Defect evolution of 409L stainless steel in high-speed TIG welding

The undercut and humping weld defects in high-speed tungsten inert gas (TIG) welding deteriorate the mechanical properties of the weld, which limit the improvement of modern manufacturing. Based on the heat and mass transfer in the molten pool, the geometry of the molten pool and depression region and the maximum backward velocity of the lateral channel were emphatically analyzed as the heat input being retained to be basically consistent at different welding speeds. As the welding speed increases from 1.0 m/min to 3.0 m/min, the maximum backward velocity of the lateral channel increases from 0.31 m/s to 0.57 m/s, which aggravates the undercut defect. The undercut defect initially appears in the weld at 1.5 m/min and becomes more serious with increasing welding speed. Additionally, the length of the depression region of the molten pool shows an increasing trend. The humping weld defects are first observed in the weld at 2.8 m/min, and the length of the depression region exceeds 3.6 mm. These findings prove the complicated behavior in the molten pool due to the complex thermo-mechanical coupling effect, and also provide a possibility to obtain sound welds efficiently by selecting suitable welding parameters in high-speed TIG welding process.