| 摘要 |
The present invention provides, in a method of producing such a high-strength steel pipe for line pipe use as to exceed 850 N/mm<2> in tensile strength by a UOE method, a method of producing a high-strength steel pipe for line pipe use, being so excellent in formability and burst resistance as to prevent cracking and a rupture at a seam weld in a pipe expansion process and as not to incur a brittle rupture from a seam weld even when an internal pressure load is imposed during the use of the steel pipe. The present invention is: a high-strength steel pipe excellent in formability and burst resistance, characterized in that, when a high-strength steel pipe exceeding 850 N/mm<2> in tensile strength is produced by a UOE method, the ratio (R/r) of the average radius of curvature in the range of 120 mm in the circumferential direction including the weld of the steel pipe before pipe expansion in a pipe expansion process (R) to the radius of the steel pipe after pipe expansion (r) is 0.65 to 2.0, and further the ratio (R/r) is 0.90 to 2.0; and yet further a steel pipe excellent in burst resistance, characterized in that the Vickers hardness of the base metal Hv, the minimum Vickers hardness at the HAZ Hz, the pipe wall thickness t, and the peaking amount at the weld of the steel pipe before pipe expansion in a pipe expansion process delta satisfy the following expression, <DF>(1 + 0.005t delta ) Hz < 0.03584Hv<2> - 25.34Hv + 4712. </DF> <IMAGE> |
