Influence of slip ratio on worn-surface microstructure and fatigue wear behavior of D2 wheel steel

To investigate the worn-surface microstructure and fatigue cracks in D2 wheel steel under the pure rolling and 0.5% slip ratio conditions, a rolling wear test using a GPM-40 wear machine to simulate the wheel/rail operation was performed. After testing, a transmission electron microscope, a scanning electron microscope with electron backscatter diffraction, and micro-hardness testers were used to characterize the microstructure and fatigue cracks. The surface microstructure and hardness of the pure rolling sample were in a steady state after 8x10(4) cycles; however, the 0.5% slip ratio sample reached a steady state after 7x10(3) cycles. Regardless of whether the test uses the slip ratio, the orientation of lamellar pearlites gradually became parallel to the surface and a portion of lamellar cementites was fragmented and dissolved during the formation of steady-state microstructure. The slip ratio accelerates this process. The hardening mechanism of the samples shows a decrease in the lamellar spacing of pearlite and the refinement of proeutectoid ferrite (PF). As the number of cycles increased, plastic deformation of samples became increasingly severe and the wear mechanism of the samples was fatigue wear in steady state. The sample surfaces formed shallow cracks, which gradually peeled off. The slip ratio accelerated the initiation and propagation of fatigue cracks because of the high friction stress on the contact surface. Most fatigue cracks initiated at the interface of pearlite and PF and in the PF region.