In order to develop a new W-containing duplex stainless steel based on the composition of Fe-22Cr-5.5Ni-0.15N, molybdenum in Fe-22Cr-5.5Ni-0.15N alloys is totally or partially substituted by tungsten and the effects of tungsten addition on the localized and stress corrosion of these alloys have been investigated through the potentiodynamic polarization test and constant extension rate test in chloride solution.
With increasing W content, ferrite content in Fe-22Cr-5.5Ni-0.15N-x W alloy is significantly increased. Pitting potential for these alloys, measured potentiodynamically in a deaerated 3.5% NaCl solution, increases linearly with W content from 125mV, SCE for W-free alloy to 430mV, SCE for alloy containing 11%W, showing enhancing effect of W on the resistance to localized corrosion of duplex stainless steel. Specifically, it has been demonstrated that, at equivalent atomic percent, W has a similiar enhancing effect on the resistance to localized corrosion as does Mo. Among Fe-22Cr-5.5Ni-3Mo, Fe-22Cr-5.5Ni-W, and Fe-22Cr-5.5Ni-3W-1Mo alloys, the Fe-22Cr-5.5Ni-3W-1Mo alloy has shown the best resistance to stress corrosion in boiling 40% $MgCl_2$ solution of Mo in Fe-22Cr-5.5Ni-3Mo-0.15N alloy by W has a beneficial effect on reducing embrittlement induced by precipitation of σ phase, Showing that W significantly suppresses the precipitation of σ phase. In conclusion, Fe-22Cr-5.5Ni-3Mo alloy, a commercial alloy, can be best replaced by a new W-containing duplex alloy of Fe-22Cr-5.5Ni-3W-1Mo.
