HENRY GRANJON PRIZE COMPETITION 2009 Winner Category B: "Materials Behaviour and Weldability" PITTING CORROSION RESISTANCE OF GTA WELDED LEAN DUPLEX STAINLESS STEEL

The use of lean duplex stainless steel increases steadily worldwide and the fluctuations in nickel price in recent years have contributed to further growth. The weldability of these grades is different from that of the substituted austenitic grades and this paper focuses on the effect of weld metal microstructure and weld oxide on the pitting corrosion resistance. The influence of chromium nitride precipitates on the corrosion performance is illustrated and it is shown that if the weld metal has sufficient nitrogen content and hence adequate austenite formation, the weld oxide controls the location of pitting. Diffusion and oxidation are normally the discussed processes affecting the composition and distribution of the heat tint, but here a new approach to weld oxide formation is proposed. It is shown that manganese is evaporated from the weld metal and contributes to forming thicker weld oxide by subsequent deposition. Addition of nitrogen to the shielding gas further enhanced the manganese evaporation and also formed a significant fraction of oxynitrides in the weld oxide.