Research On Microstructure And Properties Of D2 Wheel Steel After Ultrasonic Rolling

With the continuous development of rail in China,the wheel-rail system,which is the main operating system,directly affects the lives and property safety of passengers.Therefore,research on improving the wear resistance and fatigue life of the wheel-rail system is still a key issue.In this test,the surface ultrasonic rolling of D2 wheel steel was performed.The optimal processing parameters were obtained through orthogonal optimization tests.The effects of surface texture and surface morphology of the two samples before and after processing were compared.The friction and abrasion test and rolling contact fatigue test were performed on the two specimens using the GPM-30 friction and wear tester,and the effects of surface ultrasonic rolling technology on the mechanical properties of D2 wheel steel were compared and analyzed.Results surface:The main parameters that affect the surface roughness,surface hardness,circumferential residual stress,and axial residual stress of D2 wheel steel are feed,static pressure,spindle speed,and static pressure,respectively.Surface ultrasonic rolling technology will reduce the surface roughness of D2 wheel steel,increase surface hardness and surface residual stress.Ultrasonic rolling makes the surface grains of the sample finer,increases the content of large-angle grains in the surface structure,and forms a fine-grained layer with higher hardness.The best surface ultrasonic rolling process parameters to obtain excellent structure and performance are static pressure 0.4MPa,feed rate 0.05mm/r,and spindle speed 70r/min.Surface ultrasonic rolling technology will delay the appearance of multiple wheel changes.Before the occurrence of multiple changes,the initial wear and 3×10~5r wear samples were observed.The wear amount and friction coefficient of the ultrasonic rolled samples were always slightly lower than the original samples.After the changes,the two samples gradually tended at the same level.The wear mechanism of both samples is adhesive wear and oxidative wear.When there are multiple changes,abrasive wear is introduced,so the surface ultrasonic rolling technology will not change the wear mechanism of D2 wheel steel.During the 3×10~5r high-cycle wear process,the plastic deformation layer of the ultrasonic rolled sample is about 26?m,and the original sample is about 20?m.The thicker deformed layer has a deeper depth of effective hardened layer and anti-vibration ability,which delays the appearance of multiple changes.The correct selection of process parameters for ultrasonic rolling will improve the fatigue life of D2 wheel steel by increasing the surface hardness and stress,reducing surface roughness and other advantages,up to 2.3 times the original sample.Excessive static pressure parameters will produce micro-cracks on the surface of the sample,reducing fatigue life.The fatigue process of the original sample and the ultrasonic rolling sample are four processes:micro damage,crack initiation,crack propagation and spalling.The superficial cracks of the ultrasonic rolling specimens originate on the surface of the fine-grained layer and propagate in the fine-grained layer;no matter whether the ultrasonic rolling process is carried out,the fatigue crack propagation mechanism is the same,the direction of expansion is 30°?45°from the running direction angle,and extend to the core or surface of the sample along the interface of proeutectoid ferrite or pearlite and proeutectoid ferrite.