Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N₂-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N₂-shielded welding followed by N₂-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N₂-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N₂-shielding. The amount of nitrides was lower in N₂-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N₂-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds.

避免低奥氏体含量和形成氮化物是双相不锈钢（DSS）激光焊接的主要挑战。本研究旨在研究在不牺牲生产率的前提下，在自发激光焊接DSS的过程中促进奥氏体形成的有效方法。在这项研究中，研究了保护气体和激光再加热对1.5毫米厚的FDX 27（UNS S82031）DSS焊接的影响。研究了四个条件：氩气保护焊，N ₂保护焊，Ar保护焊和Ar保护激光再加热以及N ₂保护焊和N ₂屏蔽的激光加热。进行了光学显微镜，热力学计算和Gleeble热处理，以研究微观结构和化学成分的演变。对于氩保护焊，奥氏体分数为22％，对于N ₂保护焊，奥氏体分数为39％。有趣的是，激光再加热并没有显着影响用于Ar屏蔽的奥氏体分数，而对于N ₂屏蔽，奥氏体分数增加到57％。N _2中的氮化物含量较低屏蔽样品与Ar屏蔽样品相比。在热影响区也观察到了相同的趋势。根据计算的平衡相图和在1100°C进行的Gleeble平衡热处理后的奥氏体分数评估，焊缝金属的氮含量对于N ₂保护焊缝为0.16％，对于Ar保护焊缝为0.11％，证实了氮对促进焊缝的重要性焊接特别是再加热过程中的奥氏体形成。最后，建议结合使用纯氮气作为保护气体和激光再加热道次的焊接可以显着改善DSS激光焊缝中的奥氏体形成并减少氮化物形成。