Research On Solid Phase Welding Of 60 Kg/m Bainite And Pearlitic Rails

With the development of railway transportation,bainite rail with high strength,toughness and wear resistance has a good application prospect.At present,the rails used in high-speed railway,heavy-haul railway and plateau line are all pearlite rails.In the future application of bainite rails,the first problem to be solved is the dissimilar rail welding when connecting with existing lines,which is a technical bottleneck in the field of rail welding that needs to be broken through.Therefore,this paper carries out preliminary tests to study the welding process suitable for bainite rail and pearlite rail,and to explore and solve the technical problems of how to obtain high quality welding joints in accordance with rail welding standards.Gas pressure welding belongs to solid phase pressure welding,which has strong applicability and wide technological parameters and is widely used in rail welding engineering.It is suitable for dissimilar rail welding.In this paper,the welding process of U26 Mn bainite rail and U75 V pearlite rail is studied by using GW-1200 rail gas pressure welding machine.OM,SEM,impact,tensile and hardness tests were used to investigate the metallurgical bonding characteristics and mechanical properties of joint interface of air pressure welding joint of dissimilar rail,providing important technical support for the future application of bainite rail.The results show that the element diffusion behavior exists on both sides of the weld interface,and the metal in the weld interface is dynamically recrystallized under the action of thermo-mechanical cycle to realize metallurgical bonding.The microstructure of U75 V rail side is pearlite and ferrite,and the fine grain zone formed by dynamic recrystallization can be observed near the weld interface.The microstructure of U26 Mn side is bainite ferrite,residual austenite and martensite.The average strength of welded joint is more than 85% of U26 Mn rail base material,and the joint strength is further improved after normal heat treatment,while the average impact energy of welded joint and normal joint is lower than the standard requirements.The average hardness of joint rail top surface and softening zone,the width of softening zone are all meet the requirements of TB/T1632,and after normalizing treatment,the softening zone of the joint is significantly reduced.The drop weight test of welded joint is not qualified,the reason is that there is drop deformation of joint rail foot,the fracture of rail foot crack source is smooth,and the combination degree is poor,which greatly affects the drop weight performance of joint.Aiming at the problems of poor joint quality and joint deformation of rail bottom foot,the constraint part of rail bottom foot is designed and the relevant experimental research is carried out.The results show that the amount of joint collapse can be reduced by adding the constraint part of rail bottom foot,and the minimum collapse of rail bottom on both sides of joint is 0.5mm,which meets the engineering requirements.The maximum tensile strength of rail bottom foot is 1110 MPa,which is consistent with the strength of other positions of the joint,indicating that the weld interface of rail bottom foot can achieve good metallurgical bonding under constraint conditions.