1. Hypoeutectoid steels - strength vs P content
The Fe-C system

2. Martensite (MAR)
Quenching suppresses diffusion
AUS ––> P rxn doesn't go!
But something has to happen -
a. too much carbon for FE
b. AUS needs to change structure
AUS ––> MAR
(very fine structure)

3. Martensite (MAR)
MAR is metastable……
C is trapped in wrong structure
MAR comes from AUS
AUS wants to exsolve C
& change atom arrangement

4. Transformation to MAR is time independent ….but temperature dependent
Martensite (MAR)
Transformation to MAR is time independent
….but temperature dependent
martensite start
martensite finish

5. Martensite (MAR)
TTT curves & MAR formation

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

7. Martensite (MAR)
Toughness = ??

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