Effect of Shielding Gas Composition on Phase Transformation and Mechanism of Pitting Corrosion of Hyper Duplex Stainless Steel Welds

Abstract

The effect of shielding gas composition on the phase transformation and the mechanism of pitting corrosion of hyper duplex stainless steel (HDSS) welds was investigated in highly concentrated chloride environments. The resistance to pitting corrosion of a HDSS tube after welding with Ar shielding gas supplemented with N₂ was increased due to a decrease of the PREN (Pitting Resistance Equivalent Number) difference between the γ-phase and the α-phase in the weld metal and the heat affected zone. Cr nitrides (Cr₂N) were precipitated in the weld metal and the heat affected zone due to a high α-phase content. Cr-depleted zone adjacent to Cr₂N decreased the resistance to pitting corrosion.