Influence of the Combined Chemical Thermal Treatment on the Corrosion Resistance of Steel Products

The influence of the combined chemical thermal treatment (CCTT) of steel products, including carburizing, diffusion saturation with chromium, and quenching, on the corrosion resistance of steel products in a 30% aqueous solution of HCl and in 3% NaCl is considered. The treated materials are St3, 40Kh, 40Kh13, and 20Kh13 steels. The CCTT technology is shown to provide coatings with the thickness from 7 to 27 μm, and the microhardness of the surface of the coated specimens reaches 24 000 MPa depending on the CCTT temperature. The elemental composition of the coated material, CCTT conditions, and composition of the corrosion-active medium affect the corrosion rate. The steels without coatings have a lower corrosion resistance than the materials subjected to CCTT. A decrease in the corrosion rate is directly proportional to an increase in the chromium content and a decrease in the carbon content in the coated material. The corrosion rate decreases most efficiently in a NaCl medium. For a NaCl solution, the corrosion rate of specimens of St3 steel decreases by 11.6 times, that of 40Kh specimens decreases by 8.22 times, that of 40Kh13 specimens decreases by 4.56 times, and the corrosion rate of 20Kh13 specimens decreases by 4.1 times. For a 30% aqueous solution of HCl, the corrosion rate of St3 specimens decreases by 4.6 times, that of 40Kh specimens decreases by 4.4 times, that of 40Kh13 specimens decreases by 3.99 times, and the corrosion rate of 20Kh13 specimens decreases by 3.84 times. The CCTT temperature affects the corrosion resistance. The corrosion rate in 3% NaCl is 0.08 g m^–2 h^–1 at a CCTT temperature of 1000°C. The corrosion rate decreases to 0.059 g m^–2 h^–1 with increasing CCTT temperature to 1070°C. The effect of the CCTT temperature on other materials under study was analogous.