Effect of initial spheroidizing microstructure after quenching and tempering on wear and contact fatigue properties of GCr15 bearing steel

GCr15 bearing steel with different initial spheroidizing microstructures was obtained by four different hot rolling and spheroidizing annealing processes. The effects of the initial spheroidizing microstructures on the microstructure and mechanical properties of the quenched and tempered steel were studied in detail. The microstructure of GCr15 bearing steel after quenching and tempering consisted of tempered martensite, M3C undissolved carbide and retained austenite. The spheroidization degree of carbides after spheroidizing annealing has a decisive influence on the size and distribution of undissolved carbides in quenching and tempering microstructure. During quenching and reheating, it is difficult to eliminate large network carbides, granular carbides and rod-shaped carbides. In contrast, with the increase of spheroidization degree and the decrease of cementite particle size in the initial microstructure, the particle size of undissolved carbide decreases. After quenching and tempering, the hardness of the on-line low-temperature spheroidizing annealing and new off-line isothermal spheroidizing annealing samples was 756 HV and 818 HV, respectively. The on-line low-temperature spheroidizing annealing process can not only reduce the time required for spheroidizing annealing process, but also improve the wear resistance and contact fatigue properties of quenched and tempered samples. Compared with the traditional off-line isothermal spheroidizing annealing, the wear rate of the on-line low-temperature spheroidizing annealing and off-line isothermal spheroidizing annealing were reduced by 26.5% and 46.1%, respectively. The rated life L10 of contact fatigue increased by 15.4% and 53.7%, and the median life L50 increased by 16.0% and 53.1%, respectively. At the same time, the change of the fraction of retained austenite after the contact fatigue test was reduced.