Stress induced nitrogen diffusion during nitriding of austenitic stainless steel

The nitrogen distribution in plasma nitrided austenitic stainless steel at moderate temperatures is explained by non-Fickian diffusion model. The model involves diffusion of nitrogen induced by internal stresses created during nitriding process. For mathematical description of stress induced diffusion process the equation of barodiffusion is used which involves concentration dependent barodiffusion coefficient. For calculation of stress gradient it is assumed that stress depth profile linearly relates with nitrogen concentration depth profile. The fitting is done using experimental curves of nitrogen depth profiles for 1Cr18Ni9Ti nitrided austenitic stainless steel at two different nitrogen fluxes. Fitting is in good agreement in both cases. The diffusion coefficient D = 1.68 × 10−12 cm2 s−1 at nitriding temperature 380 °C was found from fitting.