Invention Application
US20070071997A1 A COLD-ROLLED STEEL SHEET HAVING A TENSILE STRENGTH OF 780 MPA OR MORE, AN EXCELLENT LOCAL FORMABILITY AND A SUPPRESSED INCREASE IN WELD HARDNESS
有权
具有780 MPA或更高的拉伸强度的冷轧钢板,在焊接硬度方面具有优异的局部可制造性和抑制性增加
- Patent Title: A COLD-ROLLED STEEL SHEET HAVING A TENSILE STRENGTH OF 780 MPA OR MORE, AN EXCELLENT LOCAL FORMABILITY AND A SUPPRESSED INCREASE IN WELD HARDNESS
- Patent Title (中): 具有780 MPA或更高的拉伸强度的冷轧钢板,在焊接硬度方面具有优异的局部可制造性和抑制性增加
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Application No.: US10557263Application Date: 2004-01-09
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Publication No.: US20070071997A1Publication Date: 2007-03-29
- Inventor: Koichi Goto , Riki Okamoto , Hirokazu Taniguchi
- Applicant: Koichi Goto , Riki Okamoto , Hirokazu Taniguchi
- Priority: JP2003-143638 20030521
- International Application: PCT/JP04/00126 WO 20040109
- Main IPC: C22C38/00
- IPC: C22C38/00 ; B32B15/18

Abstract:
The present invention provides a high-strength cold-rolled steel sheet and a high-strength surface treated steel sheet 780 MPa or more in tensile strength, said steel sheets having excellent local formability and suppressed weld hardness increase and being characterized by: said steel sheets containing, in weight, C: 0.05 to 0.09%, Si: 0.4 to 1.3%, Mn: 2.5 to 3.2%, P: 0.001 to 0.05%, N: 0.0005 to 0.006%, Al: 0.005 to 0.1%, Ti: 0.001 to 0.045%, and S in the range stipulated by the following expression (A), with the balance consisting of Fe and unavoidable impurities; the microstructures of said steel sheets being composed of bainite of 7% or more in terms of area percentage and the balance consisting of one or more of ferrite, martensite, tempered martensite and retained austenite; and said components in said steel sheets satisfying the following expressions (C) and (D) when Mneq. is defined by the following expression (B); S≦0.08×(Ti(%)−3.43×N(%)+0.004 . . . (A), where, when a value of the member Ti(%)−3.43×N(%) of said expression (A) is negative, the value is regarded as zero. MIneq.=Mn(%)−0.29 ×Si(%)+6.24×C(%) . . . (B), 950≦(Mneq./(C(%)−(Si(%)/75)))×bainite area percentage (%) . . . (C), C(%)+(Si(%)/20)+(Mn(%)/18)50.30 . . . (D).
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