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AssigneeNippon Steel Corporation
InventorsEiji Tsuru, Takuya Hara, Hitoshi Asahi, Hideki Miyazaki, Tatsuya Yoshida
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A high-strength steel pipe excellent in formability and burst resistance wherein, when a high-strength steel pipe exceeding 850 N/mm2 in tensile strength is produced by a UOE method, a ratio (R/r) of an average radius of curvature in a range of 120 mm in a circumferential direction including a 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 preferably the ratio (R/r) is 0.90 to 2.0. Preferably, Vickers hardness of the base metal Hv, the minimum Vickers hardness at the HAZ Hz, pipe wall thickness t, and a peaking amount at the weld of the steel pipe before pipe expansion in a pipe expansion process δ satisfy the following expression, (1+0.005t|δ|)Hz<0.03584Hv2−25.34Hv+4712.
A high-strength steel pipe excellent in formability, characterized in that, when a high-strength steel pipe exceeding 850 N/mm2 in tensile strength is produced by a UOE method, a ratio (R/r) of an average radius of curvature in a range of 120 mm in a circumferential direction including a weld of the steel pipe before pipe expansion in a pipe expansion process (R) to a radius of the steel pipe after pipe expansion (r) is 0.65 to 2.0.
A high-strength steel pipe excellent in formability and burst resistance, characterized in that, when a high-strength steel pipe exceeding 850 N/mm2 in tensile strength is produced by a UOE method, a ratio (R/r) of an average radius of curvature in a range of 120 mm in a circumferential direction including a weld of the steel pipe before pipe expansion in a pipe expansion process (R) to a radius of the steel pipe after pipe expansion (r) is 0.90 to 2.0.
A high-strength steel pipe excellent in burst resistance, characterized in that, when a high-strength steel pipe 900 N/mm2 or more in tensile strength is produced by a UOE method, Vickers hardness of a base metal of the steel pipe Hv, the Vickers hardness at HAZ Hz, pipe wall thickness t, and a peaking amount at a weld of the steel pipe before pipe expansion in a pipe expansion process δ satisfy an expression (3),
Dependencies are inferred from the claim text.