Patent ID: 10287645

Abstract:
A steel has a chemical composition consisting of, by mass percent, C: 0.15-0.65%, Si: 0.05-0.5%, Mn: 0.1-1.5%, Cr: 0.2-1.5%, Mo: 0.1-2.5%, Ti: 0.005-0.50%, Al: 0.001-0.50%, and optionally at least one element selected from Nb: ≤0.4%, V: ≤0.5%, and B: ≤0.01%, Ca: ≤0.005%, Mg: ≤0.005%, and REM: ≤0.005%, and the balance of Fe and impurities, wherein Ni, P, S, N and O as impurities are Ni: ≤0.1%, P: ≤0.04%, S: ≤0.01%, N: ≤0.01%, and O: ≤0.01%. The steel is hot-worked into a shape and then sequentially subjected to heating the steel to a temperature exceeding the Ac1 transformation point and lower than the Ac3 transformation point and cooling. Then, a step of reheating the steel to a temperature not lower than the Ac3 transformation point and quenching the steel by rapid cooling, and a step of tempering the steel at a temperature not higher than the Ac1 transformation point are performed.