Study On Microstructure And Properties Of Heavy-haul U75V Rail Steel Plate By Dry Friction

The axle load and speed of heavy-loaded train are gradually increased due to the need for economic development,which could accelerate rail wear and strongly influence riving safety.Therefore,it's particularly important to study wear properties of rails under different wear conditions.In this work,GPM-30 friction testing machine is used for pure rolling test.The effects of different speed and contact stress on wear properties of U75 V steels,as well as the influence of rail corrugation formation during the wear process on the surface layer on microstructures and properties are researched.Following conclusions are summarized through many experiments:1.Microstructure of wear surface is significantly changed during pure rolling conditions.According to the characterization of structure changes,severe plastic deformation zone,flat plastic deformation zone and plastic deformation zone are consisted from the surface to matrix.In the severe plastic deformation zone,ferrite and cementite fragment seriously and fibrous structure formed,in which surface cracks generate mainly and extends along fibrous ferrite.In flat plastic deformation zone,the direction of pearlite lamella changes gradually parallel to running direction when a certain angle existed;pearlite is refined obviously until pearlite lamella direction is similar to rolling direction as same as in the plastic deformation zone.2.The influence of revolving speed on friction coefficient is not obvious regularity under pure rolling condition.However,wear loss under per unit of speed and rail corrugation enhances with the increase of revolving speed;the thickness of severe plastic deformation layer of crest decreases as opposed to trough.Revolving speed influences wave length of rail corrugations when other parameters are same.3.For different contact stress,it can be found that the influence of contact stress on friction coefficient is not evident under lower contact stress.While contact stress reaches to a certain degree,the corresponding friction coefficient under the same speed increases as well as wear loss under per unit of speed with the increase of contact stress.Meanwhile,the thickness of severe plastic deformation layer increases slowly while the thickness of flat plastic deformation layer growths rapidly;rail corrugation of samples aggravate but wave length of rail corrugation is changeless.4.According to different morphology of rail corrugation appears on wear surface,rail corrugation forming process is divided into three parts: initial stage,medium stage and later stage of rail corrugation.In initial stage of rail corrugation,adhesion wear is the main wear mechanism.In medium stage of rail corrugation,periodic rail corrugation is gradually formed on the wear surface.Wear mechanism of crest and trough is adhesion wear and fatigue wear respectively.For the later stage of rail corrugation,rail corrugation is aggravated and surface damages seriously.With the formation of rail corrugation,surface hardness of sample increase gradually.Surface hardness distributes like the wave after rail corrugation forms completely,the maximum hardness is located in trough and the minimum hardness is in crest.