OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 Figure 4 shows the microhardness distribution over the distance after the aluminizing process of the both steels. Fig. 4. Microhardness distribution over the layer depth on the steels after aluminizing The microhardness distribution curves obtained after the aluminizing process on 3Cr2W8V steel were the most promising. The maximum value of microhardness for St3 steel was 996 HV, and for 3Cr2W8V steel it reached rather a high value of 1,119 HV. An indicative increase in microhardness at a distance of 150– 180 μm from the surface was visible for the alloy steel. This local increase in microhardness corresponded to the transition zone directly under the layer, which supposedly indicated an increased content of chromium and tungsten carbides. Its concentration increased due to the displacement by aluminum diffusing from the surface. The substitution of the carbides deep into the base metal presumably occurred because of its mutual insolubility with aluminides [21]. The samples after TCT were subjected to XRD to determine the phase composition of the diffusion layers. Figure 5, a shows the XRD pattern after boriding of St3 steel, where FeB and Fe2B phases were revealed on the surface. Single Fe2B phase was distinguished after boriding of 3Cr2W8V steel (Fig. 5, b). a b Fig. 5. XRD-pattern of the surface after boriding: a – St3; b – 3Cr2W8V
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