Research On Full Penetration Welding Process,Microstructure And Properties By High Frequency Pulse MAG Welding Of S355J2W+N Weather-resistant Steel T-joint

S355J2W+N weather-resistant steel,also known as atmospheric corrosion resistant steel,has good weldability,economy and comprehensive mechanical properties,and is widely used in high-speed train bogie frames.The joint form of the bogie frame is mostly T-shaped fillet(HV weld).In the actual welding production process,it is mostly conventional pulse MAG welding.Due to the lack of space accessibility,the welding gun is not easy to reach the root of the weld.The root weld is prone to insufficient fusion.To solve this problem,the method of increasing the welding heat input is often used to increase the root penetration,but it also leads to an increase in welding residual stress.This test uses high-frequency pulse MAG welding for welding test.The pulse frequency is higher,and the arc shape is easier to quickly reach the "pyramidal".The area of the arc on the molten pool is larger,and the penetration of the sidewall is increased.Solve the problem of poor root melting in the actual production of bogie frame welding,and reduce welding residual stress.This test uses high-frequency pulse MAG welding and conventional pulse MAG welding to perform T-groove(HV weld)and non-groove T-joint welding process tests on 12 mm medium-thick plate S355J2W+N weather-resistant steel,measure its welding Research and analysis of the temperature field of thermal cycling joint,welding residual stress of T-joint without groove,welding joint microstructure,weld Vickers hardness and weld structure EDS,XRD,EBSD.The specific research results are as follows:Under the same working conditions,the welding temperature of the characteristic area(2mm from the welding toe)of conventional pulse MAG welding is higher than that of high-frequency pulse MAG welding,compared with conventional pulse MAG welding,the residual stress of high-frequency pulse MAG welding is lower,More acicular ferrite was observed in the weld structure,and no side slab ferrite formation was observed;the hardness of the welded joint under the two welding methods was lower than 380HV10,which met the requirements of welding procedure qualification,and The maximum hardness of each working condition falls in the overheated zone;the residual stress of conventional pulsed MAG welding is higher than that of high-frequency pulsed MAG,the element composition of the weld structure is similar to that of the welding wire,and no element segregation occurs due to the influence of the welding process,The phase of the weld is mainly bcc ferrite,and no fcc ferrite is observed,the EBSD grain orientation difference distribution map infers the content of acicular ferrite in the 30 o,55o groove angle of the high-frequency pulse MAG welding They are 51.4% and 52.9% respectively,and the acicular ferrite content of 55 o bevel in conventional pulse MAG welding is 23.3%.