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

Abstract

Known methods of chemical-thermal treatment of structural parts, such as carburizing, nitriding, diffusion metallization technologies, make it possible to obtain a unique combination of surface and core properties of the product. The positive experience of using methods of multi-element diffusion saturation opens up prospects for the development of methods for complex saturation. The article describes the technology of thermal diffusion saturation of steel X35CrNi2-3 with chromium and molybdenum at a temperature of 1000 °C. 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 molybdenum in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr–Fe–Mo with a bcc lattice and chromium and molybdenum 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 about 25 μm. The absence of a decarburized area in the surface layer of the base metal was noted. The average diffusion coefficients of chromium and molybdenum in the α-phase of chromium were determined DCr = 6.6·10–15 m2/s and DMo = 4.35·10–16 m2/s respectively; in the γ-phase of iron DCr = 2.95·10–15 m2/s, DMo = 2.48·10–16 m2/s respectively. The microhardness of the outer surface layer was 1400–1980 H, the diffusion layer in the base metal was 1000–600 HV, and the base metal was about 540–510 HV.