Spall Propagation Characteristics of Refurbished VIM–VAR AISI M50 Angular Contact Bearings

Abstract

During times of restricted supply, bearing refurbishment offers an attractive avenue to maintain operational readiness. However, bearing operation after fatigue spall initiation on refurbished bearings has not been extensively studied. In this study, spall propagation characteristics were compared between new and refurbished vacuum induction-melted, vacuum arc remelted AISI M50 208-size angular contact bearings. A control group of new AISI M50 bearings was evaluated for spall propagation characteristics as a baseline. Another group of AISI M50 bearings were subjected to an accumulated 11.5 billion stress cycles at a maximum Hertzian contact stress of 1.93 GPa and a temperature of 127 °C followed by Level II refurbishment. The refurbished bearings were evaluated for spall propagation characteristics and compared to the baseline bearings. Spalls were initiated via seeded Rockwell C hardness indents and propagated at a maximum Hertzian contact stress of 2.65 and 2.41 GPa, respectively, on both groups of bearings. The propagation rates of the bearings were measured in real time using an oil debris monitor. Pre- and post-tested bearings were examined for changes in microstructure, residual stress and retained austenite as a function of depth in the circumferential direction. No statistically significant difference in spall propagation characteristics was observed between new and refurbished bearings at the operating conditions and accumulated stress cycles studied here.