Electron microscopy investigations of microstructural alterations due to classical Rolling Contact Fatigue (RCF) in martensitic AISI 52100 bearing steel

Substantial microstructural changes have been found to occur in bearing steels when subjected to high stress Rolling Contact Fatigue (RCF) and have been mainly reported in literature between the 1940s and 1990s. However, owing to limitations in the characterisation techniques available at the time, inconsistent interpretation and use of discrepant terminology have caused considerable difficulties in defining the microstructural changes accurately and unambiguously. In the present work, we have investigated the typical microstructural alterations, including Dark Etching Region (DER), Low Angle Bands (LABs) and High Angle Bands (HABs), and their formation mechanisms in RCF failed AISI 52100 (100Cr6) bearing steels using a combination of advanced microstructure characterisation techniques, including Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) coupled with Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), and nanohardness measurements. Based on this combined approach, we are now able to give detailed insight in the plasticity-induced transformation and degradation mechanisms during high-stress RCF. The results show that new globular and elongated grains with distinct textures form during all stages of RCF, however a redistribution of chemical elements was only observed during the later stages of RCF. This has provided a significant insight in the formation mechanisms of DER, LABs and HABs. A model of the sequence of microstructure alterations during RCF is thus been proposed based on the findings.