Nitriding of steel powder-thermodynamic calculations and experiments

Thermodynamic calculations have proved to be a powerful tool in the development of alloys. By coupling thermochemical and phase diagram information using models describing the Gibbs energy of the various phases in a system, by the so-called CALPHAD method, it is possible to predict phase equilibria in multicomponent alloys with reasonable accuracy. In the present work it is shown how thermodynamic calculations have been applied to problems concerned with nitriding of steel powder. Of interest is the solubility of N in solid phases in equilibrium with N containing gases and the stability and composition of various nitrides and carbonitrides. Using available databases with, in some cases, some additions; calculations have been performed to plan experiments and to understand experimental results. In addition, experiments have been performed to adjust thermodynamic parameters. Examples are given from experiments with stainless steels and tool steels. Nitriding experiments, sintering studies and long-term heat treatments for studying equilibrium compositions of carbonitrides are presented. Experimental and calculated results are compared. (orig.)