Experimental Study On Friction And Wear Of Heavy-Haul Railway Wheel And Rail Materials

With the development of heavy-duty railway technology and the demand for transportation efficiency and reduced operating economic costs,the axle load of heavy-duty railways in China has been increasing in recent years,but amount of problems of the contact of wheel and rail materials in field have emerged.Reasonable selection and proper matching of wheel and rail materials are of great significance for balancing wheel and rail wear,increasing the service life of wheel and rail materials,and reducing maintaining costs while ensuring the safe running of trains.In this paper,a laboratory study is conducted for investigating the problem of wheel-rail materials matching in heavy-haul railways and evaluating the friction and wear properties of different wheel-rail material combinations.The present work researched the friction wear and contact fatigue performance of four types of pearlite rails,U75V(heat treatment rail),U75V(hot rolling),U78CrV(heat treatment),U78CrV(hot rolling),and two types of pearlite wheels: CL60 wheels and CL70 wheels.Design different contact stresses and slips to conduct laboratory research to explore the wear properties of bainite rails;compare and analyze the wear and the resistance of contact fatigue of different steel grades,and the main conclusions are as follows:(1)From the perspective of wear,U78CrV(heat-treated rail)has the best wear resistance;the best combination of wheel and rail materials is U78CrV(heat treatment rail)-CL60 wheel and U78CrV(heat treatment rail)-CL70 wheel,the enhancement of hardness of wheel material resulted in the increasing wear for the rail materials,but the harder wheel has the better wear resistance.The friction coefficient of the contact interface between different types of pearlitic rails and CL70 wheels is about 0.45,the friction coefficient of the experimental group with the friction pair of CL60 wheels is 0.375.The friction coefficient of the contact interface between the same kind of rail and different types of wheel materials is quite different.The damage types of wheel and rail contact surface under the normal stress of 1430 MPa and 2% slip are mainly rolling contact fatigue damage such as peeling and peeling,and the main form of wear is contact fatigue wear.It can be concluded that the depth of the work hardened layer of the rail specimen is inversely proportional to its own hardness.Because the crack length and depth are the smallest,it indicates that U78CrV(heat treatment rail)has good resistance to rolling contact fatigue.In addition,when the wear system is the combination of pearlitic rails and CL70 wheel,cracks on the surface layer of the rail are more likely to penetrate into the matrix.(2)As contact stress and slip ratio increase,the amount of wear on bainite rails and CL60 wheels also increases.When the bainite rail sample and the CL60 wheel sample are subjected to rolling wear,the value of the friction coefficient between the contact interfaces is inversely proportional to the normal contact stress between the two samples,that is,as the contact stress increases,the friction coefficient decreases.At the same time,the friction coefficient is proportional to the slip ratio.When the slip rail increases,the friction coefficient also increases.Compared with the increase in slip,the increase in contact stress has a stronger effect on the plastic flow of bainite steel and the initiation and propagation of cracks.The contact fatigue wear mechanism plays an important role under lower slip ratio(2%),but under higher slip ratio(10%)conditions,the main wear mechanism changes to abrasive wear,and the wear resistance of bainite steel in abrasive wear mode is more poor,not suitable for small radius curves with high slip ratio.(3)By comparing the average wear rate of 5 kind of high-strength rails,it is found that although the bainite rail has a high initial hardness,its wear resistance is far inferior to the other four types of pearlitic rails under large axle load.During the running-in phase,the friction coefficient showed a trend of increasing first and then decreasing.The friction coefficient basically remained unchanged after reaching the stage of stable wear.The speed of reaching the depth limit of the work-hardened layer depends on the initial hardness of the steel base material.The crack depth and length of the bainitic rail are smaller than the pearlitic rail in the early stage of wear,under the same conditions,the time for the crack of the bainitic rail specimen to reach the maximum value is longer.(4)Comprehensive consideration of wheels and rails system wear and surface damage,the combination of U78CrV(heat-treated rail)+ CL60 wheels is the best and most reasonable match.