1. Chapter 12 – Steel Products
Key: carbon content:
Steel – alloy consisting mostly of iron with a little carbon (0.05% % 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
Iron – not usally used as an engineering material because of its low strength. Cast iron extremely hard to machine!

2. 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
The Bessemer process is a method of steel production named for British inventor Sir Henry Bessemer. During the Bessemer process, iron workers inject air into molten steel to remove carbon and impurities. After the Bessemer process was introduced in the 1850s, steel refining and production increased dramatically. Modern steel manufacturing uses a similar technique, but the process has been refined over the years to create high-quality steel with very few impurities.
Steel manufacturers use a special furnace, known as a Bessemer converter, to produce steel using this technique. They place iron in the furnace and melt it to produce a molten liquid, then use a high-powered blower to pass air through the liquified iron. As the air passes through, oxygen molecules within the air interact with minerals and carbon molecules in the metal. As the air exits the molten iron, it brings the carbon and other particles with it in the form of gas or slag. The remaining iron can then be poured into molds to form steel objects.
Using the Bessemer process, manufacturers were able to produce better quality steel than was previously possible. The resulting steel was stronger and more durable, allowing larger and longer-lasting structures to be built. This process also helped manufacturers produce steel more quickly, and at a lower cost than with previous techniques. For more than a century, the Bessemer process became the most popular method of mass steel production, and much of Bessemer's techniques live on in modern industry.
Low cost method for removing carbon and impurities

3. The “abc’s” of Steel Making:
Raw Material:
Carbon in the form of coke
Iron ore (Fe2O3)
Limestone (CaCO3)
Air (lots of it!!)

4. 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.

5. 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.

6. The “abc’s” of Steel Making:
The limestone
Acts as a flux – converts impurities in the ore into a fuseable slag

7. 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.

8. 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

9. The “abc’s” of Steel Making:
Step 1 – The Blast Furnace:
Stands 300 feet tall
Designed to run continuously for 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.

10. The “abc’s” of Steel Making:
Step 1 – The Blast Furnace:
Two important chemical reactions:
Oxidation of the carbon from coke:
Reduction of iron ore:

11. 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.

12. 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)

13. 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”
Solidification Concerns
The liquid steel is converted into finished shape called steel castings
Or the liquid steel is converted into suitable shapes for further processing
Ingots (to be machined to size, or remelted and cast)
Continuous casting (to make bar, slabs, billets)
Containment vessels are used in particular types of steel manufacture for pouring
Known as ladles (typically hold as much as 100 tons of molten steel)
Stirring, degassing, reheating, and various injection procedures are performed to increase the cleanliness of the steel
If you have ever seen the making of gravy during thanksgiving, the turkey drippings will separate (oil and broth). It can be difficult to keep the broth (bottom) and discard the oil (floating)
By extracting the metal from the bottom of the ladle, the slag and floating matter are not transferred
Solidification shrinkage
There is a large discontinuity at the melting point of the density of the steel in its liquid and solid states

14. 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
In the U.S., commercial steel production using this method stopped in It was replaced by processes such as the basic oxygen (Linz-Donawitz) process, which offered better control of final chemistry. The Bessemer process was so fast (10–20 minutes for a heat) that it allowed little time for chemical analysis or adjustment of the alloying elements in the steel. Bessemer converters did not remove phosphorus efficiently from the molten steel; as low-phosphorus ores became more expensive, conversion costs increased. The process permitted only limited amount of scrap steel to be charged, further increasing costs, especially when scrap was inexpensive. Use of electric arc furnace technology competed favourably with the Bessemer process resulting in its obsolescence
Replaced by basic oxygen process and electric arc furnace.

15. Steel Ingots (after step 2)

16. Figure 9-12: processing of refined steel into products.

17. F 9-13 – The whole spectrum of steel products!

18. 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 Casing
Overcomes the ingot related difficulties
pipe
entrapped slag
And structural variations along the length of the product.
Continuous Casting Process
molten metal continuously flows from the ladle into a tundish
Tundish is a second ladle that bottom feeds the molten metal.
through a bottomless water-cooled mold (usually made of copper)
temp controlled water spray  not fully cooled, but solid
Straightened, reheated, sized, and cut-off
ALL non-stop Makes Billets, slabs, bars
Advantages
Eliminates: piping, mold splatter, removing the ingot from the mold, further processing of ingots
Reduces:energy used, costs, Scrap, oxide inclusions
improves surfaces conditions, chemical composition

19. Continuous Casting
Steel is refined in the BOF or EAF and poured into a laddle. Laddle is transported to the caster facility and poured into the caster tundish. From the tundish, poured into a mold which determines final shape stays in the mold long enough to form a solid outer skin. The final caster is cut to length and usually undergoes another process for making the final shape. Note, this is a cast product so has flaws inherent to casitngs – read page 352

21. Steel Types (Brief Overview) Much more detail in Chapter 14

22. 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!
White Cast Iron … contains cementite.
Hard and brittle, hence their use is limited to wear resistant parts
Virtually unmachinable except for grinding
Applications: liners for ore crushing mills and some agricultural machinery parts
Gray Cast Iron … iron with graphite flakes
Excellent machineability, high thermal conductivity, vibration dampening properties, and good wear resistance
Applications: camshafts, small cylinder blocks, heavy duty brake drums, exhaust manifolds and clutch plates
Ductile iron – does not exhibit yuelding – greater % elongation and generally higher tensiles strength – crankshafts and heavily loaded gears

23. HRS vs. CRS HRS HRS Characterized by:
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).
HRS Characterized by:
Extremely ductile (i.e. % elongation 20 to 30%)
Moderate strength (Su approx 60 – 75 ksi for 1020)
Rough surface finish – black scale left on surface.

