Effect of nitrogen addition on the microstructure and mechanical behavior of 317L and 904L austenitic stainless steel welds

A systematic study of the effect of nitrogen addition on the microstructure and mechanical behavior of two different austenitic stainless steel welds, namely, 317L and 904L was carried out. For this, nitrogen content of the welds was altered by introducing different proportions of nitrogen gas into the argon shielding gas during welding. Nitrogen addition to 317L weld changed solidification mode from primary ferrite to primary austenite. As 904L weld solidify by primary austenitic mode, no change in the solidification mode was found with N addition. The results showed that, with rise in nitrogen content of the welds, various mechanical properties like ultimate tensile strength and ductility had improved significantly and that the welds prepared with 1 vol% N₂ in the shielding gas indeed failed in the base alloy making the weld stronger than the parent metal. It was noticed that the effect of N towards improving the mechanical properties 904L weld was higher than that found in the case of 317L weld.