A novel high-efficient welding technology with rotating arc assisted by laser and its application for cryogenic steels

To obtain high efficiency and good weld quality for medium thick steel plates, a novel welding technology of hybrid arc laser welding was proposed through rotating arc assisted by laser. Rotating arc provides heat to melt feeding wire and groove for high deposition and good fusion. Laser is helpful not only to arc rotating, but also to molten pool mixing. The proposed welding technology was used in the application of 9% Ni steel with medium thickness in the field of LNG storage tanks. The 21 mm thick steel plates were successfully achieved with only 2 welding passes. The weld formation was well-qualified, and no defects can be observed. The droplet transfer, keyhole and molten pool flow were investigated with high-speed camera and electric signal analysis. Experimental results showed that the droplet transferred in periodic alternation pattern of rotating spray transfer mode and short-circuit transfer mode. The laser keyhole kept stable during the droplet transfer process. The molten pool was fully mixed under the coupling effect of the arc, droplet and laser beam. The weld metal was in homogenous composition. Low temperature (-196 degrees C) impact energy of weld metal center and fusion line were much higher than related requirements. Obvious dimples on the fracture surface indicated that the fracture mechanism was in ductile fracture mode. Research results provided a theoretical basis for efficient construction and safe service of LNG containers made by cryogenic Ni steel.