Features of the formation of a diffusion layer and the mechanism of diffusion during boronizing of steels

Abstract

The paper presents the results of studies on the formation of a diffusion layer during the boriding of steel with a carbon content of 0.38 wt%. The study of diffusion coatings by SEM and TEM methods allows one to more clearly determine the mechanisms of diffusion of boron atoms and the formation of diffusion boride coatings. Diffusion of boron in the processes of diffusion boriding of iron-carbon alloys proceeds by a mixed mechanism: the delivery of active boron atoms to the diffusion front proceeds along the grain and phase boundaries. The reaction mechanism is realized by a gradual substitution of carbon with boron in iron carbides. Due to the continuous diffusion of boron, the reaction boundary is constantly moving in the direction from the surface to the core of the saturated material. In this case, as the diffusion proceeds, the concentration of carbon atoms under the boride layer constantly increases. This provides resistance to diffusion of boron atoms by the atomic mechanism and provokes diffusion by the reaction mechanism.