Impact Wear Behavior Of Hypereutectoid Steel Rail Welded Joints Welded By Flash Welding And Aluminothermic Welding

As the railway is developing towards the direction of high speed and heavy load,the continuous increase in train speed and axle weight makes the assessment of the basic parts of train running more severe,especially the safety and stability of rail joints,especially the safety and stability assessment tests of rail joints.With the emergence of seamless lines,the impact of wheels on rail joints is greatly alleviated,so that the train can run steadily and continuously for a long time according to the stipulated speed,which extends the operating life of railway line equipment and train vehicles.However,due to the influence of welding flux,high temperature and post-welding heat treatment,the microstructure and mechanical properties of rail welded joints are significantly different from the base material,which has become a weak link in seamless railway.Therefore,the research on rail welded joints damage will improve the safety and service life of the whole railway.However,the impact wear properties of rail welded joints under different welding processes are seldom studied.In this paper,the difference in microstructure of hypereutectoid steel rail welded joints welded by flash welding and aluminothermic welding was analyzed.Using our homemade impact wear tester,the evolution process and wear mechanism of impact damage of hypereutectoid steel rail welded joints in welding seam,softening part of heat-affected zone and base material under different impact force and impact cycle times were studied by simulating the impact of the wheel passing through the rail joint.The results are expected to provide theoretical basis for the improvement of rail welding process and the adjustment of train operation scheme.The main conclusions are as follows:1.The impact wear degree of rail welded joints increased with the increasing impact cycle and impact load.The impact wear of welded joints experienced the evolution process of plastic deformation,partial pitting failure,fatigue crack generation and spalling,which is the result of the combined action of fatigue wear and oxidative wear.2.With the increase of the impact cycle,the growth trend of impact wear volume in different areas of flash welding and aluminothermic welding joints was from urgent to slow.In addition,compared with the slow growth of flash welding in the later period of impact,the wear volume of aluminothermic welding increased significantly with the increasing of impact cycle.Under the low impact load and low impact cycle times,the fatigue resistance of flash welding was better than that of aluminothermic welding.When the load impact increased to800 N or more,the wear degree of the softened part of the flash welding joint in the heat-affected area was more obvious than that of aluminothermic welding under the same condition.3.By comparing the two welding processes,the degree of wear increased in order to the base material(BM),flash weld zone(FW),aluminothermic weld zone(AW),flash welding heat-affected zone(FH)and aluminothermic welding heat-affected zone(AH).With the increasing impact cycle and impact force,the wear mechanism of rail base material zone was changed from adhesive wear to fatigue wear,while the wear mechanism of welded joint weld zone and heat-affected zone was changed from material spalling to fatigue wear.4.There were several internal cracks in the heat-affected area of the joints of the two welding processes,which interacted with each other and developed towards the material,eventually leading to the stripping of a large volume of material.