Influence of carbon content in steel on the composition and properties of the layer during thermodiffusion chromium plating in mixtures with additives of thermal emitter oxides

The paper presents a comparative study of the structure and properties of thermal diffusion chromium coa-tings on steels with different carbon contents obtained by saturation in a process mixture containing scheelite powder (CaWO4) as an activating additive, which is an emitter of oxygen anions and electrons during heating. The aim of the work was to establish the influence of the thermal diffusion chromium plating method proposed by the author on the process of chromium coating formation on steels with different carbon contents. The composition of the obtained diffusion layers was studied using a JEOL JSM-6460 LV electron microscope equipped with an Oxford Instruments attachment for qualitative and quantitative microanalysis. The microstructure was studied using an Axio Observer D1.m optical metallographic microscope. X-ray phase analysis was performed using a Rigaku Ultima IV diffractometer in α-radiation of an iron anode. Microhardness measurements were performed using an FM-800 microhardness tester. The results of the study show that the steel composition, namely the carbon content, as with the standard technology of thermal diffusion chromium plating, has a significant effect on the size and composition of the forming thermal diffusion layer. With an increase in carbon content from 0.12 to 0.75 wt.%, the depth of the total diffusion of chromium into the metal decreases by more than 2 times. At the same time, a sharp increase in the carbide and nitride phases and a corresponding increase in hardness from 950 HV0.05 to 2100 HV0.05 are noted in the composition of the diffusion layer. Phase analysis of coatings obtained by thermal diffusion chromium plating with thermionic current showed the predominance of chromium nitrides instead of chromium carbides in the standard chromium plating technology. Such a change may be associated with an increase in the directed diffusion flow to the saturated part and a weakening of the counter diffusion of carbon from the base metal.