The Influence Of Surface Microstructure On The Rolling Contact Fatigue Performance Of D2 Wheel Steel

In recent years,with the rapid development of railway in our country,the speed of trains has been increased continuously,so the high-speed railway has become the key point in the development of railway at this stage.Wheels are key components of railway trains,which also has a major impact on the safety of trains and the normal operation of rail transport.Rolling contact fatigue damage is one of the main causes of whee]failure in many wheel-rail damage phenomena.Material failure usually occurs on the surface of the sample,so the work aimed to analyze the effect of surface microstructure on the rolling contact fatigue performance of D2 wheel steel and improve the resistance of wheel material fatigue performance.lt has important reference significance for the production of wheel materials and the safe and stable operation of trains.In this paper,the grinding and polishing methods are used to obtain the grinding D2 wheel steel specimens with the fine-grained microstructure and the polishing D2 wheel steel specimens which the surface microstructure is the same to the matrix.Rolling contact fatigue test was carried out on the two specimens under the same parameters using GPM-40 rolling contact fatigue tester.After the fatigue test,cracks and surface microstructure of the two specimens were observed by means of optical microscope,scanning electron microscope,the hardness distribution and roughness were also measured.The results show that the rolling contact fatigue life of the grinding sample is about 2.5 ×106 revolutions,The rolling contact fatigue life of the polished sample is about 1.7 ×106 revolutions under the conditions of contact stress of 1350 MPa,rotation speed of 1440 r/min,slip ratio of 0.5%and the lubricating oil is No.20.There was a fine-grained layer of about 1?m on the surface of the grinding specimen.During the fatigue test,the micro-cracks in the fine-grained layer initiated and propagated to form spallings which were smaller than the thickness of the fine gain layer,Then the fatigue cracks were initiated in the region where the fine gain layer was spalled,while the fatigue cracks were initiated directly on the surface of the polished specimen.The fatigue cracks were initiated at the boundary of pearlite and proeutectoid ferriteor and inside proeutectoid ferrite,with the increase of the revolutions,the interior of the pearlite cluster began to initiate fatigue cracks.These fatigue cracks propagated toward the surface at an angle of about 30°?40°to the internal and tended to propagated in the interior of proeutectoid ferrite and the boundary between pearlite and proeutectoid ferrite.Plastic deformation and hardening occured in the near surface area of the specimens.The surface hardness of polished specimens increased continuously,while that of grinding specimens rose first,then decreased and then slowly increased.Finally both of them remained stable at 450HV.The crack initiated when the surface hardness of both specimens reached about 400HVGrinding fine gain layer microsturcture can effectively delay the initiation time of fatigue crack and improve the fatigue resistance.