Corrosion resistance of duplex stainless steel weldments in wet CO/sub 2/ and H/sub 2/S environment

The effect of nitrogen to resistance to pitting corrosion and stress corrosion cracking (SCC) in various environments was investigated. The increase in nitrogen content increases these resistances in the base metal, which is due to the improvement in the resistance of γ-phase which has lower chromium and molybdenum contents compared to α-phase. Nitrogen is an essential element to sustain the corrosion resistance of the heat affected zone (HAZ) because it accelerates the formation of γ-phase during cooling and avoids precipitation of chromium carbides or nitrides at grain boundaries. When the nitrogen content is less than 0.08% in 22%Cr, 5.5%Ni 3%Mo base composition the HAZ has little γ-phase to lead to high susceptibility to intergranular corrosion and IGSCC occurs even in pure CO/sub 2/-Cl environment containing no H/sub 2/S. Nitrogen has little effect on precipitation behavior of the base metal by aging heat treatment round 7000C