Driving martensitic transformation through pre-cold deformation: Unveiling the mechanism of microstructural evolution in martensite bearing steel

Abstract

Bearing steel is used to produce bearing components through preforming processes, such as cold heading and cold rolling, prior to heat treatment. Cold rolling is a key developmental direction for manufacturing high-performance bearing. This research comprehensively examines how pre-cold deformation affects the microstructural evolution and mechanical characteristics of martensitic bearing steel. The findings suggest that pre-cold deformation reduces the original austenite grain size decreases by half, and the cementite particles become more uniformly distributed. Simultaneously, pre-cold deformation treatment considerably increases the bearing steel hardness from 715HV to 768HV whilst maintaining its toughness. The homogenisation of cementite size and the increase in hardness enhance the wear resistance of the samples by 34%. Furthermore, we explores the microstructural evolution mechanisms during subsequent phase transformations: the bearing steel in the process of martensitic transformation, the pre-cold deformation treatment leads to a strong variant selection, which increases the intrinsic nucleation rate and reduces the autocatalytic nucleation rate of martensite. The change of nucleation positions causes the great differences in the crystallography of the samples. The martensite twins transforming into twinned variants that adhere to the Kurdjumov-Sachs orientation relationship. In this study, we have established a relationship linking crystallography, phase transitions, and mechanical properties.