On the Nitrogen Diffusion in a Duplex Stainless Steel

Duplex Stainless Steels (DSS) have excellent corrosion resistance properties and poor wear resistance. Plasma nitriding is used to increase the surface hardness, by nitrogen diffusion into the crystal lattice, and to improve wear resistance. In this study, DSS samples were plasma nitrided at temperatures between 350 degrees C and 500 degrees C for 240 minutes under an atmosphere of 75% N2 + 25% H2. Aparent diffusion coefficients, activation energy and pre-exponential constant were calculates using the first law of Fick for each material phase, austenite and ferrite. Nitrogen diffusion in both phases appears to be similar. The layer thickness on the alpha phase is greater than in the gama phase. Nevertheless, the difference on the layer thickness in both of the phases is small. From these results, it was proposed a model of nitrogen diffusion into a two-phase stainless steel to explain the morphology of the interface between the layer and the substrate.