Study On Welding Process And Metallurgical Behavior Of Gas Metal Arc Welding With Flux Cored Wire Of HSLA Steel For Bogie

Bogie,as an important part of high-speed train,the welding of its steel structure mainly used gas metal arc welding,there are problems such as low welding efficiency,big welding splash.As a new type of welding material which has been developed in the world in recent years,metal cored wire has the characteristics of fast deposition efficiency of solid wire and convenient adjustment of metallurgical composition of flux cored wire.It has great application prospect for the welding structure of high-speed train bogie.In this paper,pulsed MAG welding process test of Q345E steel of 12mm thickness was carried out with three kinds of welding materials,and the welding seam forming rules of different welding materials under different welding parameters were studied by bead-on-plate welding.The metal transfer mode,arc and splash characteristics of different welding materials under different electric parameters were studied by high speed camera image acquisition system.The metallographic structure of different welding materials and mechanical properties of joints were analyzed.The plasma temperature in the droplet reaction zone was obtained by spectral analysis.The theoretical calculation and analysis of the process of adding and removing oxygen in the droplet reaction zone and the pool reaction zone of the flux-cored wire are carried out.The results show that the weld penetration and weld width using three welding materials change with the welding current and welding speed.As a result of the welding metallurgical reaction of its core composition?SiO₂,TiO₂?,the content of oxygen in the droplet and the pool increases,the surface tension of liquid metal/slag decreases,and the pool flows more easily from the center to the periphery,forming a wide and shallow weld appearance.The butt welding experiment shows that the welding efficiency of HSLA steel can be increased by 20%by using metal cored wire.The research on the metal transfer behavior of three kinds of welding materials shows that the droplet transition mode is basically short circuit transition and big droplet repulsion transition,and the welding splash is large.With the increase of current value,the metal transfer mode is basically changed into the droplet transition mode.The droplet transition of flux cored wire with high current coexists with droplet transition and granular transition.The semi-molten slag column between the wire tip and the pool can promote the droplet transfer to the pool and reduce the spatter.The results show that the tensile strength of the weld metal of different welding materials is higher than that of the base metal,and the tensile samples are all broken at the base metal.Weld metals using solid wire and metal cored wire are strengthened by solid solution strengthening of alloying elements,so that their tensile strength is similar.However,due to the relatively high Ni content of metal cored wire,its low temperature impact toughness is higher than that of solid wire.Because of filling layer of metal in the process of recrystallization Mn expand the austenitic phase,strong carbide forming elements such as Ti,Nb,V inhibition of grain growth,organization,lateral proeutectoid ferrite and lath ferrite amount,through the combination of fine grain strengthening,solid solution strengthening,weld strength toughness is better than the other two kinds of welding materials.Microhardness test shows that GMAW and FCAW have relatively larger heat input,larger hardness in coarse crystal zone of cover layer,tempering in heat affected zone of filler layer and bottom layer,microstructure changes into fine ferrite,and hardness is close to that of welding seam.Boltzmann plot method was used to calculate the plasma temperature in the central region of the arc at 8309K.The oxygenation kinetics in the droplet reaction zone of flux cored wires was analyzed.It is deduced from the theory that the oxidation reaction at the interface of slag gold is stable in the non-equilibrium state,and there will be no mutation in the non-equilibrium state due to some disturbance.