Numerical and Experimental Investigation of Austenite Transformation of Bearing Steel GCr15 in Non-isothermal and Isothermal Processes

The warm rolling and warm forging processes of bearing steel balls undergo plastic deformation in two-phase zone of bearing steel, and the research on austenite transformation of bearing steel in two-phase zone has important significance. This article utilizes incubation period in the austenite transformation process of bearing steel and uses genetic algorithm (GA) to solve the kinetic model of bearing steel austenite transformation in non-isothermal (continuous heating) process established based on JMAK (Johnson-Mehl-Avrami-Kolmogorov) method. The model is in good agreement with the results of thermal expansion experiments, verifying its effectiveness. In the isothermal (insulation) process after non-isothermal process, based on the basic theories of diffusion and phase transition kinetics, an evolution model of the volume fraction and particle size of undissolved carbides during the insulation process depending on the insulation temperature and time is established. A grain size evolution model considering the pinning effect of second-phase particles is also presented. Genetic algorithm is used to solve the models, which are in good agreement with the experimental results of the isothermal process, and the effectiveness of the models are verified. The research on austenite transformation of bearing steel during non-isothermal and subsequent isothermal process lays a solid foundation for the research on deformation and microstructure evolution of subsequent bearing steel in two-phase zone.