Numerical Modelling of Mechanical Anisotropy during Low Temperature Nitriding of Stainless Steel

A 3D Finite Element method (FEM) model for investigation of the anisotropic mechanical behaviour of austenitic stainless steel during nitriding is presented. The model considers the non-linear concentration dependent diffusion of nitrogen including trapping by chromium, the surface reaction, elastic and plastic anisotropy and influences on thermodynamics (solubility) and diffusion kinetics. Large differences in the nitrided case thickness have previously been attributed to the elastic and plastic anisotropy, which in turn affects the diffusion and solubility properties of nitrogen. The two mechanically distinctive grain orientations <001> and <111> are simulated and the stress, strain and concentration profiles are discussed and compared to experimental findings.