Effect of nitrogen and nickel on the microstructure and mechanical properties of plasma welded UNS S32760 super-duplex stainless steels

Super-duplex stainless steels present excellent combination of mechanical and corrosion resistance, due to their strict composition control and ferrite-austenite phase balance. This balance may, however, be disturbed during welding in both the fusion and HAZ due to the rapid cooling rates and may lead to loss of the good corrosion and mechanical properties of the weldments. The present investigation is studying the effect of nitrogen addition in the plasma operation gases and of the increase of nickel in the filler metal, on the microstructure and on the mechanical properties of super-duplex stainless steels welded by the plasma transferred arc (PTA) technique. Results have shown that nitrogen addition in the plasma operation gas affects the mechanical properties of the weldments. It is shown that nitrogen addition in the plasma and protective gas and higher nickel content in the filler metal have both a positive effect on the elongation of the welded specimens and after optimization of the welding parameters very good results may be obtained in terms of tensile strength.