Nitriding of a martensitic Cr-steel. Microstructure and nitrogen diffusion

Synthetic FeCrC steels were prepared from purified electrolytic iron. These alloys were used to study nitriding of tool steels. As-quenched and tempered martensitic samples were nitrided in gaseous phase. The microstructures after nitriding were studied at various scales (SEM and TEM) and the various types of precipitates were classified according to their size, The depths of nitriding were determined using chemical attack, microhardness and Luminous Discharge Spectrometry (LDS). The LDS measurements made it possible to determine the profile of nitrogen concentration in the whale nitrided layer. Two models of nitrogen diffusion (with and without precipitation depending on the nitrogen content) are necessary for describing the experimental concentration curves. The values of D calculated in the two models are in good agreement.