SIMULATION OF THE RESIDUAL-STRESS DEVELOPMENT IN THE DIFFUSION LAYER OF LOW-ALLOY PLASMA-NITRIDED STEELS

A computer program has been developed to simulate the changes of resid ual macro stress during plasma nitriding as a function of time and dis tance from the material surface. This program is based on a model whic h considers the superposition of the several contributions to stress. The only inputs required are the plasma nitriding and substrate materi al parameters. The variables are the change of nitrogen concentration in solution in the substrate matrix, the volume misfit between The mat rix and the increasing volume fraction of nitrides, the dissolution of carbides during the nitriding process in addition to the relaxation o f stress at the nitriding temperature and the thermal stresses. A comp arison shows that the simulated residual stress profiles are very simi lar to those measured by the X-ray diffraction technique for short and Ion:: nitriding times at different temperatures.