Thermodynamic study on welding wire design of high nitrogen austenitic stainless steel

Based on thermodynamic calculations, the effect of pressure and alloying elements on the nitrogen content, solidification mode, and welding characteristics were investigated in this study. By increasing the partial pressure of N2, the nitrogen content in the weld pool increased dramatically, and the γ zone was enlarged. The nitrogen content increased as alloying elements such as Cr and Mn were added to the molten steel. The δ zone with high temperature treatment was compressed by adding Ni. These alloying elements play important roles in the formation of the single γ region at the temperature of 298 K. With proper Mn addition, the phase area of γ was extended and became more stable, and the “ferrite trap” was also avoided. Two kinds of welding wires with different nitrogen contents were developed and corresponding MIG welding experiments were performed. As the nitrogen content in wire was higher than that in the base metal, severe blowhole defects and mixture microstructure of δ and γ developed.