Microstructure and corrosion resistance of super duplex stainless steel 2507 joint by laser beam welding with argon-nitrogen mixed shielding gas

• Using argon-nitrogen mixed shielding gas in laser beam welding of SDSS 2507 effectively increases weld seam austenite content by 10.7 % compared to pure argon shielding. • Weld seam austenite primarily exists as grain boundary and intragranular forms, with no significant Widmanstätten austenite due to rapid cooling rates, and its orientation remains unaffected by nitrogen in the shielding gas. • Compared with Ar-shielded welds, the total nitrogen content in Ar-N 2 mixed shielded LBW welds increased by 0.012 wt%, while the nitrogen content in the austenite phase decreased. • Higher ferrite content and significant PREN differences between austenite and ferrite phases may be the reason for decreased pitting corrosion resistance. This study addresses the urgent need for quantitative investigation of nitrogen content, microstructure, and corrosion resistance in laser beam welded SDSS 2507 joints to understand the welding process’s intrinsic nature and enhance joint performance. Comparative experiments were conducted using pure Ar shielding (control) and 75 % Ar + 25 % N 2 (experimental), with a laser power of 1.8 kW and welding speed of 0.015 m/s. Results show that Ar-N 2 shielding increases weld seam austenite content by 10.7 % (from 19.2 % to 29.9 %), primarily as grain boundary and intragranular austenite, with no Widmanstätten austenite due to rapid cooling. Compared with Ar-shielded welds, the total nitrogen content in Ar-N 2 mixed shielded LBW welds increased by 0.012 wt%, while the nitrogen content in the austenite phase decreased. Ferrite texture strengthens significantly in welds (maximum strength 13.35 vs. 4.25 in base metal), aligning with base metal rolling direction, while austenite orientation remains unaffected. Pitting corrosion resistance of both welds is comparable and inferior to the base metal, attributed to higher ferrite content and PREN disparities between phases.