1. Last class -
Improving hardenability - shift TTT curves to right
Tempering for toughness
stress relief
carbide and FE formation
Today -
Austenitization & tempering
Types of steels & irons

2. But first - a little more on the MAR transformationms mf T
MAR formation starts here
50% MAR - 50% AUS
MAR formation finishes here
Only changing temperature gives more MAR
Time at temperature doesn't help

3. Austenitizing
Hypoeutectoid steels: about 25°C above a3
no FE

4. Austenitizing
Hypereutectoid steels: betwn a3 & acm
undissolved carbides present - not
particularly detrimental

5. Tempering temperature/time
Depend upon desired props, application
Low T gives high hardness,
low toughness - wear
resistance
Hi T gives high toughness,
reduced hardness

6. Plain carbon steels alloy steels Low carbon steels high carbon steels
Types of steels
Plain carbon steels alloy steels
Low carbon steels high carbon steels
Stainless steels
Cr-0.15C ksi(ht treated)
440A Cr-0.5Ni-0.7C ksi(ht treated)
440C Cr-0.5Ni-1.2C ksi(ht treated)
Cr-0.5Ni-0.08C 60ksi(annealed)
Cr-0.5Ni-0.12C 65ksi(annealed)
Cr-10Ni-0.08C 85ksi(annealed)
304L Cr-10Ni-0.03C 80ksi(annealed)
Cr-12Ni-0.08C 85ksi(annealed)
Cr-0.15C cutlery
440A Cr-0.5Ni-0.7C cutlery
440C Cr-0.5Ni-1.2C ball bearings
Cr-0.5Ni-0.08C machine parts
Cr-0.5Ni-0.12C acid tanks
Cr-10Ni-0.08C food equipment
304L Cr-10Ni-0.03C food equipment
Cr-12Ni-0.08C chemical tanks
420
440A
440C
405
430
304
304L
316
Cr-0.15C
440A Cr-0.5Ni-0.7C
440C Cr-0.5Ni-1.2C
Cr-0.5Ni-0.08C
Cr-0.5Ni-0.12C
Cr-10Ni-0.08C
304L Cr-10Ni-0.03C
Cr-12Ni-0.08C

7. Types of steels
Stainless steels

8. Stainless steels 420 13Cr-0.15C 230ksi(ht treated)
440A Cr-0.5Ni-0.7C ksi(ht treated)
440C Cr-0.5Ni-1.2C ksi(ht treated)
Cr-0.5Ni-0.08C 60ksi(annealed)
Cr-0.5Ni-0.12C 65ksi(annealed)
Cr-10Ni-0.08C 85ksi(annealed)
304L Cr-10Ni-0.03C 80ksi(annealed)
Cr-12Ni-0.08C 85ksi(annealed)

9. Stainless steels
hardenable!
not hardenable!

10. austenitic SSs ----- ≥ 18% Cr & ≥ 8% Ni not hardenable
Stainless steels
sufficient amt of Ni
––> AUS at rm temp
austenitic SSs ≥ 18% Cr & ≥ 8% Ni
not hardenable

11. Types of steels
Plain carbon steels alloy steels
Low carbon steels high carbon steels
Stainless steels
Tool steels

12. Some types of tool steels
W1, W water hardening C
S2, S shock resisting 0.5C-Cr, W, Mo
O1, O oil hardening C-Mn, Ni, W
A2, A air hardening C-5Cr, V, Mo
H10, H hot work C-0.4V-3-5Cr
T1, T high-speed C-4Cr-18W-1-2V
Compositions not exact - higher grades have different compositions

13. Speaking of tools…..
What about "carbide" tools?
Most are WC fragments imbedded in Co matrix
angular WC fragments
Co matrix phase -
the "glue"

14. Speaking of tools…..
OK, then, what about "ceramic" tools?
Most from Al2O3 - pressed to near-net shape & sintered at ° C - ground on diamond wheels
At high temps, high hardness, wear resistance
Can use for mat'ls w/ up to RC66
Very brittle
Cost ≈ 2X that of carbide tools

15. Cast irons
Types
White - C is all in CM
Grey - C as graphite flakes
Ductile (nodular) - C as graphite nodules

16. Cast irons

17. Cast irons
White - C is all in CM
very brittle, wear resistant,
not machinable, limited use
Grey - C as graphite ("corn") flakes
Si added to graphitize,
brittle cuz of flake stress
raisers - cheap, widely
used, vibration damping
Ductile (nodular) - C as graphite
nodules "inoculated" w/
Mg or Ce to get nodules
- up to 40% EL

18. Case hardening
Gear tooth
Carburizing - pack & gas - add C from CO gas