Isothermal heat treatment of a bearing steel for improved mechanical properties

• The experimental steel is a new bearing steel developed in China.
• The optimal isothermal temperature is lower than martensite start temperature.
• Steel heat-treated with the optimum process has excellent mechanical properties.

This study aims to determine the optimum parameters of isothermal heat treatment process for a new bearing steel through orthogonal experiment method, and obtain improved mechanical properties of interest. Following the orthogonal experiment, a verification experiment with isothermal temperature lower than martensite start temperature was conducted, and microstructure evolution in isothermal process was investigated. The steel, produced by austenitizing at 880 °C for 0.5 h and isothermal holding at 200 °C for 6 h, has excellent combination of mechanical properties, at the same time has fine and uniform microstructure. Under the optimum heat treatment condition, the impact strength and the hardness value increase by 28.8% and 5.2% respectively, while the tensile strength only decreases by 3.7%, compared with those of the conventional process.