Research Of Laser-Mag Hybrid ARC Welding Process On Weathering Resistant Steel SMA490BW

With a booming development of railway transportation in China, high speed and heavy load are the main strategies. To ensure a safe operation of train at a high speed, the research on bogie has been a key issue. Because of a complex service environment and atmospheric corrosion, weather-resistance steel is usually taken as the bogie material. Based on plain carbon steel, elements with good corrosion resistance have been added to SMA490BW weather-resistance steel, such as Cu、P、Cr、Ni,and so on. Metal active gas welding (MAG) is used as the conventional welding method for SMA490BW. But the MAG welding has led to a major welding deformation, a possible flaw of poor fusion, and stress concentration. This paper attempts to start a research of laser-MAG hybrid welding on SMA490BW weather-resistance steel to enhance welding efficiency and solve the problems in MAG welding.The research is based on a comparison between MAG and laser-MAG hybrid welding by performing experiments on SMA490BW weather-resistance steel (sized 12mm) with the method of butt joint welding 30°,40°,60° and angle joint welding 35°,45°,55°, double groove 30-40°, for achieving optimal design of the bogie typical joint groove structure and welding parameters. After gaining different joints in the experiment, test and analysis on structure and mechanical property of joints have been carried out by means of metalloscope, HV hardness tester and electronic universal testing machine, etc. The varying pattern of microstructure and mechanical property with different welding parameters were obtained. Comparative analysis of both welding methods were performed.Compared to the conventional MAG welding joint, the laser-MAG hybrid welding joint showes an obvious goblet shape and has a deeper welding penetration. Hybrid welding can use smaller groove, larger size of a blunt edge, which can effectively reduce the number of welding layers and the heat input general. Welding deformation and residual stress test show that the hybrid welding can reduce welding deformation and the residual stress of the welding joints. It can also ensure the assembly accuracy of later period, and improve the safety and reliability of the steering frame. At the same time, compared to MAG welding, the hybrid welding can improve the welding efficiency.Microstructure tests show that the microstructure of hybrid welding and MAG welding joint were similar. Certain differences were found in the grain size, and microstructure of hybrid welding were more fine. The hardness value in overheated zone was high, and the hardness of base material was low, heat affected zone of hybrid welding was narrower than that of MAG welding.In the tensile test, all of the fractures occurred in the base metal. Tensile strength values can meet the standard. The tensile strength of the hybrid welding joint can increase by 5MPa compared to the MAG welding joint. Bending test results show that the bending resistance ability of laser-MAG hybrid welding is better than that of conventional MAG welding joints. Curved micro crack was not appeared in low temperature impact test. The impact toughness of heat affected zone was best, and the impact toughness of the weld zone was lower than the parent material. The impact power of hybrid welding can increase by 23J than that of the MAG welding, the impact power of heat effect area in hybrid welding is increased by 9J than that of MAG welding. Therefore, the laser-MAG arc welding has the ability to achieve the optimization and upgrading of bogie typical welded joints, with the feasibility of application of engineering.