Comparison of Microstructure and Residual Stress Between TIG and MAG Welding Using Low Transformation Temperature Welding Filler

A Cr-Ni type of low transformation temperature（LTT）welding filler was devised in the present study.The LTT weld microstructures of the tungsten inert gas（TIG）and metal active gas（MAG）weldings were investigated by using electron-backscattered diffraction and orientation imaging microscopy.The results showed that the LTT weld microstructures prepared by TIG and MAG weldings were primarily martensite with 17.5% and 8.0% retained austenite,respectively.The LTT weld metal using TIG welding had larger grain size than using MAG.In addition,based on the Taylor factor calculation,the weld metal using MAG welding was more competent in repressing fatigue crack initiation.Meanwhile,the high angle and coincidence site lattice grain boundaries were dominant in the LTT weld metal using MAG welding.Moreover,the hardness of the LTT weld metal using MAG welding was higher than that of using TIG.Based on heat input and phase transformation,finite element method was applied to analyzing the tensile residual stress（RS）reduction in welded joints prepared by both conventional and LTT welding fillers,respectively.The corresponding outcome confirmed that the LTT weld metal using MAG welding was more beneficial to tensile RS reduction.