| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a welded steel pipe for line pipe having≥900 MPa tensile strength by which cutting crack resistance can be improved without deteriorating toughness, particularly crack arrest property, while keeping high deformability and further a strength of a joint equal to or higher than that of a base material can be attained without decreasing toughness of a weld metal. <P>SOLUTION: A steel sheet having≥900 MPa tensile strength and≤85% yield ratio, which has specific components and also has a microstructure characterized as follows, is used: any of (ferrite plus bainite), (ferrite plus martensite) and (ferrite plus bainite plus martensite) includes≥90% by area fraction; an area ratio of ferrite is 10 to 50%; and an average grain size of cementite in bainite and/or martensite is≤0.5μm. After the steel sheet is formed into a pipe shape by cold working, welding is carried out in such a way that a chemical composition of a weld metal consists of specific components by a hybrid welding process combining a laser using CO<SB>2</SB>gas shield with a gas shield arc welding using Ar-CO<SB>2</SB>gas shield. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
