Quench Hardening (cont).
Critical cooling rate achieved when quench rate is just sufficient to prevent transformation to ferrite and pearlite
A range of quenching media can be used:-
- in order of severity 5% caustic soda, 5-10% brine, cold water, warm water, mineral oil, animal oil, vegetable oil
- Quenching into oils may produce bainite rather than martensite
Steels with less than 0.25%C cannot be hardened by quenching as the nose of the TTT curve is too close to the temperature axis