OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 Materials and methods The base material used in this study was a seamless pipe with an outer diameter of 25 mm and a wall thickness of 2.5 mm. The pipe material was steel 0.15C-5Cr-Mo (Table 1), delivered in a normalized and tempered state in accordance with GOST 550-75. When analyzing the chemical composition of pipe materials, the following measuring instruments and testing equipment were used: X-ray spectrometer SRM-25, express carbon analyzer AN-7529. Mechanical properties of as delivered material are presented in Table 2. To determine the mechanical properties of a pipe steel, 3 samples were taken in accordance with industry standards [11]. For welding, a resistance butt welding machine MSO-201N was used, the welding current was 7,400– 8,000 A. The process of resistance welding of pipes is shown in Fig. 1. For welding, a resistance butt welding machine MSO-201N was used, the welding current was 7,400– 8,000A. The welding process is shown in Fig. 1. During the research, specimens were examined after Ta b l e 1 Chemical composition of pipes for welding Steel grade Elemental content, % C Si Mn Сr Mo Ni S Р 0.15C-5Cr-Mo According to GOST 20072-74 < 0.15 < 0.5 < 0.5 4.5– 6.0 0.45– 0.60 << 0.6 < 0.025 < 0.030 In fact 0.1 0.35 0.22 5.51 0.52 0.35 0.012 0.012 Ta b l e 2 Mechanical properties of 0.15C-5Cr-Mo steel pipe Assortment Yield strength, σ0.2, MPa, min Ultimate strength, σu, MPa, min Percentage elongation, δ5, %, min Percentage reduction of area, ψ, %, min Hardness, HB, max Pipe according to GOST 550-75 216 421 22 50 170 In fact 220 450 25 54 128 Fig. 1. Pipe welding on the MСO-201Н machine
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