Influence of microstructure on retained austenite and residual stress changes under rolling contact fatigue in mixed lubrication conditions

Abstract

The objective of this study was to understand how the near-surface microstructures of bearings are able to resist surface-initiated damage under rolling contact and mixed lubrication conditions. In the study, rolling elements were subjected to case-carburizing treatments to generate different microstructures containing from 20% to 30% retained austenite. The rolling elements, which developed either fine or coarse martensitic microstructures as a result of the heat treatment, were then subjected to rolling contact fatigue (RCF) tests. Those elements with a fine microstructure had nearly three times the life of those with a coarse microstructure. Retained austenite and residual stress were measured both before and after RCF at different depths below the contact surfaces.In both types of microstructure, rolling contact-induced plastic deformation tended to significantly decrease the near-surface retained austenite content. Rolling contact also tended to produce an increase in compressive residual stresses in the subsurface fine microstructure. In contrast, the residual stress state in the coarse microstructure was changed by RCF from compressive to tensile. Such differences in the residual stress and amount of retained austenite in the microstructure clearly affected the elements’ RCF life.