OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 Introduction The tasks of improving the reliability, operability and durability of machine parts, structures and tools are among the priorities in science and technology. To solve these problems, it is necessary to develop and implement effective methods that can improve many operational characteristics (corrosion resistance and wear resistance) by surface hardening. One of the most common methods of surface hardening is thermochemical treatment (TCT), which is aimed at improving a wide range of physical and mechanical properties during the operation of machine parts and tools. The essence of any TCT method consists in thermal and chemical effects on the material in order to change the composition, structure and properties of the surface layer. From the analysis of the literature data, it follows that one of the most common methods of TCT is boriding [1–6]. The boriding process has been known for more than half a century, but is not widely used compared to carburizing [7–10], nitriding and nitrocarburizing [11–14]. As a result of saturation of iron-carbon alloys with boron, layers with high hardness (1,600–2,000 HV) are formed on the surface. The widespread use of boriding in mechanical engineering is limited by high brittleness and tendency to cracking of surface layers after various chemical and thermal processing methods [15–17]. There are several ways to reduce the brittleness of the boride layer: 1) obtaining single-phase layers consisting of Fe2B phase; 2) obtaining thinner layers; 3) the use of such elements as chromium, copper, nickel, aluminum, etc. in the composition of the saturating mixture together with boron [21–24]. Of particular interest is one of the methods of TCT – borocoppering. This method is aimed at increasing the thickness of the diffusion layer, as well as increasing the plasticity of the diffusion layer. The authors of [21–23] found that an increase in the concentration of copper in the composition of the saturating mixture contributes to an increase in the thickness of the diffusion layer. The purpose of this work is to determine the temperature-time parameters of diffusion borocoppering, which contribute to the formation of diffusion layers with a maximum thickness. The paper considers the results of surface hardening of carbon and alloy steels (for example, Steel 45 (0.45% C), Steel U10 (1.0% C), and 0.5C-Cr-Ni-Mn steel) by high-temperature soaking in powder mixtures containing boron and copper. The purpose of this work is to study the structure of the diffusion layer depending on the duration of complex saturation of the surface of specimens made of Steel 45 (0.45% C), Steel U10 (1.0% C) and 0.5C-Cr-Ni-Mn steel with boron and copper. Research methodology The diffusion saturation process was carried out in a powder medium. Steel 45 (0.45% C), Steel U10 (1.0% C) and 0.5C-Cr-Ni-Mn steel were used as test specimens, the chemical composition of which is shown in Table 1. Ta b l e 1 Chemical composition of Steel 45 (0.45% C), Steel U10 (1.0% C), 0.5C-Cr-Ni-Mn, wt.% C Si Mn Ni S P Cr Cu Fe Mo Steel 45 (0.45% C) 0.42–0.5 0.17–0.37 0.5–0.8 up to 0.25 up to 0.04 up to 0.035 up to 0.25 up to 0.25̴ 97 – Steel U10 (1.0% C) 0.96–1.03 0.17–0.33 0.17–0.33 up to 0.25 up to 0.028 up to 0.03 up to 0.2 up to 0.25̴ 97 – 0.5C-Cr-NiMn steel 0.5–0.6 0.1–0.4 0.5–0.8 1.4–1.8 up to 0.03 up to 0.03 0.5– 0.8 up to 0.3̴ 95 0.15–0.3
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