Research On Welding Of High Strength Pearlite And Bainite Dissimilar Rail

In recent years,with the high-speed development of heavy haul railway,the requirements for the bearing capacity of rail are becoming higher and higher.The construction of heavy haul line engineering requires rails with higher strength and better wear resistance.Its bainite rail has great development potential and has become a research hotspot in various countries.At present,bainite rail has been used in turnout area and achieved good results,but pearlite rail is still mainly used in heavy haul lines at home and abroad.In order to realize seamless rail in turnout area and replace high wear-resistant bainite rail in sections on line curve,it is necessary to solve the problem of heterogeneous rail welding.GPW-1200(75)pneumatic welding machine is used to explore the weldability of U95 Cr pearlite rail and U20 Mn bainite rail by using the mature 75 N U95Cr pearlite rail pneumatic welding process for reference,which has important theoretical significance and engineering application value for the application of bainite rail in the construction,operation and maintenance of heavy haul line engineering.In this paper,75 N U95Cr and U20 Mn dissimilar rails are welded by pneumatic welding.It is found that a good metallurgical joint can be obtained,and the microscopic characteristics of the weld are straight and thin lines;The mechanism of metallurgical bonding is that under the action of welding thermal mechanical cycle,atomic diffusion first occurs between the metals at the end face to be welded,and common grains are formed through interface nucleation and micro hole elimination.Finally,the alloy elements at the weld interface tend to be uniform.The mechanical property test shows that the tensile strength of the welded and normalized joints are 972 MPa and 1063 MPa respectively,the elongation is 5.8% and 6.2%respectively,and the i MPact energy is 3.15 J and 3.81 J respectively.The hardness HJ/Hp of the rail top surface is in the range of [0.99,1.07].The hardness of the joint is equivalent to that of the base metal.After normalizing,the tensile strength,elongation and i MPact toughness of the joint are improved,the overall hardness of U95 Cr side is improved,and the overall hardness of U20 Mn side is reduced.There is 66.2% martensite structure in the weld on U20 Mn side,which is the reason for the low i MPact toughness.In view of the main quality problems existing in the joint rail foot,this paper designs and puts forward the technical scheme of adding restraint blocks to the joint rail foot to ensure the upsetting and extrusion deformation degree of the joint rail foot and improve the foot collapse.The optimal test results show that the right rail foot of the welded 7# joint has no foot collapse defect,there is no micro smooth area on the fracture,the micro morphology of the weld interface changes from fuzzy black line to straight thin line,and there is no micro hole under the electron microscope.