Welding porosity and nitrogen content are considered significant factors affecting the mechanical properties of fusion-welding joints of high-nitrogen steel. In this study, a method of applying mechanical vibration in the welding process to reduce weld porosity and increase weld nitrogen content was investigated. The effects of mechanical vibration on porosity, tensile, and impact properties were analysed. The results indicated that the bubble floating speed in the vibrating weld pool is faster than that in the general welding mode. With the increase of mechanical vibration frequency, the porosity of the weld decreased at first and then rose. The tensile strength and impact energy increased first and then decreased, and the fracture surface indicated a ductile fracture.

This paper deals with laser-arc hybrid welding of high nitrogen stainless steel (HNS) with 1.2 mm diameter of austenitic stainless steel (ASS) filler wire. The welding was carried out with different shielding gas mixtures like 100%Ar, 95%Ar+5%N2, 90%Ar+10%N2, 94%Ar+5%N2+1%O2 and 89%Ar+10%N2+1%O2. The effects of shielding gas composition on the welding stability, microstructure and mechanical properties were analyzed. The results show that the weld seam forming and welding stability are improved when 1%O2 is added to the mixture of Ar+N2, and the nitrogen content in the weld increases significantly. The pore ratio is the lowest in 90%Ar+10%N2 shielded weld, when 1%O2 is added to 90%Ar+10%N2, the pore ratio increases slightly. The ferrite percentage is the lowest in 89%Ar+10%N2+1%O2 shielded weld. The 89%Ar+10%N2+1%O2 shielded welded joints feature better mechanical properties.

To address the challenge of porosity suppression in laser-arc hybrid welding of high-nitrogen steel, a weakly coupled laser-arc welding method suitable for high-nitrogen steel is proposed. A test platform for composite and “sandwich” welding of high-nitrogen steel was constructed, and this weakly coupled laser-arc welding method was thoroughly analyzed in terms of droplet transfer, arc morphology, keyhole stability, electrical signal stability, weld formation, and porosity rate. The research results show that when the distance between the laser and arc is 6 mm, the droplet transfer mode is jetting, fine droplet, or mixed, with stable, uniform transfer, a stable keyhole, minimal electrical signal fluctuations, and good weld formation quality. The arc is elongated due to laser attraction, increasing the molten pool area and reducing its solidification rate, which provides sufficient time for bubbles to escape, resulting in a pore-free weld. This proves the effectiveness of the weakly coupled laser-arc welding method for high-nitrogen steel, achieving a high-quality, pore-free weld with excellent formation quality. These findings provide guidance and reference for composite welding processes of high-nitrogen steel.