1. Chapter 14 – Carbon and Alloy Steels
All of these steels are alloys of Fe and C
Plain carbon steels (less than 2% carbon and negligible amounts of other residual elements)
Low Carbon (less than 0.3% carbon)
Med Carbon (0.3% to 0.6%)
High Carbon (0.6% to 0.95%)
Low Alloy Steel
High Alloy Steel
Stainless Steels (Corrosion-Resistant Steels) – contain at least 10.5% Chromium
Note, most steel alloys contain less than 1.0% carbon

2. AISI - SAE Classification System AISI XXXX
American Iron and Steel Institute (AISI)
classifies alloys by chemistry
4 digit number
1st number is the major alloying element
2nd number designates the subgroup alloying element OR the relative percent of primary alloying element.
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

3. Examples:
2350
2550
4140
1060

4. Common Carbon and Alloy Steels:

5. AISI - SAE Classification System
letter prefix to designate the process used to produce the steel
E = electric furnace
X = indicates permissible variations
If a letter is inserted between the 2nd and 3rd number
B = boron has been added
L = lead has been added
Letter suffix
H = when hardenability is a major requirement
Other designation organizations
ASTM and MIL
may contain a letter prefix to designate the process used to produce the steel
E = electric furnace
X = indicates permissible variations such as in range of material %
not a prefix, but inserted between the 2nd and 3rd number
B = boron has been added
L = lead has been added (12L14)
suffix
H = when hardenability is a major requirement
Other designation organizations
ASTM (American Society for Testing and Materials)
MIL (Military Specification)

6. AISI/SAE most common, also have Unified Numbering System (UNS) and ASTM

7. Should be considered first in most application 3 Classifications
Plain Carbon Steel
Plain Carbon Steel
Lowest cost
Should be considered first in most application
3 Classifications
Low Carbon (less than 0.3% carbon)
Med Carbon (0.3% to 0.6%)
High Carbon (0.6% to 0.95%)
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)

8. Plain Carbon Steel
Again, alloy of iron and carbon with carbon the major strengthening element via solid solution strengthening.
If carbon level high enough (greater than 0.6%) can be quench hardened (aka: dispersion hardening, through hardened, heat treated, austenized and quenched, etc..).
Can come in HRS and CRS options
The most common CRS are 1006 through 1050 and 1112, 1117 and other free machining steels
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)

9. Plain Carbon Steel Low Carbon (less than 0.3% carbon)
Low strength, good formability
If wear is a potential problem, can be carburized (diffusion hardening)
Most stampings made from these steels
AISI 1008, 1010, 1015, 1018, 1020, 1022, 1025
2. Med Carbon (0.3% to 0.6%)
Have moderate to high strength with fairly good ductility
Can be used in most machine elements
AISI 1030, 1040, 1050, 1060*
High Carbon (0.6% to 0.95%)
Have high strength, lower elongation
Can be quench hardened
Used in applications where surface subject to abrasion – tools, knives, chisels, ag implements.
AISI 1080, 1095
*Note, some texts including CES state med carbon as .3% to .5%

12. Carbon steels: low, med and hight
Trends?
Increasing carbon content – tensile strength increases, elongation decreases.

13. Plain Carbon Steel 1018 Low carbon Yield strength 55ksi 1045
Medium carbon Yield strength 70ksi
A36
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

14. 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.

15. 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)

18. Alloy Steel
Other elements (besides carbon) can be added to iron to improve mechanical property, manufacturing, or environmental property.
Example: sulfur, phosphorous, or lead can be added to improve machine ability.
Generally want to use for screw machine parts or parts with high production rates!
Examples: 11xx, 12xx and 12Lxx
Note,

19. Alloy Steel
Again, elements added to steel can dissolve in iron (solid solution strengthening):
Increase strength, hardenability, toughness, creep, high temp resistance.
Alloy steels grouped into low, med and high-alloy steels.
High-alloy steels would be the stainless steel groups.
Most alloy steels you’ll use fall under the category of low alloy.
Note,

20. Alloy Steel Most common alloy elements:
> 1.65%Mn, > 0.60% Si, or >0.60% Cu
Most common alloy elements:
Chromium, nickel, molybdenum, vanadium, tungsten, cobalt, boron, and copper.
Low alloy: Added in small percents (<5%)
increase strength and hardenability
High alloy: Added in large percents (>20%)
i.e. > 10.5% Cr = stainless steel where Cr improves corrosion resistance and 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

