OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 Metallographic studies of the structure and diffusion layer of 0.5C-Cr-Ni-Mn steel showed the presence of a diffusion layer with a thickness of 130 µm and 220 µm at 3- and 4-hour borocoppering, respectively (Fig. 2, b, Fig. 3. b). The microhardness was 1,800–1,500 HV at 3-hour soaking and 2,000–1,650 HV at 4-hour soaking. When conducting diffusion saturation with boron and copper of specimens from Steel 45 (0.45% C), Steel U10 (1.0% C) and 0.5C-Cr-Ni-Mn steel for 5 hours, an increase in the thickness of the diffusion layer by 10–15 µm is observed (Fig. 5). Fig. 4, a shows the structure of Steel 45 (0.45% C), where, in contrast to the previous borocoppering modes, the layer has a pronounced needle-like structure in the form of enlarged needles with a rectilinear direction to the core of the specimen. There is an increase in microhardness in the near-surface part of the layer, where its maximum value is 2,100 HV (Fig. 6, a). a b c Fig. 4. Microstructure of the diffusion layer after complex surface saturation with boron and copper for 5 hours of exposure: a – Steel 45 (0.45% C), layer thickness is 170 µm; b – Steel U10 (1.0% C), layer thickness is 155 µm; c – 0.5C-Cr-Ni-Mn steel, layer thickness is 230 µm Fig. 5. The thickness of the diffusion layer formed after borocoppering of Steel 45 (0.45% C), Steel U10 (1.0% C), and 0.5C-Cr-Ni-Mn steel for 3, 4 and 5 hours On the surface of the specimens from Steel U10 (1.0% C), after 5 hours of borocoppering, the diffusion layer loses its needle-like structure and takes the form of a continuous layer, as evidenced by Fig. 4b. The increase in thickness was 15 µm, and the maximum value of microhardness was equal to 2,000 HV (Fig. 6, b).
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