The package of the applied programs with base of the thermodynamic data is used and the theoretical analysis of physical and chemical conditions of complex-saturation carbon steel by silicon and chrome in medium of chlorine in the closed reactionary space is carried out at the lowered pressure of a gas phase. Simultaneous saturation of steel 40 with chrome and silicon in chlorine atmosphere for 6 hours at a temperature of 1323 K and a pressure of $10^{2}$ Pa of the gas phase is carried out in this work. By means of the x-ray diffraction studies, it is found that, under the assumed conditions of saturation on the steel 40 surface, diffusion layer with thickness of 100–110 µm is formed, which corresponds to the phase of the corresponding chromium carbides Cr$_{23}$C$_{6}$ and Cr$_{7}$C$_{3}$ doped with silicon, and a solid solution of chromium and silicon in $\alpha$-iron. The corrosion studies carried out in this work show that chromosilicide coatings applied onto carbon steel 40 are less stable in solutions of 10% hydrochloric and sulphuric acids, and the most stable in solutions of nitric acid.