High Quality Hardening Requires High Quenching Rates


The best toughness is achieved when the steel is martensitically hardened (high quench rate;
cooling curve 1)

 If the cooling rate required for martensitic transformation cannot be achieved, the steel undergoes
bainitic transformation. The achievable toughness is lower (cooling curve 3).

 At very slow cooling, the steel transforms into the pearlitic state: (cooling curve 4) very low

Resource: Kind&Co