Contact Fatigue Behavior And Microstructure Evolution Of HighSpeed Train Wheel

For the purpose of solving the problems that wheel-rail system faced with under the high speed-overload conditions,GPM-30 contact fatigue test machine was used to simulate the wheel/rail operation test with the materials of domestic D2 wheel steel.The surface micro-structure and property of D2 and running failure ER8C wheel that imported from Europe were then characterized and analyzed through optical microscopy(OM),durometer,scanning electron microscopy(SEM),transmission electron microscopy(TEM),etc.It emphatically analyzes the failure process of the wheel material and white etching layer(WEL)formation mechanism from the perspective of micro-structure and property evolution.And deep research about the influence that surface micro-structure have on contact fatigue behavior was made.The WEL on high speed train wheel is mostly discontinuous lamina under the optical microscope.It's withe under the OM because it's difficult to corroded by natal.Under the SEM,WEL on wheel flange is mainly consist of three kinds of mcro-structure:nanocrystalline caused by plastic deformation and fragmentation,ferrite nanocrystalline caused by dynamic recrystallization,martensite/bainite with ultra-fine original austenite grain.Above three are of nanometer level ultrafine organization.It's analysised that the reason why phase transformation WEL has higher hardness than general quenching organization is that WEL has ultrafine organization.The three kinds of formation mechanism of WEL are as follow:force effect based mechanism,heating-force effort combined mechanism,heating based mechanism.Because of the limitation of the temperature and stress influence depth,the micro-structure from the surface to the core change correspondingly:the closer to the surface the greater the plastic deformation is,the higer the level of the instantaneous austenitizing,and the less unfused carbide it has.WEL influence the later running in two ways:on the one hand,the high hardness of WEL could enhance the wear-resisting property of the wheel,on the other hand,the brittleness of the WEL will make the interface between it and matrix a fatigue crack initiation or lead to surface material spalling.Contact fatigue sample at first have slight corrugation and then be rub down,finally a severe corrugation accur,friction factor increase sharply and contact fatigue failure happened.The corrugation firstly happened at one or more point,and as the cycle number increase,the coorugation point extend to the whole tread.The peak is somth and spall little.The region of valley have spalling which have 63° angle with running direction.At low magnification,the valley has sweel-and-swale morphology.The sweel place are smooth and the swale place are full of delamination.Plastic deformation WEL and martensite WEL structure was found at the surface of the contact fatigue sample,the formation mechanism is temperature-based mechanism.The micro-failure mode of high speed train wheel could mainly conclude as follows:Hardening layer peeling because of the existence of WEL(overall spall along the interface/the intergranular spalling in the WEL),shallow peel along the plastic deformation organization.Once the crack along the interface originate,it will spread rapidly.lt also explains that WEL structure has high hardness and low ductility and toughness and has great difference with plastic deformation structure in various property.