The effects of nitrogen flow rate and shielding gas type on the microstructure and properties of laser welded high nitrogen austenitic stainless steel joint

Abstract

High nitrogen austenitic stainless steel exhibits excellent mechanical properties and corrosion resistance. However, nitrogen loss during welding significantly impacts the performance of the welded joints. This study systematically investigates the effects of nitrogen flow rate and shielding gas type on the microstructure, mechanical properties, and corrosion resistance of laser welded high nitrogen austenitic stainless steel joint. The results indicate that, when nitrogen is used as the shielding gas, increasing the gas flow rate decreases the average ferrite phase content of weld metal (WM) from 2.0 % to 0.8 %, while the nitrogen content increases from 0.38 % to 0.45 %, the increase of nitrogen atmosphere concentration and partial pressure above the molten pool is the main reason for the increase of nitrogen content in the WM. But the tensile strength is not much different, both are about 1290 MPa and the fracture position is in the WM. When argon is used as the shielding gas, the ferrite content of the WM increases to 2.2 %, and the tensile strength of the joint decreases to 1135 MPa. When the nitrogen flow rate is 35L/min, the corrosion rate of the WM is 0.0925mm/a, while the corrosion rate is 0.1052mm/a under argon protection, which is 17.67 % higher than that of the base metal (BM). The reduction of the Cr-depleted zone and the corrosion inhibition of N element with increased nitrogen flow rate are the primary factor contributing to the improved corrosion resistance of the WM.