Patent attributes
The occurrence of delayed fracture which is found in a hot worked martensitic stainless steel is prevented by subjecting the steel, after hot working and prior to heat treatment for hardening by quenching from a temperature of at least Ac1 point of the steel, to preliminary softening heat treatment under such conditions that the softening parameter P defined below is at least 15,400 and the softening temperature T is lower than the Ac1 point:P(softening parameter):P=T(20+log t)T: softening temperature [K]t: duration of softening treatment [Hr].The present invention is particularly effective for a martensitic stainless steel having a steel composition in which the amount of effective dissolved C and N (=[C*+10N*]) where C* and N* are calculated by the following formulas is larger than 0.45:C*=C−[12{(Cr/52)×(6/23)}/10, andN*=N−[14{(V/51)+(Nb/93)}/10]−[14{(Ti/48)+(B/11)+(Al/27)}/10].
