Synthesis of chromium carbide coatings on carbon steels in molten salts and their properties

Chrome plating from the melt of NaCl-KCl-CrCl2 on substrates of carbon steels is studied and the chromium carbide formation with the Cr23C6, Cr7C3, and Cr3C2 composition is revealed. The controlled potential electrolysis parameters resulting in the chromium carbide formation with various compositions on the steel surface are determined. The currentless transfer method is used for the synthesis of chromium carbide coatings with the Cr7C3 composition on grades St3 and U9 steels. The coating with the given composition is demonstrated to reduce by some orders the corrosion rate of steel substrates within the concentrated mineral acids. It is found that the composition of St3-Cr7C3 coating is stabler to concentrated acids than the composition of U9-Cr7C3 coating. The Cr7C3 coating has a high microhardness (21-23 GPa) and increases the wear resistance of samples practically by an order.