Study On Rolling Fatigue Wear Of CL65 And ER8 Wheel Steel

The train speed keeps rising as China’s high-speed rail system develops quickly.One of the primary failure mechanisms of wheels is fatigue failure.One of the reasons of wheel fatigue failure is the alteration in surface structure during wheel operation.In order to improve the design of wheel processing technology,it is crucial to investigate the evolution of the surface microstructure and the fatigue performance of wheel steel throughout the friction and wear process.Two pairs of wheel/rail materials,CL65/U75V and ER8/U71Mn,were selected from heavy haul and high-speed trains,respectively.Pure rolling wear tests were carried out on a GPM-40 rolling contact fatigue tester.The surface morphology,surface microstructure and fatigue wear cracks of the worn samples were systematically analyzed by scanning electron microscopy,three-dimensional video microscopy,roughness tester and microhardness tester.The relationship between the initiation and propagation of fatigue wear cracks and the microstructure evolution and material hardening during wear was clarified.The results show that:1.under the same experimental conditions,the change rules of wear loss of CL65 and ER8 wheel steel and rail steel are basically the same.Wheel steel always has a higher wear loss than rail steel,and CL65 wheel steel always has a lower wear loss than ER8 wheel steel.2.The main wear mechanisms of CL65 wheel steel and ER8 wheel steel before running at 0.5×10~4r are adhesive wear and abrasive wear.Both of them show obvious fatigue wear at 0.5×10~4r,but the fatigue wear crack amount and depth of CL65wheel steel are much larger than that of ER8 wheel steel,and the fatigue wear phenomenon is serious.3.When fatigue wear occurs,the surface hardness of CL65 wheel steel sample is between 320-390 HV,and the ER8 wheel steel sample has a surface hardness of 350-390 HV,which is between 32.9%and 42.3%harder than the original sample surface,respectively.The two wheel steel samples’surface microhardness and hardened layer depth are growing as the number of running cycles rises.The hardening rate is relatively large before fatigue wear,and then the hardening rate becomes slower.4.Due to the high hardness of the fine grain layer on the surface of CL65 wheel steel it can resist plastic deformation during operation,resulting in slower plastic deformation and slower hardening rate than ER8.The surface hardness of ER8wheel steel is always greater than that of CL65 wheel steel during 6×10~4r operation,and the surface hardness of ER8 wheel steel is close to saturated hardness at 6×10~4r cycles.During the formation of fatigue wear,the wear surface structures of CL65 and ER8 are basically the same,which are composed of refined ferrite grains and granular cementite.5.The plastic deformation process of the structure is sheet cementite elongation,torsion and fragmentation.The massive ferrite is gradually elongated into fibrous and the grains are refined repeatedly.6.Due to the presence of the machined fine-grained layer,CL65 wheel steel is more likely to develop fatigue wear cracks inside the fine-grained structure or at the junction between the fine-grained structure and the deformed structure,which leads to shallow peeling,or the fine-grained layer peeling.When there is no fine grain structure,the crack propagates along the fiber direction,which also causes shallow peeling.After running at the same time,the overall surface crack depth and length of ER8 wheel steel are smaller than those of CL65 wheel steel,and the trend of surface peeling is also later than that of CL65 wheel steel.