Influence of Residual Stress and Temperature on the Cyclic Hardening Response of M50 High-Strength Bearing Steel Subjected to Rolling Contact Fatigue

Microstructural and mechanical characterization investigations on three variants of a through-hardened M50 bearing steel are presented to compare and contrast their performances under rolling contact fatigue (RCF) loading. Baseline (BL) variant of M50 steel bearing balls is subjected to: (i) a surface nitriding treatment and (ii) a surface mechanical processing treatment, to obtain distinct microstructures and mechanical properties. These balls are subjected to RCF loading for several hundred million cycles at two different test temperatures, and the subsequent changes in subsurface hardness and compressive stress-strain response are measured. It was found that the RCF-affected subsurface regions grow larger in size at higher temperature. Micro-indentation hardness measurements within the RCF-affected regions revealed an increase in hardness in all the three variants. The size of the RCF-affected region and intensity of hardening were the largest in the BL material and smallest in the mechanically processed (MP) material. Based on Goodman's diagram, it is shown that the compressive residual stress reduces the effective fully reversed alternating stress amplitude and thereby retards the initiation and evolution of subsurface plasticity within the material during RCF loading. It is quantitatively shown that high material hardness and compressive residual stress are greatly beneficial for enhancing the RCF life of bearings.