Effect of the H2 content in shielding gas on the microstructure and oxidation resistance of Fe-15.7 wt.% Cr-8.5 wt.% Mn steel GTA welds

The mixing of hydrogen in Ar-N-2 shielding gas could produce a Fe-15.7 wt.% Cr-8.5 wt.% Mn steel weld bead shape in accordance with ISO 5817 quality level B at the welding speed of 5.4 nun s(-1). At this speed the acceptable weld bead shape could not be obtained when using Ar-N-2 as the shielding gas. The beneficial role of hydrogen could improve the welding productivity. At the same welding speed, the addition of hydrogen in the Ar-N-2 shielding gas reduced the concentration of nitrogen dissolved in the weld, thus reducing the austenite stabilising effect due to nitrogen and increasing the delta ferrite content in the weld. Mixing hydrogen in the Ar-N-2 shielding gas considerably reduced the weld oxidation rate, possibly from the hydrogen dissolved in the oxide.