products!
Optional Step 2 (directly from blast furnace)
Step 2 w/ Continuous Casting• Overcomes the ingot related difficulties of:
– Piping and entrapped slag– More cost effective
• Process– molten metal continuously flows from the ladle
into a tundish– through a bottomless,water-cooled mold– temp controlled water spray not fully cooled– Straightened, reheated, sized, and cut-off– Advantages– Common for Structural Shapes
Continuous Casting
Steel Types (Brief Overview) Much more detail in Chapter 14
Cast Iron Types (remember carbon > 2%)
• Gray iron• Ductile iron• Austempered ductile iron• White iron• Malleable iron
• Much more will be said about cast irons later!
HRS vs. CRS
• HRS– AKA hot finishing – ingots
or continuous cast shapes rolled in the “HOT” condition to a smaller shape.
– Since hot, grains recrystallize without material getting harder!
– Dislocations are annihilated (recall dislocations impede slip motion).