METHOD OF HEAT-TREATING STEEL, PROCESS FOR PRODUCING MACHINE PART, AND MACHINE PART

摘要

A method of heat treatment for steel containing at least 3.75 mass % of chromium, that allows the steel to have a surface layer portion nitrided to have high hardness and can also reduce/prevent grain boundary precipitates, includes the steps of: quench-hardening a steel to quench the steel, the steel containing 0.77 mass % to 0.85 mass % of carbon, 0.01 mass % to 0.25 mass % of silicon, 0.01 mass % to 0.35 mass % of manganese, 0.01 mass % to 0.15 mass % of nickel, 3.75 mass % to 4.25 mass % of chromium, 4 mass % to 4.5 mass % of molybdenum and 0.9 mass % to 1.1 mass % of vanadium with a remainder consisting of iron and impurity; plasma-nitriding the quench-hardened steel; and maintaining the plasma-nitrided steel at at least 300°C and not more than 480°C for diffusion.