THE CHROMIUM AND TUNGSTEN DISTRIBUTION IN THE DIFFUSION LAYER OF STEEL X35CrNi2-3 DURING THERMОDIFFUSION SATURATION

Abstract

Chemical-thermal treatment (CHT) of structural parts operating under conditions of wear, friction, shock loads make it possible to obtain a unique combination of surface and core properties of the product. However, such traditional CTO methods as carburizing and nitriding, while improving the mechanical characteristics of the surface, are not suitable for all types of steels. Diffusion metallization methods, in particular, thermal diffusion chromium plating, are more effective in terms of the achieved set of properties. Currently, chromium plating is carried out both by saturation of the metal with one element – chromium, and by multi-element mixtures. The article describes the technology of thermal diffusion saturation of steel X35CrNi2-3 with chromium and tungsten at a temperature of 1000 °С. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis (XMS) of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied on an optical metallographic microscope Axio Observer D1.m. X-ray phase analysis was carried out on a Rigaku Ultima IV diffractometer. The hardness measurement was carried out on an FM-800 microhardness tester at a load of 100 g. Data were obtained on the qualitative and quantitative distribution of chromium and tungsten in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists of a substitutional solid solution based on Cr–Fe with a bcc lattice, chromium and tungsten carbides. The depth of the outer coating on the sample was about 20 μm, the depth of the diffusion layer in the base metal was 50–55 μm. The absence of a decarburized area in the surface layer of the base metal was noted. The average diffusion coefficients of chromium in the α-phase of chromium were determined to be DCr = 3,58·10–13 m2/s; in the γ-phase of iron DCr = 2,83·10–15 m2/s. The microhardness of the outer surface layer was 1800–2000 HV, the diffusion layer in the base metal was 1300–550 HV, and the base metal was about 540–510 HV.