Patent ID: 7905967

Claim:
A method for manufacturing a martensitic stainless steel comprising the steps of: hot working a steel composition; cooling the hot-worked steel to a temperature lower than the Ms point to form a martensitic steel; carrying out preliminary softening heat treatment to the resulting martensitic steel; heating the resulting steel to a temperature equal to or above the Ac 1 point of the steel; quenching by cooling the steel from the temperature equal to or above the Ac 1 point of the steel; and, tempering the resulting quenched steel, said preliminary softening heat treatment is carried out under such conditions that the softening parameter P defined below is at least 15,400 and the softening temperature T is lower than the Ac 1 point: P (softening parameter): P=T (20+log t ) T: softening temperature [K] t: duration of softening treatment [Hr], wherein the martensitic stainless steel has a steel composition consisting essentially of, in mass percent, C: 0.15-0.22%, Si: 0.05-1.0%, Mn: 0.10-1.0%, Cr: 10.5-14.0%, P: at most 0.020%, S: at most 0.010%, Al: at most 0.10%, Mo: 0-2.0%, V: at most 0.50%, Nb: 0-0.020%, Ca: 0-0.0050%, N: at most 0.1000%, and a remainder of Fe and impurities and the steel composition is such that 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], and N*=N−[14{(V/51)+(Nb/93)}/10]−[14{(Ti/48)+(B/11)+(Al/27)}/10].