Residual stress formation and stability in bearing steels due to fatigue induced retained austenite transformation

In this work, for development and sustainability of compressive residual stresses (RS) in bearing steel materials is examined. Of particular interest is the role of retained austenite (RA) transformation in fatigue performance. Cyclic torsional loading was performed for a prescribed number of cycles at specific stress levels. Specimens were then examined using X-ray diffraction techniques to observe RS values and RA volume fraction. Based on the experimental results, an empirical model incorporating RA transformation and material relaxation was developed to predict RS formation. The results obtained from the model corroborate well with experimental measurements. Experimental results indicate that much of the RA present is not useful for generating compressive RS. However, by controlling applied loading, compressive RS can be generated and maintained throughout fatigue life. These findings were then translated into rolling contact fatigue (RCF) scenarios to identify loading conditions to maximize the benefits associated with RA transformation. The experimental and modeling results highlight the utility of RA transformation in increasing compressive residual stresses within the material, but emphasize the limitations of RA in the system.