Microstructure and corrosion resistance of laser welded joints of high-nitrogen steel

With the development of high-nitrogen steel in the field of marine engineering, the performance requirements for its welded joints are becoming increasingly stringent. To investigate the microstructure, elemental changes, and corrosion resistance of the welded joints under different laser powers, high-nitrogen austenitic stainless steel with a nitrogen content of 0.7% was welded by a semiconductor laser. The results indicate that as the laser power increases, the penetration depth and width of the weld increase; the dendritic structures in the weld increase, and the nitrogen content at the weld decreases, forming compounds such as carbides and nitrides. At a laser power of 2 300 W, the bending strength of the joint reaches a maximum of 4 346.5 N, accounting for approximately 92.7% of that of the base metal. The hardness of the joint is lower than that of the base metal, and there is little difference under different laser powers. Electrochemical corrosion tests reveal that at a laser power of 1 900 W, the nitrogen loss is minimal, which is more conducive to the formation of a passivation film; the capacitive arc radius is the largest, and the corrosion current is the smallest, resulting in better pitting corrosion resistance of the welded joint.