Structure of the superficial region and mechanical properties of nitrided cast steels

A series of cast steels were subjected to two-stage low-temperature nitriding. Mossbauer, XRD and mechanical investigations were carried out for both as-cast and nitriding materials in order to determine phase composition (especially the content of gamma'-Fe4N and epsilon-Fe2-3N), microhardness of the superficial region as well as tribological properties. It has been stated that the relative content of iron-nitrogen phases strongly depends on chemical composition of the cast steel and the effective thickness of the surface layer comprising iron nitrides is less than 0.015 mm. Considerable increase of surface microhardness and wear resistance of nitrided specimens in comparison with their as-cast counterparts has been observed. It has been found that the values of microhardness of nitrided samples at the surface are above twice larger than those in the core.