Microstructural evolution and wear resistance of modified bearing steel with high carbon and chromium during quenching and tempering

The mechanical properties of bearing steel are closely related to alloy elements and heat treatment process parameters, with the determination of the latter relying on the microstructural evolution during heat treatment. Therefore, in this study, modified high carbon chromium bearing steel with increased Si and Mn content based on GCr15 was selected as the experimental material. With spheroidal pearlite as a starting point of microstructure for experimental research, multiple methods, including high-temperature laser confocal scanning microscope, scanning electron microscope, electron probe microanalyzer, carbide extraction combined with XRD, and wear resistance tests, were employed to investigate the microstructural evolution during quenching and tempering processes of modified high carbon chromium bearing steel and its effect on wear resistance. The results show that two nucleation modes of bearing steel during austenitization bring two types of austenite: pearlite-austenite and carbide-austenite. Through austenitization, carbides dissolve gradually, but some remain as undissolved carbides (GB-Cem) eventually at austenite grain boundaries. Throughout tempering, retained austenite gradually transforms into martensite and carbides during the holding stage. The precipitation of carbides increases progressively, accompanied by their coalescence and growth. Concurrently, the dislocation density in the matrix and around the carbides decreases, while the grain size enlarges, and grain orientation becomes more uniform. In the cooling stage, more uniform and slightly larger carbide particles are formed. Under the process of quenching at 880°C for 40 min, followed by tempering at 220°C for 180 min, the wear resistance of this bearing steel reaches its optimum level.