To make the stainless steel 201-2 - high temperature phase in the austenite during cooling process to low temperature metastable phase - martensite, cooling rate must be greater than stainless steel 201-2 critical cooling rate.
Stainless steel 201-2 in the process of cooling, the cooling speed of surface and the core - definite difference, if the difference is large enough, may cause part is greater than the critical cooling rate into martensite, and less than the critical cooling rate of the core can not transform into martensite.
In order to ensure the whole cross section are transformed into martensite need to choose cooling capacity of quenching medium, to ensure that the stainless steel 201-2 core has a high enough cooling speed. But the cooling speed, stainless steel, 201-2 internal caused by uneven heat bilges cold shrink stress, may make the stainless steel 201-2 deformation or cracking. So, want to consider these two contradictory factors selecting quenching medium and cooling way.