CORROSION RESISTANCE OF CHROMOSILICIDE COATINGS ON STEEL 45 IN DIFFERENT AGGRESSIVE ENVIRONMENTS

Abstract

In the work, diffusive chromosilicide coatings were applied to steel 45 by a gas method in a specially designed installation, which had a special reaction chamber of a new design. The process was carried out for 6 hours in a closed reaction environment at the pressure of the active gas phase and a temperature of 1323K. Ferrosilicon, chromium, and carbon tetrachloride powders were used as starting reagents for applying diffusion coatings. The metallographic studies were carried out on a Neophot 21 optical microscope. It was established that complex coatings with the participation of chromium and silicon, applied to the surface of steel 45, according to the data of microstructural analysis, consist of an outer layer up to 20∙10-6 m, which contains carbides of chromium Cr23C6, Cr7C3 and an inner layer of 80∙10-6 m, which is a solid solution of silicon and chromium in α-iron. The corrosion resistance of chromosilicide diffusion coatings was studied in 10–15% solutions of hydrochloric, phosphoric, acetic, and nitric acids, in a 3% solution of sodium chloride, and in technical water. It is shown that diffusive chromosilicide coatings applied to carbon steels increase corrosion resistance in the tested solutions by 2.5–750 times. It is possible to increase the corrosion resistance of diffusion coatings due to the introduction of inorganic substances (sodium molybdate). The introduction of 3g/l of sodium molybdate into 10% solutions of phosphoric, hydrochloric and sulfuric acids increases the corrosion resistance of chromo-silicide coatings by 4, 7 and 36 times, respectively. It has been shown that chromosilicid coatings can be recommended for the protection of machine parts operating in various aggressive environments.