Effect of non-uniform microstructure on rolling contact fatigue performance of bainitic rail steel

Rolling contact fatigue (RCF) is the main failure mode of wheel-rail system. In this work, the influence of nonuniform microstructure on the rolling contact fatigue performance in bainitic rail steel was investigated. According to the results, an increase in degree of segregation enabled material to improve the wear resistance through the improvement of the local hardness of the rail, but seriously reduced the rolling contact fatigue performance of the rail. The crack propagated along the segregation band, thereby leading to the failure of the specimen. The main cause of fatigue crack initiation was the non-uniform strain distribution under cyclic loading due to different hardness values between the matrix and the segregation region. A large number of dislocations produced by plastic deformation on the surface of the specimen segmented grains into nanocrystals. Meanwhile, it can be seen from the in-situ heating transmission electron microscope (TEM) that the friction heat generated during RCF test was enough to support the occurrence of dynamic recovery.