OBRABOTKAMETALLOV Vol. 26 No. 3 2024 technology Fig. 7. Hardness distribution in the welded joint after various treatment modes Fig. 8. Welded pipe joints after flattening + bending test: 1 – original pipe; 2 – welded pipe in condition after tempering; 3 – welded pipe in condition after complex heat treatment normalization + tempering The ultimate strength of welded joints made with different welding parameters is shown in Table 3 based on the test results of three specimens in each series. According to the test results, the ultimate strength of joints made from 0.15C-5Cr-Mo steel is within 400–470 MPa, which is significantly higher than the base metal. During tensile tests, the destruction of the metal of a pipe made of steel 0.15C-5Cr-Mo occurred at a distance of 60–70 mm from the joint. Results and discussion Technological parameters of resistance butt welding of pipes, changed in the course of our research, show that upsetting pressure and sparking allowance affect the final strength properties of the welded joint (Table 3). Resistance butt welding is a two-stage electric resistance welding process. In the initial stage of welding, the two parts to be welded are fully heated to obtain adequate plastic deformation capability. In the upsetting stage, after the flashing process is completed, sufficient upset force is applied to the joint
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