1. Most people would rather die than think; in fact, they do so.
–Bertrand Russell

2. Martensite (MAR)
Very hard, very strong
due to:
solution hardening
by xs carbon
residual internal strain
But……

3. Martensite (MAR)
Toughness = ??

4. Hardenability
Definitions -
For steels:
harden = make MAR
hardenability = ability to make MAR

5. Hardenability
Problem:
Suppose want to full harden a shaft – i.e., make MAR all the way through shaft
center cools slowly
surface cools rapidly

6. Hardenability
So - this could happen:

7. Hardenability
Solution to problem: increase quench rate
But rapid quenching leads to distortion & cracking
Generally quench as gently as possible

8. Hardenability
So….is there a solution??
OK, how to do that?
What controls position of TTT curves?

9. Hardenability
So….is there a solution??
OK, how to do that?
What controls position of TTT curves?
a. % C – more C to move…slower P growth
b. add alloy elements…slows C diffusion
c. increase AUS grain size. P nucleates on AUS
grain boundaries. Increases diffusion distance

10. Hardenability

11. Hardenability

12. Hardenability
Shift curves to right: Mn Mo Cr V Nb Si Ni W

13. Review today's notes
a. what is martensite
b. why is martensite
c. martensite structure & properties
Read text: pp ;
Do problems in text: 9.55, 9.57, 10.14, 10.16
4. Do second set of problems on website