Influence of diffusion alloying of structural steels by nickel and copper in the medium of low-melting liquid-metal solutions on their corrosion resistance

Abstract

The paper considered the effect of Ni-Cu-based coatings obtained by diffusion metallization from a medium of low-melting liquid metal solutions on corrosion resistance of structural steels. It was revealed that diffusion saturation of Ni-Cu steels U8, Kh12MF, 40Kh, steel 20 formed diffusion coatings with a thickness of 10-42 μm on their surface. Thickness of the coatings depended on the modes of diffusion saturation and the coated material. It was found out that corrosion resistance of the coated materials increases in the environment of 30 % aqueous HCl and 3 % NaCl solutions with rise of the diffusion saturation temperature. The maximum corrosion resistance was obtained after diffusion saturation at the temperature of 1070 °C. Ni-Cu-based coatings allow to reduce the corrosion rate of steels in the NaCl environment: for the steel U8 by 26.21 times, for the steel Kh12MF by 21.48 times, for the steel 40Kh by 18.46 times, for the steel steel 20 by 13.9 times. Corrosion rate of steels in HCl environment is also reduced: for the steel U8 by 20.23 times, for the steel Kh12MF by 20.06 times, for the steel 40Kh by 17.35 times, for the steel 20 by 11.45 times. It was revealed that chromium-alloyed steels are undergone additional alloying coating with chromium, diffusing from the coated sample, which allows to obtain a minimal corrosion rate in both HCl and NaCl environments. Thus, the corrosion rate of steel Kh12MF after Ni-Cu coating in NaCl was 0.025 g/(m 2 •h), in HCl -0.289 g/(m 2 •h). The highest corrosion rate was detected on the samples made of U8 steel: in NaCl 0.032 g/(m 2 •h), in HCl -0.039 g/(m 2 •h).