Effect of Modes of Diffusion Metallization in the Medium of Low-Melting Liquid Metal Solutions on the Formation of Ni–Cr Coatings on Steels

Abstract—Diffusion saturation of the St3, 40Kh, 40Kh13, and 30KhGSN2A steels with nickel and chromium in a Pb–Li melt of eutectic composition is carried out. The kinetics of coating formation is assessed. On the 40Kh and 30KhGSN2A steels, the coating consists of a surface carbide layer with a microhardness of 2000 HV0.01 and a transition solid-solution layer. On the St3 and 40Kh13 steels, the coating is formed on the basis of solid solutions, and the microhardness is 200 HV0.01. The elemental composition of the materials being coated affects the formation of the coating: the thickest coatings are on the St3 steel, and the thinnest ones are on the 40Kh13 steel. The chromium content on the surface of coatings on the 40Kh and 30KhGSN2A steels was 80 wt %. The maximum nickel content is detected at a depth of 4–5 μm and amounts to 21 wt % for 30KhGSN2A steel and 13 wt % for 40Kh steel. For samples made of 40Kh13 and St3 steels, the chromium content is 8 and 14.5 wt %, respectively. At the same time, the nickel content on the surface reaches 40 wt %. The dependence of the coating thickness on the diffusion saturation temperature has exponential character, and the dependence of thickness on time has parabolic character. The maximum coating thickness is obtained at a temperature of 1070°C and holding time of 480 min. However, with increasing holding time, the intensity of coating formation decreases.