Study On Impact Wear Properties Of Frog Bainite-Pearlite Dissimilar Rail Weld Joints

With the development of the railway with heavy load and high speed in China,the damage of the wing rail of the frog is becoming more and more serious.At present,the use of bainite steel in wing rail reduces the damage degree and further improves the overall service life.This involves the structural strength and wear resistance of the weld joint between rail and bainite steel wing rail.Due to the characteristics of the frog structure,its wheel-rail force is often several times that of other sections.When the dissimilar rail weld joint is not smooth due to different wear resistance,it will be further affected by strong impact load,resulting in fat edge and collapse and other damage.At present,the research on impact wear resistance of rail weld joint at home and abroad seldom involves bainite-pearlite dissimilar steel frog.Therefore,it is of great significance to study the wear resistance of the dissimilar rail weld joint,especially the wear mechanism of the heat affected zone,for improving the overall strength of the frog,further improving its service life and ensuring the safety of train.In this thesis,the homemade impact wear test machine is used to simulate the impact contact of the train passing rail weld joint,and the impact test under different impact times on the two groups of dissimilar rail weld joints of the frog with welded and normalized is carried out respectively.The changes in the microstructure,surface hardness,wear volume and surface morphology of the softened zone of heat affected zone,overheated zone of heat affected zone,weld zone and base material zone of the weld joints were compared and analyzed,and combined with finite element simulation results,the damage evolution process and the wear transition mechanism of the different zones of the weld joints with the increasing number of impacts are studied.The main research conclusions are as follows:1.With the increase of the number of impacts,the surfaces of two groups of frog bainite-pearlite dissimilar rail weld joints experience the processes of plastic deformation,the formation of work hardening layer,pitting and crack of hardening layer,peeling of hardening layer at the intersection of cracks,and appearance of secondary cracks after peeling of hardening layer.The wear mechanisms in different zones of the two groups of weld joints are slightly different: The wear mechanism of pearlite rail and bainite rail base material zone changes from surface fatigue wear in the early stage of the test to peeling wear in the late stage of the test;the wear mechanism of the weld zone and the overheated zone of bainite rail heat affected zone changes from surface fatigue wear in the early stage of the test to the coexistence of peeling wear and fatigue wear in the middle stage of the test,and to fatigue wear in the late stage of the test.All zones are accompanied by oxidation wear during impact.2.The impact wear resistance of welded joint in different zones from strong to weak is as follows: bainite rail base material zone > pearlite rail base material zone > softened zone of pearlite rail heat affected zone > softened zone of bainite rail heat affected zone >overheated zone of pearlite rail heat affected zone > weld zone > overheated zone of bainite rail heat affected zone.The impact wear resistance of normalized joint is basically the same as that of welded joint except that the impact wear resistance of the softened zone of bainite rail heat affected zone and the overheated zone of pearlite rail heat affected zone is better than that of the softened zone of pearlite rail heat affected zone.Compared with the corresponding zone of the welded joint,the damage degree of most zones of the normalized joint is reduced,and the impact wear resistance of the normalizing joint is better than that of the welded joint.The results show that normalizing heat treatment after welding can improve the impact wear resistance.3.Compared with the impact wear performance of pearlitic rail,bainitic rail has higher hardness,smaller wear volume in the early stage of impact test,less impact damage,and better impact wear resistance.But with the increase of impact times,stability of block retained austenite in the microstructure decreases,hard brittle martensitic transformation is easy to occur under high stress,can not effectively absorb the impact energy and blunt crack,the work hardening rate of the contact part faster,and crack and material spalling phenomenon are more likely to occur on the surface in the middle and late period of the test.4.Finite element simulation results show that the contact stress,surface residual stress and equivalent plastic strain are positively correlated with impact force,negatively correlated with impact ball radius,and have no correlation with impact distance.The impact deformation depth of the simulation area is in descending order: softened zone of pearlite rail heat affected zone > pearlite rail base material zone > softened zone of bainite rail heat affected zone > bainite rail base material zone;the simulation result is the same as the test wear depth in the corresponding zones of the two groups of weld joints when the number of impacts is 100,000.Simulation results have a certain reference value for predicting the impact behavior of the weld joint.