21. Alloying Elements used in Steel
Manganese (Mn)
combines with sulfur to prevent brittleness
>1%
increases hardenability
11% to 14%
increases hardness
good ductility
high strain hardening capacity
excellent wear resistance
Ideal for impact resisting tools
Manganese (Mn)
combines with sulfur to prevent brittleness
>1%
increases hardenability
11% to 14%
increases hardness
good ductility
high strain hardening capacity
excellent wear resistance
Ideal for impact resisting tools
Sulfur (S)
usually not desired in steel because it will impart brittleness, but okay if combined with Mn
Some free-machining steels contain 0.08 to 0.15% S

22. Alloying Elements used in Steel
Sulfur (S)
Imparts brittleness
Improves machineability
Okay if combined with Mn
Some free-machining steels contain 0.08% to 0.15% S
Examples of S alloys:
11xx – sulfurized (free-cutting)
Sulfur (S)
usually not desired in steel because it will impart brittleness,
but okay if combined with Mn
Some free-machining steels contain 0.08 to 0.15% S

23. Alloying Elements used in Steel
Nickel (Ni)
Provides strength, stability and toughness, Examples of Ni alloys:
30xx – Nickel (0.70%), chromium (0.70%)
31xx – Nickel (1.25%), chromium (0.60%)
32xx – Nickel (1.75%), chromium (1.00%)
33XX – Nickel (3.50%), chromium (1.50%)
Nickel (Ni)
added to steel to increase toughness and impact resistance
2% to 5%
typically used in combination with Chromium and Molybdenum
12% to 20% Nickel AND low amounts of Carbon
possess great corrosion resistance
Invar
contains 36% Ni
virtually no thermal expansion
used for sensitive measuring devices

24. Alloying Elements used in Steel
Chromium (Cr)
Usually < 2%
increase hardenability and strength
Offers corrosion resistance by forming stable oxide surface
typically used in combination with Ni and Mo
30XX – Nickel (0.70%), chromium (0.70%)
5xxx – chromium alloys
6xxx – chromium-vanadium alloys
41xxx – chromium-molybdenum alloys
Molybdenum (Mo)
Usually < 0.3%
Mo-carbides help increase creep resistance at elevated temps
typical application is hot working tools
Chromium (Cr)
Usually less than 2%
used primarily to increase hardenability and strength
typically used in combination with Ni and Mo
chromium carbides can enhance wear resistance
Molybdenum (Mo)
Usually less than 0.3%
used to increase hardenability and strength
Mo-carbides help increase creep resistance at elevated temps
typical application is hot working tools

25. Alloying Elements used in Steel
Vanadium (V)
Usually 0.03% to 0.25%
increase strength
without loss of ductility
Tungsten (W)
helps to form stable carbides
increases hot hardness
used in tool steels
Vanadium (V)
Usually 0.03% to 0.25%
Va-carbides help to increase strength without loss of ductility
elastic limit, yield point, and impact strength
Tungsten (W)
helps to form stable carbides
increases hot hardness
used in tool steels

26. Alloying Elements used in Steel
Copper (Cu)
0.10% to 0.50%
increase corrosion resistance
Reduced surface quality and hot-working ability
used in low carbon sheet steel and structural steels
Silicon (Si)
About 2%
increase strength without loss of ductility
enhances magnetic properties
Copper (Cu)
0.10% to 0.50%
helps to increase corrosion resistance
surface quality and hot-working ability decline
used in low carbon sheet steel and structural steels
Silicon (Si)
about 2%
helps to increase strength without loss of ductility
used in structural steels and spring steels
also helps to enhance magnetic properties

27. Alloying Elements used in Steel
Boron (B)
for low carbon steels, can drastically increase hardenability
improves machinablity and cold forming capacity
Aluminum (Al)
deoxidizer
0.95% to 1.30%
produce Al-nitrides during nitriding
Boron (B)
for low carbon steels, B can drastically increase hardenability
as the carbon content goes up the hardenabilty goes down
improves machinablity and cold forming capacity
Aluminum (Al)
deoxidizer
0.95% to 1.30%
produce Al-nitrides during nitriding

28. Corrosion Resistant Steel
Stainless Steels (Corrosion-Resistant Steels) – contain at least 10.5% Chromium
trade name
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.

