Effect of nitrogen addition on corrosion resistance of 1.5Si-19Cr-5Ni-2.7Mo duplex stainless steel

In order to improve the corrosion resistance of ASTM A 669 the effect of nitrogen addition of about 0.1 mass% was studied. The resistances of base metal and welded joints of steels with and without nitrogen to crevice corrosion and stress corrosion cracking in chloride environments were evaluated in comparison to SUS 304 and 316 L as reference materials. The effects of nitrogen addition, restraint stress and filler metal on microstructure, especially formation of austenite phase in the welding heat affected zone were also investigated. The addition of nitrogen improved the corrosion resistance and accelerated the precipitation of austenite phase in the heat affected zone. Although an austenite free zone which might cause intergranular attack tended to form in the heat affected zone by welding under restraint stress, the selection of proper filler wires such as 0.01C-23CR-7Ni-3Mo-0.14 N steel made it possible to produce a sound joint with adequate austenite phase to prevent intergranular attack.