Effect of laser and laser hybrid welding on the corrosion performance of a lean duplex stainless steel

The use of duplex stainless steel increases steadily worldwide and the fluctuations in nickel price the recent years have contributed to further growth. The lean duplex grade Outokumpu LDX 2101® (EN 1.4162, UNS S32101) has a low nickel content and is alloyed with nitrogen and manganese to give a balanced microstructure. It means that good austenite formation is obtained even when laser welding autogenously (without filler). This is in contrast to most other duplex grades, for which laser welding is normally associated with high ferrite fractions, known to reduce the ductility and corrosion performance. Nd:YAG, CO2 and fiber laser welding of LDX 2101® has been performed with and without filler wire and as laser hybrid welding with gas tungsten arc (GTA) and gas metal arc (GMA). The microstructure was evaluated and related to the corrosion performance, and the mechanical properties are presented. The austenite formation in autogenously laser welded LDX 2101® is not sufficient to completely avoid chromium nitride precipitation and the weld metal pitting resistance is consequently affected. This is particularly seen when fiber laser welding. The mechanical properties of all welds were on a similar level with those of the base metal, while the corrosion performance and ductility were marginally to significantly lower. Use of filler wire when Nd:YAG laser welding and Nd:YAG laser-GTA hybrid welding with and without filler wire, and nitrogen additions to the GTA shielding gas improved the austenite formation and hence the pitting resistance. CO2 laser and CO2 laser-GMA hybrid welding proved to result in most austenite and generally showed the highest pitting resistance of all laser welds.