HIGH-STRENGTH STEEL SHEET OF 450 MPa OR HIGHER YIELD STRESS AND 570 MPa OR HIGHER TENSILE STRENGTH HAVING LOW ACOUSTIC ANISOTROPY AND HIGH WELDABILITY AND PROCESS FOR PRODUCING THE SAME

Title:

HIGH-STRENGTH STEEL SHEET OF 450 MPa OR HIGHER YIELD STRESS AND 570 MPa OR HIGHER TENSILE STRENGTH HAVING LOW ACOUSTIC ANISOTROPY AND HIGH WELDABILITY AND PROCESS FOR PRODUCING THE SAME

Document Type and Number:

WIPO Patent Application WO/2007/055387

Kind Code:

A1

Abstract:

A high-strength steel sheet of 450 MPa or higher yield stress and 570 MPa or higher tensile strength having low acoustic anisotropy and high weldability; and a process for producing the same. The Si content of steel is less than 0.10%, and the volume ratio of island martensite is less than 3%. Nb and Ti are contained so as to satisfy the relationships Nb≥0.025%, Ti≥0.005% and 0.045%≤Nb+2×Ti≤0.105%. Nb, Ti, C and N are contained in such amounts that the value of A=(Nb+2Ti)×(C+N×12/14) is in the range of 0.0022 to 0.0055. In the steel structure, the volume ratio of bainite is 30% or more while the volume ratio of pearlite is less than 5%.

Inventors:

HOSHINO MANABU (JP)
FUJIOKA MASAAKI (JP)
TANAKA YOUICHI (JP)
KUMAGAI TATSUYA (JP)

Application Number:

PCT/JP2006/322683

Publication Date:

May 18, 2007

Filing Date:

November 08, 2006

Export Citation:

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Assignee:

NIPPON STEEL CORP (JP)
HOSHINO MANABU (JP)
FUJIOKA MASAAKI (JP)
TANAKA YOUICHI (JP)
KUMAGAI TATSUYA (JP)

International Classes:

C22C38/00; B21B1/26; B21B3/00; C21D8/02; C22C38/14; C22C38/58

Foreign References:

JP2005126819A	2005-05-19
JP2002105590A	2002-04-10
JP2000219934A	2000-08-08
JP2000256777A	2000-09-19

Other References: