OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 a b Fig. 2. Microstructures of St3 (a) and 3Cr2W8V (b) steels after aluminizing layer on St3 steel was 65 μm, which was comparable to the layers obtained by spray aluminizing and in molten salts (galvanic method) [17]. A layer with an average thickness of 50 μm and an uneven interface with the base metal were visible on the sample of 3Cr2W8V steel after aluminizing. Local extrema of the layer thickness, apparently, were the places of the steel surface melting and partial transition to the liquid state in these areas. This was also accompanied by increased diffusion in proportion to the increase in temperature. The latter was obviously caused by the passage of an exothermic metal reduction reaction. At the same time, the layer phase composition was similar to the composition on St3 carbon steel, where iron aluminides were additionally alloyed with Cr, W, and V. The low quality of the surface after aluminizing was due to the high reactivity of aluminum, accompanied by interaction with oxygen and other elements of atmospheric air [20]. Figure 3 shows the microhardness distribution over the distance after the boriding process of the both steels. The maximum microhardness on St3 steel was observed on the layer at a distance up to 10–15 μm from the surface and reached 1,919.6 HV, which is typical for boriding due to the formation of solid iron borides. The maximum value of 1,684.8 HV was observed at a distance of 15 μm from the surface on 3Cr2W8V steel, probably in the zone with the highest concentration of borides. Fig. 3. Microhardness distribution over the layer depth on steels after boriding
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