Study on Molten Pool Flow and Porosity Defects in Laser–Tungsten Inert Gas (TIG) Welding of 4J36 Invar Steel

The Invar steel molten pool is characterized by low fluidity of the molten pool due to high tension, which hinders the escape of gases and exacerbates the formation of porosity defects. In this study, the influences of different welding process parameters, material properties, and U-groove on the flow behavior of the molten pool of laser-tungsten inert gas (TIG) hybrid welding of Invar steel are investigated by numerical simulation and high-speed photography. This research proposes effective measures to suppress porosity defects, such as optimizing process parameters and extending the existence time of the molten pool. In conclusion, this study systematically investigates the dynamic mechanism of the formation of welding defects in 4J36 Invar steel and provides important theoretical support for the optimization of the welding process of 4J36 Invar steel. The results indicate that controlling the laser power at 4-6 kW, welding speed at 0.5-1.0 m/min, and welding current at 150-170 A can stabilize the molten pool flow and keyhole and promote the molten pool flow and gas escape.