INFLUENCE OF HIGH TEMPERATURE OXIDATION ON CORROSION RESISTANCE OF CHROMOSYLICATED STEEL 45

Abstract

Purpose. Improving the heat resistance and corrosion resistance of carbon steels can be achieved by applying to their surface coatings based on molybdenum and silicon, niobium and silicon, vanadium and silicon, chromium and silicon, which form on the surface protective films of oxides. In this work properties of chromosilicide diffusion coatings applied to steel 45 obtained by the gas method are investigated. Methodology. Diffusion chromosilicide coatings were applied to steel 45 by the gas method. The process was carried out for 6 hours in a closed reaction medium at the pressure of the active gas phase (106 Pa) and a temperature of 1323K. In the work wad studied phase and chemical compositions of diffusion coatings. The heat resistance of the coatings was studied in a specially designed shaft furnace. Corrosion tests were performed by massometric method .The electrochemical behavior of steel and coated steel was studied by the method of removing polarization curves on the potentiostat PI-50.1.1. Results. X-ray diffraction layer analysis revealed that the diffusion layer on the surface of steel 45 consists of two zones - the outer (10–15) 10-6 m, which contains chromium carbides Cr23C6 and Cr7C3 and inner (60–80) 10-6 m, which consists of a solid solution of silicon and chromium α-Fe. The total thickness of the coatings is 100 μm. Microhardness – 19.5 GPa. It was found that chromosilicide coatings obtained by the gas method have high heat resistance up to 1000 С. It is shown that diffusion chromosilicide coatings oxidized at temperatures of 700–800С have higher corrosion resistance in various aggressive environments and a more stable passive state than non-oxidized ones. The degree of protection reaches 99,92–99,99%. Based on the research, a new method of diffusion coatings on the surface of carbon steels with subsequent oxidation was proposed. Practical value. Chromosilicide coatings can be recommended for the protection of machine parts operating at elevated temperatures in various aggressive solution. References 20, tables 1, figures 3.