Numerical Prediction and Experimental Validation of the Microstructure of Bearing Steel Ball Formation in Warm Skew Rolling

Direct deformation spheroidization (DDS) of carbides in warm conditions can improve the microstructure and performance of bearing steel. In this study, based on the carbide spheroidization mechanism, a set of multiaxial constitutive equations was developed to predict the microstructure evolution of bearing steel 52100 during warm skew rolling (SR). The derived multiaxial constitutive equations were implemented in DEFORM-3D software through a user subroutine. FE simulation of warm SR was performed to predict the formation and microstructure evolution of bearing steel balls (BSBs). The distribution of the normalized dislocation density, carbide phase transformation fraction and carbide spheroidization fraction within BSBs was predicted via FE simulation of warm SR. To validate the FE simulation results, warm SR experiments were conducted to produce BSB specimens with 30 mm diameter. The microstructure of BSB specimens was observed to analyze their microstructure distribution in the longitudinal and transversal sections. The predicted and experimental results were compared, and the results show that the predicted carbide spheroidization distribution agrees well with the experimental results. This indicates that the formation and microstructure of BSB during warm SR can be predicted well using the derived multiaxial constitutive equations.