Research On Wear Behavior Of Plasma Quenched Wheel-rail Materials Affected By Pre-cracks

As an important surface strengthening technology,plasma quenching has great potential in improving the wear resistance and fatigue resistance of wheel and rail materials.The damage mechanism of plasma quenching utilized on wheel and rail materials is still necessary to be researched.In this paper,the surfaces of the wheel and rail rollers were quenched by laminar plasma jet,the pre-cracks on the surface of the wheel rollers were manufactured by the electric discharge machining,the rolling contact wear tests were carried out on the MJP-30 test machine.The effect of pre-cracks on the wear behavior was studied and the damage mechanism diagrams of quenched wheel and rail materials were established.The main conclusions are as follows:For the unquenched rollers,pre-cracks significantly increase the mass loss of wheel rollers(60% to 111%)and increases the mass loss of rail rollers(46% to 62%).For the quenched rollers,pre-cracks increase the mass loss of the wheel rollers(24%?30%),and slightly increase the mass loss of rail rollers(13%?21%).For the unquenched wheel rollers,the pre-cracks are filled by the material near pre-crack with additional shear.Severe wear zones appear on the surfaces of the wheel rollers caused by the continuous accumulation of additional shear,forming an uneven wear characteristic.In addition,the increase in the depth of the pre-crack will aggravate the uneven wear characteristic.For the unquenched rail rollers,the plastic deformation of the surface layer is slightly accelerated by the impact load,slightly increasing the mass loss of rail rollers.But no uneven wear occurs on the rail rollers.For the quenched wheel rollers,no obvious plastic deformation occurs in the quenched zones,and the plastic deformation of the matrix material is slightly reduced due to the pinning effect of the quenched zone.Edge cracking in the quenched zone and the large-angle crack near pre-crack which penetrate the quenched zone are the main damage characteristic.Edge cracking is mainly caused by the thinner size of edge and the shear stress that making the edge to separate from the main body of the quenched zone with the periodic vertical load.Largeangle cracks are mainly caused by impact loads.Large-angle cracks slightly reduce the edge cracking of the quenched zones,significantly increasing the risk of large-scale peeling.Additionally,the circumferential width of shallow pre-crack increases about 51% with inner wall spalling after wear;the width of deep pre-crack narrowed about 17% with displacement of left part of quenched zone after wear.The damage characteristics of the quenched rail rollers are similar to those of the quenched wheel rollers,including the edge cracking of the quenched zone.The difference is the edge cracking of rail rollers is severer than that of the wheel rollers,which is mainly caused by the thinner depth of the quenched zone obtained by the rail material under the same process.