Abstract
The paper presents research results on the influence of martensitic steel ultrafine-grained (UFG) structure on diffusion processes at low-temperature ion nitriding. UFG structure was obtained through severe plastic deformation by torsion (SPDT) of coarse-grained (CG) steel samples. Ion nitriding was performed under the constant voltage mode during 4 hours at a temperature of 420 °C. Optical microscope was used to study the microstructure of a sample. Thickness of a modified layer was defined according to measurements of microhardness by depth. The analysis of research results showed that UFG steel structure enhances effective intensification of diffusion processes by 1.7 times, which in its turn contributes to low-temperature modification of a surface. At the same time, surface microhardness of UFG steel after treatment amounted to 1,200 HV and 525 HV of CG steel correspondingly.
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