Study On Microstructures And Mechanical Properties Of The Welded Joints Of Bogie Frame Material In Carriage

High speed of locomotive is becoming a strategic direction of the development of railway transportation in China. Higher materials quality and higher performances of the corresponding welded joints of bogie frame are desired to fit for the more complicated loads resulted from the constant heightening of running speed. Therefore, selecting suitable frame materials and upgrading the welding quality can be of great application value and practical significance for the safe operation of high velocity train.In this paper, by using JM-56 solid welding wire and mixed gas arc welding method 16MnR,S355,S275 and 16MnR&Q235B cast steel were welded under same processing parameters. Then, tensile, impact, microhardness and fatigue tests on the corresponding welded joints were carried out, and the microstructures and fracture morphologies were observed as well.The results showed that 16MnR,S355,S275 and 16MnR&Q235B cast steel when welded by using welding wire of JM-56 under the technological conditions of this study, the microstructure in welded metal mainly contains block and strip proeutectoid ferrites that appeared along the columnar grain boundaries, a little pearlites and granular bainites, while tenuous acicular ferrites appeared mainly within the grains. But in the welded metal of S355 and S275, a certain amount of Widmanstatten structures were observed.Fusion area and overheated zone mainly contains block or columnar proeutectoid ferrites, a little pearlites, granular bainites and some ferrite banding generated from grain boundaries to inside of grains. Meanwhile, a little acicular ferrites appeared within the welded joint, Nevertheless, in fusion area and overheated zone of 16MnR&Q235B also contains a quantity of Widmanst?tten structures.Welded by using JM-56 solid welding wire under the same technological conditions in this study, the low-temperature impact toughness of 16MnR is good at both -20℃and -40℃; Comparing with their base metal, impact toughness of welded joint of S355 and S275 steel has dramatic declined; however, the low-temperature impact toughness of 16MnR&Q235B cast steel is excellent at both -20℃and -40℃. The impact toughness of four different kinds of welded joints studied in this paper are all higher than the requirement of bogie frame at both -20℃and -40℃. The fatigue limit of 16MnR,S355 and 16MnR&Q235B welded joints are 223.5 MPa,283.9 MPa,220.5MPa respectively when the life period assigned as 5×106 circulations.