OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 After borocoppering of Steel 45 (0.45% C) for 4 hours, the layer thickness was 140 µm, which is 20 µm greater compared to the soaking this steel for 3 hours (Fig. 3, a). The microhardness was 2,000 HV at the surface, followed by a decrease to 1,600 HV at the layer/base interface. There is a fusion of needles at the base with the formation of a continuous layer. There is no carboboride phase adjacent to the boride needles. The transition zone is more clearly represented in the form of a light ferrite layer, where the maximum concentration of boron reaches 4 %, and then it gradually decreases towards the core of the specimen. The steel structure retains proeutectoid ferrite (light inclusions); martensite with a small content of residual austenite is also observed. On the surface of the carbon tool Steel U10 (1.0% C), after 3 hours of TCT, a diffusion layer with a thickness of 110 µm was obtained, the hardness of which was 1,975–1,575 HV (Fig. 2, b). The layer consists of tightly pressed needles with an unexpressed transition zone, which is represented by perlite with low boron content. The steel structure consists of a plate-like perlite surrounded by a thin cementite mesh. It is necessary to note the presence of light coagulated inclusions, apparently being austenite. After borocoppering of Steel U10 (1.0% C) for 4 hours, a diffusion layer with a thickness of 140 µm was obtained, which is 30 µm greater compared to the soaking this steel for 3 hours (Fig. 3, b). The microhardness also increased slightly to 2,050 HV at the surface, followed by a decrease to 1,600 HV at the layer/base interface. The microstructure indicates the fusion of needles and the formation of a continuous layer in the upper and middle part of the layer with the preservation of the needle structure at the layer/base interface. The presence of a transition zone is not observed, and the microstructure of the base metal is represented by a lamellar perlite with a cementite mesh. a b c Fig. 2. Microstructure of the diffusion layer after complex surface saturation with boron and copper for 3 hours of soaking: a – Steel 45 (0.45% C), layer thickness is 120 µm; b – Steel U10 (1.0% C), layer thickness is 110 µm; c – 0.5C-Cr-Ni-Mn steel, layer thickness is 130 µm a b c Fig. 3. Microstructure of the diffusion layer after complex surface saturation with boron and copper for 4 hours of soaking: a – Steel 45 (0.45% C), layer thickness is 160 µm; b – Steel U10 (1.0% C), layer thickness is 140 µm; c – 0.5C-Cr-Ni-Mn steel, layer thickness is 220 µm
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