ULTRAHIGH STEEL SHEET FOR LINE PIPE, ITS PRODUCTION METHOD AND WELDED STEEL PIPE

PROBLEM TO BE SOLVED: To provide a steel sheet having excellent unstable ductile fracture resistance in spite of its ultrahigh strength satisfying a tensile strength of ≥760 MPa, to provide a steel pipe for a line pipe, and to provide a method for producing the steel sheet. SOLUTION: In the ultrahig...

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Bibliographische Detailangaben
Hauptverfasser:	HAMADA MASAHIKO, OKAGUCHI HIDEJI
Format:	Patent
Sprache:	eng
Schlagworte:	ALLOYS CHEMISTRY FERROUS OR NON-FERROUS ALLOYS GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS METALLURGY METALLURGY OF IRON MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS TREATMENT OF ALLOYS OR NON-FERROUS METALS
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Beschreibung
Zusammenfassung:	PROBLEM TO BE SOLVED: To provide a steel sheet having excellent unstable ductile fracture resistance in spite of its ultrahigh strength satisfying a tensile strength of ≥760 MPa, to provide a steel pipe for a line pipe, and to provide a method for producing the steel sheet. SOLUTION: In the ultrahigh strength steel sheet and steel pipe for a line pipe, the metallic structure in the surface layer part equivalent to 5 to 30% of the sheet thickness in a depth from the surface or back surface is the one comprising a tempered martensitic structure by ≥80%, the metallic structure other than that of the surface layer part is a bainitic structure, a martensitic structure, or a mixed structure thereof, and also, the average old austenite grain size is ≤18 μm. COPYRIGHT: (C)2006,JPO&NCIPI