24. HRS vs. CRS CRS CRS Characterized by:
AKA cold finishing – coil of HRS rolled through a series of rolling mills AT ROOM TEMPERATURE.
Since rolled at room temperature, get crystal defects called dislocations which impede motion via slip!
AKA work hardening
Limit to how much you can work harden before too brittle.
How reverse? Can recrystallize by annealing.
CRS Characterized by:
Less ductlie – almost brittle (i.e. % elongation 5 to 10%)
High strength (Su approx 120 ksi for 1020)

26. AISI - SAE Classification System
American Iron and Steel Institute (AISI)
classifies alloys by chemistry
4 digit number
1st number is the major alloying agent
2nd number designates the subgroup alloying agent
last two numbers approximate amount of carbon (expresses in 0.01%)
American Iron and Steel Institute (AISI)
classifies alloys by chemistry
started by Society of Automotive Engineers (SAE)
provide standardization of steel used in the automotive industry
expanded by AISI to include all engineering materials
4 digit number
1st number is the major alloying agent
2nd number designates the subgroup alloying agent
last two numbers approximate amount of carbon
expresses in 0.01%
1080 steel would be plain carbon steel with 0.80% carbon
4340 steel would be Mo-Cr-Ni alloy with 0.40% carbon
Refer to table 6-2 in book

27. Plain Carbon Steel vs. Alloy Steel
Plain Carbon Steel (10xx)
Lowest cost
Should be considered first in most application
3 Classifications
Low Carbon Steel
Medium Carbon Steel
High Carbon Steel
Plain Carbon Steel
Lowest cost
Should be considered first in most application
3 Classifications
Low Carbon Steel
Less than 0.20% Carbon
Good formability and weldability
Lacks hardenability (Difficult to harden)
Medium Carbon Steel
0.20% to 0.50% Carbon
Good toughness and ductility
Poor Hardenability (typically limited to water quench)
High Carbon Steel
Greater than 0.50% carbon
Low formability
High hardness and wear resistance
Poor hardenability (quench cracking occurs)

28. Plain Carbon Steel (10xx)
1018
Low carbon Yield strength 55ksi
1045
Medium carbon Yield strength 70ksi
ASTM A36 or A37 – aka structural steel
Low carbon Yield strength 36ksi
12L14
Low carbon Yield strength 70ksi
1144
Medium carbon Yield strength 95ksi
Examples of some plain carbon steels (non alloys)
1018: low carbon (.18%)
easy to cold form, bend, braze, and weld
Maximum hardness Rockwell 72B
Yield strength is 55ksi
1045: medium carbon (.45%)
more difficult to machine than 1018
Maximum hardness Rockwell 90B
Yield strength is 70ksi
A36: low carbon (.26%) (cold rolled)
General purpose steel
Maximum hardness Rockwell 68B
Yield strength is 36ksi
12L1: low carbon (.26%) contains LEAD
Excellent machining (due to lead)
Ductile for bending, crimping, riveting.
Maximum hardness Rockwell 85B
1144: medium carbon (.44%)
Good heat treat capabilities
Maximum hardness Rockwell 97B
Yield strength is 95ksi

29. Plain Carbon Steel vs. Alloy Steel
> 1.65%Mn, > 0.60% Si, or >0.60% Cu
Most common alloy elements:
Chromium, nickel, molybdenum, vanadium, tungsten, cobalt, boron, and copper.
Added in small percents (<5%)
increase strength and hardenability
Added in large percents (>20%)
improve corrosion resistance or stability at high or low temps
Alloy Steel
What classifies a steel as an Alloy Steel
> 1.65%Mn, > 0.60% Si, or >0.60% Cu
Definite or minimum amount of an alloying element is specified
Most alloying elements added to steel are < 5%
to increase strength and hardenability
Most alloying elements added to steel are > 20%
to improve corrosion resistance or stability at high or low temps

30. Corrosion Resistant Steel
Stainless Steel
10.5% < Cr < 27% = stainless steel – used for corrosion resistance
AISI assigns a 3 digit number
200 and 300 … Austenitic Stainless Steel
400 … Ferritic or Martensitic Stainless Steel
500 … Martensitic Stainless Steel
Stainless Steel is corrosion resistant!!
trade name
due to chromium oxide on the surface of the metal
S.S. Series
200 and 300 … Austenitic
nonmagnetic
high formability
very high corrosion resistance
twice the cost of ferritic S.S.
400 … Ferritic or Martensitic
poor ductility and formability
lowest cost S.S.
500 … Martensitic
high strength
1.5 times the cost of ferritic S.S.

31. Wear Resistant, High Strength and Tough High Carbon steels
Tool Steel
Wear Resistant, High Strength and Tough
High Carbon steels
Modified by alloy additions
AISI-SAE Classification
Letter & Number Identification
Wear Resistant, High Strength and Tough
High Carbon steels
Modified by alloy additions
AISI-SAE Classification
Letter & Number Identification

32. Classification Tool Steel
Letters pertain to significant characteristic
W,O,A,D,S,T,M,H,P,L,F
E.g. A is Air-Hardening medium alloy
Numbers pertain to material type
1 thru 7
E.g. 2 is Cold-work
Classification
Letters pertain to significant characteristic
W,O,A,D,S,T,M,H,P,L,F
E.g. A is Air-Hardening medium alloy
Numbers pertain to material type
1 thru 7
E.g. 2 is Cold-work
An A2 is an Air-Hardenable, Cold-worked material.
Read book and look at table 6-6