| 摘要 |
PROBLEM TO BE SOLVED: To provide a seamless steel pipe having high tensile strength and excellent also in toughness, ductility and weldability. SOLUTION: This high tensile strength steel pipe excellent in toughness, ductility and weldability has a composition comprising by mass, 0.10 to 0.40% C, <=0.8% Si, 0.5 to 1.3% Mn, 0.03 to 0.20% V, <=0.05% Al, >0.01 to 0.03% M and, if required, Cu, Cr, Mo, Ti, Nb, or the like, and the balance Fe with inevitable impurities, in which Ceq defined by the following formula satisfies the condition of 0.40 to 0.55 and has tensile strength of >=590 MPa, Charpy absorbed energy at -20 deg.C of >=30 J and elongation of >=20%.
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