OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 of welded and non-welded structures and parts (composition, in wt. %): Fe ≈ 97, C 0.14-0.22, Si 0.15-0.3, Mn 0.4-0.65). 3Cr2W8V steel is used for a heavily loaded press tool utilized for hot deformation of alloyed structural steels and heat-resistant alloys (composition, in wt. %): Fe ≈ 87, C 0.3-0.4, Si 0.15-0.4, Mn 0, 15-0.4, Cr 2.2-2.7, W 7.5-8.5, V 0.2-0.5, Mo up to 0.5). The powder mixture was poured into the crucible along with the test samples; then the crucible was packed and sealed with a fusible seal from the top. The crucibles were cooled in the open air at room temperature. At the end, the crucibles were unpacked and the samples were cleaned from the remnants of the saturating mixture. The composition and structure of the diffusion layer were determined on a JSM-6510LV JEOL (Japan) scanning electron microscope with an INCA Energy 350 Oxford Instruments (Great Britain) microanalysis system at the Progress Science Center, East Siberia State University of Technology and Management. The phase composition on the samples’ surfaces was determined by a D8 ADVANCE Bruker AXS X-ray diffractometer in copper radiation with a shooting interval of 10-70° at the Science Center of the BIP SB RAS. The microhardness test of the obtained layers was carried out by a PMT-3M microhardness tester. The load was 50 g. The Nexsys ImageExpert MicroHardness 2 software package (9450-76 State Standard) was used to calculate the microhardness values. Microstructures were photographed by a METAM RV-34 metallographic microscope with an Altami Studio digital camera (Russia). The Nexsys ImageExpert Pro 3.0 software package was used to determine the thickness of the diffusion layer. Results and discussions The boriding and aluminizing processes were carried out on St3 and 3Cr2W8V steel samples at a temperature of 900 °C for 2 hours. Figures 1 and 2 show microphotographs of the steels structures after TCT. These fi gures clearly show the acicular structure of the borided layers. The thickness of the resulting diffusion layer on St3 steel was 35 μm, and on the alloyed steel it was 15 μm. It is known that boriding of low-carbon steel under the same time-temperature modes in metal-oxide-containing mixtures (based on boron and aluminum oxides) provides a layer thickness of 50 μm [16]. A considerably thinner layer was formed on 3Cr2W8V steel compared to the low-carbon steel. This was due to the high concentration of alloying elements, which hindered the diffusion of boron. The resulting layer thickness was consistent with the borated layers obtained by the liquid method and in pastes of various compositions [16]. Figures 2, a and 2, b show the structures of the studied steels after aluminizing. A more even surface layer was formed on St3 steel, consisting mainly of Al5Fe2. At the boundary with the base metal, AlFe, AlFe3 phases and a solid solution in α-Fe were gradually formed [17–19]. The thickness of the diffusion a b Fig. 1. Microstructures of St3 (a) and 3Cr2W8V (b) steels after boriding
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