The objective of this study was to investigate the effect of nitriding on the change in element dimensions of full circles and C-circles of 42CrMo4 steel. Nitriding is based on the enrichment of the surface layer with nitrogen, which alone or in compounds causes surface hardening. The enrichment of the surface layer leads to an increase in volume and thus to a change in element dimensions and the development of residual stresses. The change in element geometry can also be affected by the presence of residual stresses in the material.
Experimental work includes measurement of residual stresses in the initial state of the steel, after annealing to relieve residual stresses, and after nitriding. A 3D coordinate measuring machine was used to measure shapes and dimensions, and an optical microscope and a scanning electron microscope were used to characterize the microstructure.
The results of the study show that the change in the dimensions of the subjects was most affected by nitrogen, which leads to the formation of a surface layer of nitrides through diffusion effects. After nitriding, only compressive stresses remain on the surface, which increases the durability and dynamic hardness of the surface. During heat treatment, the new thermal stresses have no noticeable effect on the change of element dimensions due to the non-uniform cooling in depth.
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