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The technology of manufacturing pipe lines connection details of K60 strength class due to a flow chart, used at plants, includes hot stamping, welding and thermal treatment to ensure the specified complex of mechanical characteristics. The technology allows obtaining the details with high strength properties. Still the process of thermal treatment includes a labor-intensive quenching operation followed by high tempering, which increases significantly the production process cycle and increases scattering of properties among the details within a manufactured batch. Besides, at the quenching of thick-walled fittings, a local change of the detail geometry can happen caused by cooling with different speeds. Results of the study of thermal treatment influence, simulating heating before hot stamping and post-welding tempering, taking place at the connection details manufacturing by a specific technology considered. This technology excludes quenching for mechanical properties of thick rolled product of low carbon steel, alloyed by copper. The temperature parameters of the treatment determined to ensure obtaining properties of K60 strength class and high impact toughness (KCV –40 ≥200 J/sm 2 ) of 10–50 mm thick flat rolled product. It was shown, that for the studied steel the optimal complex of K60 strength class properties is obtained after treatment due to heating modes before stamping at 830–860 °С, followed by a high tempering at 600 °С. The thermal treatment of both sheets and 10, 16, 20, 40 and 50 mm thick plates due to elaborated modes ensured mechanical properties of K60 strength class and high resistivity against impact bending at negative temperatures. Series of tests for impact bending of 10 mm thick plate showed a high cold-resistance of the steel, as follows: KCV –50 ≥200 J/sm 2 , % В (KCV –50 ) ≥90 %, Т 50 = –55 °С.

The pipelines are one of most important section of the fuel and energy complex of Russia. About 75% of them are presented by gas pipelines of large diameter (1020–1420 mm) for the operating pressure up to 7.4 MPa. CNIIchermet after I.P. Bardin put a big contribution into creation of pipe steels and mastering of technologies for their production at steel-works of Russia. The Institute in cooperation with leading steels-works developed an array of pipe steel, which are successfully used at construction of modern gas and oil pipelines. Tendencies of requirements increasing to characteristics of steels for large diameter pipes for pipelines considered, creation stages of grade range of steels and technology of rolled products production analyzed. Main technological requirements for achieving mechanical properties high level determined. It was shown, that K60–K65 strength class steels meet requirements to northern pipelines for a pressure up to 11.8 MPa, to thick walled underwater pipelines for a pressure of 25.0 MPa and to pipes for seismic arears. Steel-works and pipe-manufacturing plant of Russia provide the production of longitudinal-welded pipes with wall thickness up to 40–60 mm with anticorrosion external coating and smooth internal coating.