Abstract
The microstructures and corrosion properties of ferritic and austenitic stainless steels have been investigated after plasma and gas nitriding at 200-450° C. Little difference was observed between the surface layers produced by the two nitriding techniques: that on ferritic X6Cr17 consisted of ferrite plus epsilon-carbide, that on the austenitic X5CrNi18-10 was the expanded austenite S phase. Pitting resistance of X5CrNi18-10 was improved by nitriding at up to 420° C, but deteriorated for higher nitriding temperatures. The presence of epsilon-carbides in the layer on X6Cr17 slightly reduced pitting resistance for nitriding temperatures up to 440° C. Annealing the nitrided specimens degraded corrosion resistance by redistributing the nitrogen in the surface layer and promoting chromium nitride precipitation.