Influence of ultrafine-grained structure of martensitic and austenitic steels on diffusion processes at low-temperature ion nitriding

The effect of ultrafine-grained (UFG) structure in martensitic and austenitic steels on diffusion processes at low-temperature ion nitriding was investigated. UFG structure of steels was obtained by intensive plastic deformation by high pressure torsion (HPT). The low-temperature ion nitriding was carried out at a temperature of 450°C for 4 hours. Results of optical microscopy and microhardness measurements of samples before and after ion nitriding were studied. The UFG structure of martensitic and austenitic steels allow to increase a thickness of nitriding layer up to 2 times compare with coarse-grained structure. The nitriding layer of the UFG and coarse-grained steels was composed of α-phase contained nitrogen. The microhardness measurements of nitriding layer were shown that values for the martensitic and austenitic steels with UFG structure are more 1.25 times than the steel with coarse-grained structure.