Microstructure effects on improving rolling contact fatigue by a double-quenching heat treatment process for GCr15 steel

The heat treatment process is important in improving the rolling contact fatigue (RCF) life of GCr15 bearing steel by changing the microstructure. The conventional heat treatment process of GCr15 bearing only has one quenching (CQ) process, and the corresponding RCF life cannot satisfy the requirements of many applications. A double-quenching (DQ) heat treatment with two quenching processes was proposed, and it can improve the RCF life. However, the improving mechanisms are not clarified. Therefore, the authors applied the CQ and the DQ heat treatment processes on GCr15 bearing steel and performed the ball-on-disk RCF tests for the specimens heat treated by the different processes. Moreover, comparisons of the microstructure and mechanical behavior between specimens were made. The results show that the DQ heat treatment decreases the average grain size, enhances the retained austenite content, and has no special effect on the carbide distribution. It also increases the homogeneity of grains, hardness, and retained austenite distribution. Moreover, the combined effect of grain size and retained austenite evolutions is the main mechanism that decides the RCF life improvement.