The mathematical model of iron nitriding described here considers the kinetics of the chemical reaction at the metal atmosphere interface as well as the diffusion processes occuring inside the metal phase. The chemical composition of the diffusion layer has been determined by the thermodynamical analysis of the chemical reactions taking place between iron and the nitriding atmosphere and by examining the equilibrium state of the Fe-N system. The calculations assume that the flux of nitrogen atoms from the nitriding atmosphere to the steel is proportional to the difference between the equilibrium and the actual nitrogen concentrations at the steel surface. Since carbon affects the interphase equilibrium of the Fe-N system, one can use the model implemented here for predicting the effects of nitriding of steels with low carbon concentration. The model assumes that the kinetics of the reactions taking place across the interphase boundaries in the solid phase is driven by the diffusion process, hence the boundary location can be determined from the differences between nitrogen fluxes across various interphase boundaries.
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