Research On Gas Pressure Welding Process Of High Abrasion Resistance And Obdurability Railways

With the continuous improvement of heavy-haul railway road freight volume and road service life requirements,higher requirements have been put forward for the wear resistance,strength and toughness of heavy-haul road rails.In order to better meet the requirements of rails with high wear resistance,Panzhihua Iron and Steel Group has developed high-strength,high wear-resistant U95Cr hypereutectoid rails for trial laying on the Daqin line.The composition of U95Cr rails is different from the previous pearlite heavy rails.The increase in carbon content and the addition of alloying elements have a significant impact on the weldability of the rails.How to obtain stable and reliable welding joint quality for site welding has become a technical problem that restricts the promotion and application of this new rail on the line.YHGQ-1200 gas pressure welding vehicle is the key equipment for railway site welding in China.Therefore,the research on the weldability of 75N U95Cr eutectoid steel rail by using this equipment is of great significance to improve the welding quality of high-strength rail of heavy haul lines.Based on the welding parameters of 75N U78Cr V rail by gas pressure welding,the welding process and post-weld heat treatment process of 75N U95Cr rail were set and optimized in this paper.The joints obtained by setting multiple sets of process parameters are analyzed for the welding thermal cycle process,performance testing,and macro and microstructure observations.The results show that under the optimized process parameters,the joints meet the falling weight test(height 3.8m)for 15continuous joints.The joint impact energy is 6.69J,the tensile strength is 1042MPa,the elongation after fracture is 8.3%,the hardness test result of the rail top surface is395(H_J/H_pis 0.93),and the grain size of the joints in each area is 9.It meets the requirements of TB/T1632"Rail Welding"and"Technical Conditions for Welding High Wear Resistance,High Strength and Toughness Hypereutectoid Rails for Trial Laying Tests".Aiming at the serious softening zone problem of high-strength rail joints,the hardness of the joint softening zone is difficult to stably meet the requirements of H_J1/H_p?0.8 stipulated in the TB/T1632"Rail Welding"standard.To this end,different post-weld normalizing processes(different cooling methods and different air injection parameters)were used to explore the hardness value of softening zone and the width of softening zone.The results show that different cooling methods and different air injection parameters can effectively reduce the width of softening zone(20–50%),due to the increase of cooling rate.The fixed amplitude swing method of air injection is better than the variable amplitude swing method.Increasing the air injection volume can increase the effect of improving the width of softening zone.However,changing the cooling mode and air injection parameters has little effect on improving the hardness of softening zone.