Mechanism and features of formation of diffusion coatings based on carbide-forming elements on steels in medium of fusible liquid-metal solutions

It is established that the mechanism and kinetics of the diffusion coating formation, deposited in the medium of fusible liquid-metal melts, depend on the nature of the interaction of the elements forming the coatings with the elements of the coated steel. Two characteristic features inherent in the formation process of diffusion coatings on steels are described. The first feature is that the formation of coatings based on carbide-forming elements is characterized by intense diffusion of carbon from steel to the surface layers of the coating and blocking the diffusion of coating elements deep into the coated material. The second feature of the formation mechanism of coatings based on carbide-forming elements is that the blocking effect of carbon depends on the amount of carbon in steel, thermal stability of carbides of the coating elements, temperature and duration of the process. At the same time, the structure of the formed coating is characterized by the presence of an adsorbed layer, a carbide layer, a transition zone and a decarbonized zone. A scheme for the formation of diffusion coatings based on carbide-forming elements is presented. Formulas for calculating the value of the diffusion fluxes and thickness of the coating are given, and options for forming the coatings depending on the value of the diffusion fluxes are discussed.