Effect of multiple deep cryo-treating and tempering on microstructure and property evolution of high carbon bearing steel

Interest has been shown in cryogenic treatments over the last seven decades mainly due to the transformation of retained austenite and the precipitation of fine carbides. By changing the microstructure, cryogenic treatments can improve wear resistance and hardness to some extent. In this work, the effect of multiple deep cryo-treating and tempering (DCTT) on microstructural evolution in 52100 bearing steel has been investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The Rockwell hardness tests were also conducted to verify the microstructure evolution. Moreover, the dilatometry was used to estimate the dimensional stability. The results demonstrated that DCTT not only contributes to the precipitation of nano-size carbides, but also leads to a more homogeneous size distribution. It was also proved that the variation of carbides and hardness could be attributed to the synergy of decrease of retained austenite and movement of carbon atoms brought in DCTT. Furthermore, the sample subjected to DCTT exhibits the highest wear resistance property.