The influence of tungsten (W) on properties in high nitrogen stainless steels

Superaustenitic stainless steels with about 6% molybdenum (Mo) have now been used successfully for over twenty years because of their high corrosion resistance. Requirements for even better performance have resulted in more highly alloyed superaustenitic steels, also with high nitrogen (N) levers. Substituting W for Mo in stainless steels has been claimed to have both negative and positive effects. To investigate these effects, especially on corrosion resistance in high Mo superaustenitic stainless steels, a series of eight experimental steels was produced. The heats were designed to investigate the effects of substitution of W for Mo in a base alloy containing 24% chromium (Cr), 22% nickel (Ni) and 0.5% nitrogen (N). To achieve this Mo and W were varied between 5 to 7% and 0 to 5% respectively The microstructures and resistance to localised corrosion were investigated for solution annealed and sensitised samples. Addition of W improved the resistance towards localised corrosion in a similar way as Mo. However, the structural stability was decreased on replacing Mo by W. This negative effect was observed in the whole temperature range studied and had also a negative influence on the crevice corrosion resistance.