Study On New Rail Flash Welding Process And Properties Of Welded Joints

Railway transportation is the backbone of the comprehensive system of modern transportation.It plays a special and important role in the promotion and development of national economy.The seamless track is the symbol of the modernization of track structure.Flash welding plays a dominant role in the rail welding method of seamless track construction.There are great differences between domestic and foreign standards for inspection and construction of rail flash welding type.The main differences are as follows:(1)domestic requirements for normalizing welded joints are not required by most foreign standards;(2)drop weight test is only required in domestic standards;(3)domestic standards for width and uniformity of heat affected zone of welded joints are low.Therefore,exploring the welding technology that meets the requirements of domestic and foreign rail standards,and studying the performance differences and their causes have a very good supporting role for the promotion of China's high-speed rail going out strategy.The paper adopts UN5-150ZB1 mobile on-site flash welder and U75 V hot-rolled steel rails which are widely used at home and abroad for welding test.Through a large number of welding process tests,the rail flash welding process parameters(2# welding process)and conformity are obtained according to Chinese railway standards.Indian Railway RDSO standard rail flash welding process parameters(1# process),and respectively use the welding process parameters and post-weld flame normalizing process combination that meet the above requirements,to obtain three sets of welding test joints :2# process normalizing,2# process non-normalizing,and 1# process non-normalizing.The residual stress,hardness,heat affected zone and other properties of the welded joints are tested and analyzed.To analyze the influence of normalizing and induction heating on the joint performance,the GAAS80/580 welder is used.The process of meeting the requirements of the iron standard,welding the welded joints,obtaining the normalized and non-normalizing welding test joints for relevant tests:(1)The width of HAZ in 2# process non-normalizing welded joints is the narrowest about 78 mm and the widest about 90 mm;the width of HAZ in 2# process normalizing welded joints is the narrowest about 40 mm and the widest about 54 mm;and the width of HAZ in 1# process welded joints is the narrowest about 25 mm and the widest about 30 mm(which conforms to the Indian RDSO standard);(2)The hardness test of the rail top shows that there is almost no softening zone in the 1# process non-normalizing process,and the softening zone after 2# process normalizing is not only wider,but the value of softening point is lower than that before normalizing treatment,through microscopic metallographic structure.Observed that the 2# process precipitates more small pieces of ferrite after normalizing,while the amount of ferrite in the 1# process is relatively small;(3)The X-ray residual stress analyzer based on cos? theory was used to test the top of the five types of welded joints: 2# process normalizing,2# process non-normalizing,and 1# process non-normalizing,GAAS80/580 normalized and non-normalizing.Residual stress of rail waist and rail bottom: The 2# process has residual tensile stress points at the bottom of the rail top rail and the 1# process does not.The 2# process flame normalizing treatment method does not improve the residual stress on the rail surface and is inductively normalized and normalized to the inner part of the rail structure.Improved grain uniformity is useful;(4)Tensile test and impact test results show that the tensile strength and elongation after break of the 1# process non-normalizing are better than those of the 2# process normalizing welded joints,normalizing treatment is beneficial to the improvement of impact toughness,and only normalizing treatment of the three groups of welded joints can meet the requirements of the railway impact performance standard.