Abstract
Two heat-treatment routes of bainite austempering, namely above-Ms austempering and below-Ms austempering, were applied on a low carbon rail steel. The obtained multiphase microstructures containing bainitic ferrite, martensite and retained austenite were quantitatively characterized by dilatometry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. We investigated the influences of multiphase microstructure on the wear and rolling contact fatigue (RCF) behaviors in terms of weight loss, worn surface, microstructural evolution, and crack initiation. Results showed that the below-Ms austempered samples exhibit a less wear weight loss and a controllable RCF damage, compared to above-Ms austempered counterparts. The improved wear and RCF resistances of below-Ms austempered samples are attributed to the refined multiphase, increased mechanical stability of film-like retained austenite, as well as good deformation compatibility between bainitic ferrite and ductile martensite. Meanwhile, the correlations between microstructural evolution and crack initiation sites were established to discuss the competition between surface and subsurface crack initiation upon rolling contact.
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