HIGH-STRENGTH STEEL SHEET AND HIGH-STRENGTH WELDED STEEL PIPE EXCELLING IN DUCTILE FRACTURE PERFORMANCE AND PROCESS FOR PRODUCING THEM

Title:

HIGH-STRENGTH STEEL SHEET AND HIGH-STRENGTH WELDED STEEL PIPE EXCELLING IN DUCTILE FRACTURE PERFORMANCE AND PROCESS FOR PRODUCING THEM

Document Type and Number:

WIPO Patent Application WO/2006/106591

Kind Code:

A1

Abstract:

A high-strength steel sheet and high-strength welded steel pipe excelling in ductile fracture performance that have a tensile strength corresponding to X100 class of API standards; and a process for producing them. There is provided a high-strength steel sheet excelling in ductile fracture performance characterized by being composed of, in terms of mass%, 0.01 to 0.5% C, 0.01 to 3% Si, 0.1 to 5% Mn, ≤0.03% P, ≤0.03% S and the balance of Fe and unavoidable impurities, and by having a microstructure wherein 1 to 60%, in terms of area ratio, of ferrite is contained with the balance composed of bainite and martensite, and characterized in that the maximum of degree of &lcub 100&rcub accumulation in section resulting from 20° to 50° rotation of through-thickness section on the rolling direction as an axis is ≤3, and that the through-thickness parallel crack measured by ultrasonic inspection method is < 1 mm. Further, there is provided a high-strength welded steel pipe produced from the high-strength steel sheet as a parent material.

Inventors:

HARA TAKUYA (JP)
SHINOHARA YASUHIRO (JP)
ASAHI HITOSHI (JP)
TERADA YOSHIO (JP)

Application Number:

PCT/JP2005/007756

Publication Date:

October 12, 2006

Filing Date:

April 19, 2005

Export Citation:

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Assignee:

NIPPON STEEL CORP (JP)
HARA TAKUYA (JP)
SHINOHARA YASUHIRO (JP)
ASAHI HITOSHI (JP)
TERADA YOSHIO (JP)

International Classes:

C22C38/00; B23K35/30; C21D8/10; C22C38/04; C22C38/58

Foreign References:

JPH11343542A	1999-12-14
JP2002285283A	2002-10-03
JP2003096517A	2003-04-03
JPH10147846A	1998-06-02
EP0757113A1	1997-02-05
EP1777316A1	2007-04-25
EP1020539A2	2000-07-19

Other References: