This investigation has shown that a low alloyed duplex stainless steel is best GMA welded with a shielding gas consisting of 2% carbondioxide (CO₂), 30% helium (He) and 0.03% nitric oxide (NO) in argon (Ar). This shielding gas is also very suitable for austenitic grades like 304 or 316. A high alloyed super duplex stainless steel is however best GMA welded with an almost inert shielding gas consisting of 0.03% NO in argon.