In a previous study, we developed a novel in situ analysis and observation system that allows for simultaneous synchrotron X-ray diffraction (XRD) and optical observations of a frictional surface. This in situ system was used to investigate the scuffing phenomena of SUJ2 bearing steel (AISI 52100); characteristic surface deteriorations occurred during the scuffing process, including plastic flow, heat-spot formation, austenite transformation, and a decrease in the width of the XRD peaks (indicating a decrease of dislocations and strain). These surface deteriorations are not observed during normal wear, hence it is possible that they cause catastrophic wear during the scuffing of steel. In this study, to elucidate the scuffing mechanism of steel, we focused on the following two points: (1) whether the above surface deteriorations are unique to SUJ2 steel or whether they occur in general steels as well, and (2) the extent to which these surface deteriorations contribute to the wear amount. To achieve these objectives, we performed scuffing tests on four types of steel using the previously developed in situ system. In particular, we focused on the first stage of the scuffing process. The present test results suggest that these surface deteriorations also occur in general steels, and that plastic flow and heat-spot formation, which originate from the same phenomenon, are the dominant contributors to the wear amount during the scuffing of steel. Furthermore, the wear amount per unit plastic flow appears to be independent of steel composition.
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