Relationship Between the Microstructural Evolution and Wear Behavior of U71Mn Rail Steel

During train operation in a wheel-rail system, the service lives of the wheel and rail materials are heavily influenced by microstructural evolution. This study investigated the relationship between microstructural evolution and the wear properties of U71Mn rail steel under conditions of dry sliding wear using an MRH-5A wear tester. The results demonstrated that tribological white etching layers (T-WELs), which comprise nanocrystalline α-Fe and fine carbide, are formed after a certain number of cycles. The T-WEL thickness increased with the number of cycles; however, more cycles caused T-WEL flaking, which resulted in a reduced T-WEL length. The high microhardness of T-WELs (approximately 950 HV) is mainly attributed to ferrite grain refinement and cementite dissolution. During initial wear, the existence of grinding marks on the surfaces of the samples indicated an obvious increase in the wear loss of the steel. The high microhardness of the T-WELs can enhance wear resistance; thus, as the number of cycles was increased, the wear loss of the steel was reduced. At this point, an adhesive wear mechanism acted on the rail steel. The formation of fatigue cracks at the interface between the T-WEL and the plastic deformation layer induces T-WEL flaking, which increases wear loss. Consequently, after 6000 cycles, wear loss increased as the wear mechanism changed to fatigue wear. It is confirmed that T-WEL flaking is the primary cause of wear failure in U7Mn rail steel.