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Therefore, how to improve the comprehensive properties of the LTT welded joints is still in research state so far.Īs a joining technique, tungsten inert gas (TIG) welding, due to its greater requirement to control the welded area, is characterized by its advantage of excellent joining quality. Although LTT weld metals are competent in generating lower RS in welded joints, the toughness of the LTT weld metals is rather low, which limits its application to welding engineering. Using low transformation temperature (LTT) welding fillers, however, numerous studies have demonstrated that the RS state in welded joints can be reversed from tensile to compressive, improving the fatigue strength of welded joints. Tensile residual stress (RS) is known to be detrimental to the fatigue strength of welded joints. The corresponding outcome confirmed that the LTT weld metal using MAG welding was more beneficial to tensile RS reduction. 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. Moreover, the hardness of the LTT weld metal using MAG welding was higher than that of using TIG. Meanwhile, the high angle and coincidence site lattice grain boundaries were dominant in the LTT weld metal using MAG welding. In addition, based on the Taylor factor calculation, the weld metal using MAG welding was more competent in repressing fatigue crack initiation. The LTT weld metal using TIG welding had larger grain size than using MAG. 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 microstructures of the tungsten inert gas (TIG) and metal active gas (MAG) weldings were investigated by using electron-backscattered diffraction and orientation imaging microscopy.
A Cr-Ni type of low transformation temperature (LTT) welding filler was devised in the present study.