The Impact of Deformation Conditions on Divorced Eutectoid Transformation in Bearing Steels

Abstract

The impact of deformation conditions on divorced eutectoid transformation (DET) is elucidated in bearing steels. The deformation experiments suggest that the effect of deformation on DET is two‐fold. In the case of large deformation reduction, the size of carbide particles is decreased, while the number density of deformation‐induced carbides is increased with increased deformation. When the deformation reduction is less than 30%, the degree of spheroidization is increased with increase of deformation reduction. Network carbides formed by M7C3‐type deformation‐induced carbides is obtained along prior austenite grain boundaries when deformation reduction is increased to 40%. Although the nature of deformation‐induced carbides is different from the carbides (M3C) formed by DET, the nature of spheroidized carbides after annealing continues to be M3C. With the increase of deformation passes, the number density of deformation‐induced carbides is increased. As regards the effect of deformation rate on DET, the degree of spheroidization decreases with the increase of deformation rate. The optimum condition is single‐pass deformation at 1073 K with a reduction of ≈30%. In this condition, only ≈0.5 h isothermal treatment at 993 K is adequate to complete the spheroidizing process, and the mean particle size after deformation is ≈0.2 µm.