HIGH-STRENGTH STEEL PIPES WITH LOW RATIO OF YIELD STRENGTH TO ULTIMATE STRENGTH, WELDED WITH ELECTRIC CONTACT WELDING, STEEL STRIP FOR PIPES, WELDED WITH ELECTRIC CONTACT WELDING, AND MANUFACTURING METHODS THEREOF Russian patent published in 2016 - IPC C21D8/10 C21D8/02 C21D9/08 C21D9/50 C22C38/00 C22C38/58 

FIELD: technological processes.

SUBSTANCE: invention relates to high-strength steel pipe with low ratio of yield strength to ultimate strength, welded with electric contact welding, with ratio of yield strength to ultimate strength of 80 % or less and TS 655 MPA or higher and its manufacturing method. In particular, steel material of composition, including, wt%: 0.38-0.45 C, 0.15-0.25 Si, 1.0-1.8 Mn, 0.03 or less P, 0.03 or less S, 0.01-0.07 sol. Al and 0.005 or less N by weight is subjected to rough and finish rolling, at which initial temperature is 950 °C or lower and final temperature is 820-920 °C, thus hot-rolled steel strip is obtained. Strip is wound at temperature of 650-800 °C, then unwound, molded and welded with electric contact welding at room temperature.

EFFECT: manufacturing of steel pipe with small changes of properties in longitudinal direction ΔTS 20 MPa or less, low ratio of yield strength to ultimate strength of 80 % or less and high strength, id est, yield strength YS 379-552 MPa and ultimate tensile strength TS 655 MPA or higher.

12 cl, 3 tbl, 2 dwg