Abstract
As a prerequisite for the predictability of properties obtained by a nitriding treatment of iron based workpieces, the relation between the process parameters and the composition and structure of the surface layer produced 111ustbe known. At present, even the description of thermodynamic equilibrium of pure Fe–N phases has not been fully achieved. It is shown that taking into account the ordering of nitrogen in the ε and γ'iron nitride phases leads to an improved understanding of the Fe–N phase diagran1. Although consideration of thermodynamics indicates the state the system strives f01∼ the nitriding result is determined largely by kinetics. Nitriding kinetics are shown to be characterised by localnear equilibria and stationary states at surfaces and intelfaces, and the diffusion coefficient of nitrogen in the various phases, for which new data are presented. The necessary background for process control of gaseous nitriding by monitoring the partial pressure of oxygen in the furnace using a solid state electrolyte is provided.
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