Research On The Optimization Of Heat Treatment Technology And Properties Of Rail Continuous Flash Welding Joint

With the development of the railway，more requirements were put forward onwelded joints which are as the connecting parts of the CWR(Continuous WeldedRail). Considering the problems happened in the joints, it is necessary to study onthis issue.In response to these problems, the U71Mn and U75V rail welded joints suppliedby Chengdu Shibantan Rail welding plant are applied as sample in the currentresearch. Not only the performance and organizational changes in the different post-weld heat treatment are studied, this article also discuss emergence reason of themartensite and the ways to eliminate it.The main results are as follows:We defined the composition of sample steel by the method of Chemical analysis,through the Gleeble-1500D thermal simulated test machine, phase transitiontemperature in different heating rates of two rails was measured. Joints underdifferent heat treatment processes show different performance, we discussed thechange rule of joint and parent material performance by Charpy impact test at roomtemperature. With the aid of metallographic microscope, the microstructure wasobserved and the grain size was measured, in the mean time we analyzed the reasonsthat cause the difference of the impact toughness of U71Mn and U75V rail weldedjoints in the same heat treatment. The scanning electron microscope analysis showedthat reasonable heat treatment process could make the fracture showed goodtoughness characteristics. Using microhardness tester, we also got the Hardnessunder different heating temperature and cooling rate.Without post-weld heat treatment, the emergence of martensite in the weldedjoints is a common phenomenon. We chose the joint which this problem was mostserious as sample in the next research. EDS (Energy Dispersion Spectrum) analysisshowed that the cause of martensite appeared in the welded joints, especially inU71Mn welded joints, was mainly due to segregation of Mn and C. The heattreatment of joints could effectively reduce the segregation status of the C element,but it worked little to the Mn element.The above analysis shows that the main strengthening mechanisms of thewelded joints is the fine grain strengthening and improvement of mechanical properties of pearlite. Reducing the Mn content in the rail is an effective way toreduce the occurrence probability of martensite in welded joints.