Study On The Contact Fatigue Performance And Evolution Of Microstructure Of D2 Wheel Steel

In our country,railway plays an irreplaceable role in both passenger transport and freight transport.The critical component to realize the traction and braking of the train is wheel,which has a significant impact on maintaining the safety of the train and the normal operation of the railway transport.With the rapid development of high-speed railway in our country,the speed of the train increases continuously,which causes the deterioration of the wheel’s service condition.Consequently,the failure of the wheel becomes more and more serious,such as contact fatigue damages.Moreover,it is of great significance to the development of the railway to realize the localization of high-speed train wheel.Therefore,to explore the generation mechanism of the fatigue and improve the anti-stripping property of the wheel has becomes the focus of the railway workers.In this experiment,contact fatigue tests under the conditions of different contact stresses are investigated by using the GPM-30 Rolling Contact Fatigue Tester.Then,the failed D2 wheel steel generated from the analog wheel operation is analyzed using machinery such as Optical Microscope,Scanning Electron Microscope,Vickers Indenter,etc.Meanwhile,the contact fatigue properties and their relation with surface structure are studied.The results show that the fatigue limit of the D2 wheel steel is 1290 MPa under the rolling-sliding condition that the rotate speed is 1440r/min,slip ratio is 0.5%,and the lubricating roil is No.20;the main failure form of D2 wheel steel under different contact stresses is the typical V-shaped spalling fatigue.mechanical grinding of the original samples will cause plastic deformation of the surface of the pearlitic D2 wheel steel and generate fine sub-grain with a thickness of 0.5~1.5μm(/grain),and microcrack and small chipping pit are formed in this plastic deformation layer in the process of rolling-sliding,than Becomeing the fatigue source of contact fatigue damage.there are four phases in the formation of contact fatigue damage including the formation of microcrack and small pitting,the formation of main fatigue crack,the propagation of main crack,the formation and propagation of secondary crack and the fatigue spalling.The last three phases are concerned with the alternating stress of the material surface and hydrodynamic effects caused by lubricating oil.Fatigue crack preferentially propagates along the interface between the proeutectoid ferrite and the pearlite.The sub-grain of proeutectoid ferrite in the surface layer is refined by the plastic deformationand the most refinement appears in subsurface.Tne trend of Microhardness from the Surface to the core increased at first,than fall to the original hardness.The maximum principle sheer stress calculated also appears in subsurface.which demonstrates that the changes of the surface structure morphology and hardness are caused by principle sheer stress.