ULTRAHIGH STRENGTH STEEL PIPE WITH EXCELLENT TOUGHNESS OF WELD ZONE, AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a steel pipe having excellent toughness at low temperature and ≥900 MPa (exceeding API Standard X100) tensile strength and also to provide its manufacturing method.;SOLUTION: In the high strength welded steel structure with excellent toughness of weld zone, integranular bainite is formed using compound inclusions as nuclei in a weld metal zone or in a weld heat-affected zone, and the nuclei are: compound sulfides which consist of two phases of oxides and sulfides composed essentially of Mn sulfide and sulfides composed essentially of Cu sulfide both precipitated in the periphery of the oxides; or compound inclusions in which nitrides are further precipitated in the compound sulfides.;COPYRIGHT: (C)2003,JPO