Complex interaction behavior of rolling contact fatigue/wear of U76CrRE heavy rail steel

Rolling contact fatigue and wear failure are the most common forms of failure in heavy rail steel. However, the complicated relationship between fatigue and wear of heavy rail steel remains largely unexplored, with the failure mechanism yet to be fully understood. To investigate the damage and surface microstructure evolution in pearlite rails under rolling contact fatigue and wear interactive loads, a study was conducted on U76CrRE pearlite heavy rail steel, both rolled and heat-treated. The research utilized various methods, including rolling friction and wear testing, laser confocal microscopy, scanning electron microscopy, and electron backscatter diffraction, to measure and observe the wear rate, surface damage, deformation layers, and crack initiation and propagation in heavy rail steel with and without precast cracks. The study quantitatively analyzed the microstructural evolution and failure behaviors of pearlite rail under wear and fatigue interaction loads. The results show that the deformation layer in rolled heavy rail steel is larger than that in heat-treated specimens, especially when there are no precast cracks or the depth of such cracks is less than the wear layer. However, the wear rate and deformation layer in rolled rails were found to exceed those in heat-treated rails. The ferrite in pearlite near the deformation layer is refined and mixed with similarly refined cementite particles. Initially, ferrite grains exhibit mainly small-angle grain boundaries, but as the distance from the surface layer increases, the proportion of large-angle grain boundaries grows, leading to cracks characterized by larger angles, greater depths, and shorter lengths. Conversely, cracks in heat-treated rails are characterized by smaller angles, shallower depths, and longer lengths, with a more pronounced trend of crack propagation compared to rolled rails. When prefabricated crack depth exceeds the wear deformation layer, these cracks expedite wear mechanisms, encouraging the rapid generation and propagation of fatigue cracks and hastening fatigue failure. The cracks tend to demonstrate larger angles, deeper depths, and longer lengths, indicating that both rolling and heat-treated pearlite heavy rails are mainly subject to fatigue failure, with crack propagation being more evident in rolled rails than in heat-treated ones. Furthermore, when rails are matched with wheel steel of higher hardness, the crack angle, depth and length of rails become more pronounced than those with lower hardness. Moreover, the duration of the rail wear mechanism is prolonged.