29. Tool steel are generally used in a heat-treated state.
Refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools.
Characteristics include high hardness, resistance to abrasion (excellent wear), an ability to hold a cutting edge, resistance to deformation at elevated temperatures (red-hardness).
Tool steel are generally used in a heat-treated state.
High carbon content – very brittle
Wear Resistant, High Strength and Tough
High Carbon steels
Modified by alloy additions
AISI-SAE Classification
Letter & Number Identification

30. Tool Steel An A2 is an Air-Hardenable, Cold-worked material.
AISI-SAE tool steel grades[1]
Defining property
AISI-SAE grade
Significant characteristics
Water-hardening W
Cold-working O
Oil-hardening A
Air-hardening; medium alloy D
High carbon; high chromium
Shock resisting S
High speed T
Tungsten base M
Molybdenum base
Hot-working H
H1-H19: chromium base H20-H39: tungsten base H40-H59: molybdenum base
Plastic mold P
Special purpose L
Low alloy F
Carbon tungsten
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

31. Review CES!

33. Recall, tensile strength approximately 500 X BHN

34. A Quick Review of Heat Treating Processes from Chapter 13:
Note, LC = lower critical temperature which is temperature at which transition from ferrite to autstintie begins. At the upper critical temperature UC the transformation is complete! Note, Stay as close to UC as possible. MCSteel, UC = 1500 F.

35. Know These Basic HT Processes:
Full Annealing – Heat above the austenite temperature (or UC) until the composition is uniform. Cool very slowly (usually at room temperate outside the oven. Result: a soft, low-strength steel, free of significant internal stresses. Generally done before Cold Forming process.
Stress relief annealing – Heat slightly below austenitic temperature (or below LC) generally done following welding, machining or cold forming to reduce residual stress.
Process annealing: A process used to relieve stress in a cold-worked carbon steel with less than 0.3 wt% C. The steel is usually heated up to 550–650 °C for 1 hour, but sometimes temperatures as high as 700 °C. The image rightward shows the area where process annealing occurs.

36. Know These Basic HT Processes:
Normalizing: Similar to annealing but at higher temperature. Again, slow cooling. Result: uniform internal structure with somewhat higher strength than the annealing process. Machinability and toughness improved over the as-rolled condition.
Normalizing: Carbon steel is heated to approximately 55 °C above Ac3 or Acm for 1 hour; this assures the steel completely transforms to austenite. The steel is then air-cooled, which is a cooling rate of approximately 38 °C (68 °F) per minute. This results in a fine pearlitic structure, and a more-uniform structure. Normalized steel has a higher strength than annealed steel; it has a relatively high strength and ductility

37. Know These Basic HT Processes:
Through Hardening, Quenching and Tempering (and then slow cooling): – Heat above the austenite temperature (or UC) until the composition is uniform. Cool rapidly (Quench). Result: strong but brittle martensite structure. So temper and slow cool to improve toughness at the expense of strength.
The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, or impact resistance. Note that the electrical and thermal conductivity are slightly altered. As with most strengthening techniques for steel, Young's modulus is unaffected. Steel has a higher solid solubility for carbon in the austenite phase; therefore all heat treatments, except spheroidizing and process annealing, start by heating to an austenitic phase. The rate at which the steel is cooled through the eutectoid reaction affects the rate at which carbon diffuses out of austenite. Generally speaking, cooling swiftly will give a finer pearlite (until the martensite critical temperature is reached) and cooling slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.77 wt% C) steel results in a pearlitic structure with α-ferrite at the grain boundaries. If it is hypereutectoid (more than 0.77 wt% C) steel then the structure is full pearlite with small grains of cementite scattered throughout. The relative amounts of constituents are found using the lever rule.

38. Tensile Strength and Elongation vs Tempering Temperature

39. Know These Basic HT Processes:
Spheroidizing: (must have carbon content of 0.6% or higher) Spheroidite forms when carbon steel is heated to approximately 700 °C for over 30 hours. Spheroidite can form at lower temperatures but the time needed drastically increases, as this is a diffusion-controlled process. The result is a structure of rods or spheres of cementite within primary structure (ferrite or pearlite, depending on which side of the eutectoid you are on). The purpose is to soften higher carbon steels and allow more formability. This is the softest and most ductile form of steel. The image to the right shows where spheroidizing usually occurs.

40. HRS vs CRS vs Annealed?
HT?

41. Tensile Strength and Elongation for Various Alloy Steels

42. Properties of Some Structural Steels – All use ASTM call-outs
Examples of Structural Steels???