Mechanism of thermal fatigue damage in heavy haul train wheel

Heavy haul trains are subjected to high axle loads and harsh service conditions, leading to large mechanical and thermal loads on the wheel treads. Therefore, understanding the evolution of the near-surface microstructure of wheel treads and its influence on fatigue crack propagation is very important. In this study, the microstructure and fracture mechanism of heavy haul wheels subjected to fatigue fracture failure are studied in depth. The results indicate the formation of a white etching layer (WEL) and brown etching layer (BEL) on the wheel surface. On the wheel surface, martensite is refined, and the grain size is the smallest, compared to other depths. At greater depth, the microstructure of the BEL is composed of equiaxed ferrite, granular cementite, martensite, and residual austenite, which are transformed into equiaxed ferrite and granular or short-rod cementite. Fatigue cracks pass through the WEL and propagate along the interface between the WEL and BEL, and continue to propagate to the plastic deformation zone after penetrating the entire BEL. An oxide layer is formed within a certain area on both sides of the crack in the BEL and the plastic deformation zone. Numerous intersecting cracks in the oxide layer lead to continuous fracture and spalling of the material near the inner side of the crack, increasing the width of the crack gap and accelerating spalling of the wheel material.