Title:
STEEL SHEET
Document Type and Number:
WIPO Patent Application WO/2020/189530
Kind Code:
A1
Abstract:
A steel sheet having the following chemical composition in mass%: C: greater than 0.10% and less than 0.55%, Si: at least 0.001% and less than 3.50%, Mn: greater than 4.00% and less than 9.00%, sil.Al: at least 0.001% and less than 3.00%, P: not more than 0.100%, S: not more than 0.010%, N: less than 0.050%, O: less than 0.020%, Cr: at least 0% and less than 2.00%, Mo: 0 to 2.00%, W: 0 to 2.00%, Cu: 0 to 2.00%, Ni: 0 to 2.00%, Ti: 0 to 0.300%, Nb: 0 to 0.300%, V: 0 to 0.300%, B: 0 to 0.010%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, Zr: 0 to 0.010%, REM: 0 to 0.010%, Sb: 0 to 0.050%, Sn: 0 to 0.050%, Bi: 0 to 0.050%, and balance: Fe and impurities. In the L-cross section, at a position one-fourth of the thickness from the surface, the steel sheet has a metallographic composition, as an area ratio, of tempered martensite: 25 to 90%, ferrite: not more than 5%, retained austenite: 10 to 50%, and bainite: not more than 5%, wherein the area ratio of the total area of retained austenite crystal grains satisfying an area of at least 1 μm2 and a grain circularity of at least 0.1, to the total area of the retained austenite, is less than 50%. The steel sheet satisfies CMnγ/CMnα ≥ 1.2.
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Inventors:
SUWA YOSHIHIRO (JP)
HAYASHI KOUTAROU (JP)
OKAMOTO RIKI (JP)
KOHTAKE TAKAHIKO (JP)
HAYASHI KOUTAROU (JP)
OKAMOTO RIKI (JP)
KOHTAKE TAKAHIKO (JP)
Application Number:
PCT/JP2020/010946
Publication Date:
September 24, 2020
Filing Date:
March 12, 2020
Export Citation:
Assignee:
NIPPON STEEL CORP (JP)
International Classes:
C21D9/46; C22C38/00; C22C38/60
Domestic Patent References:
| WO2016067626A1 | 2016-05-06 |
Foreign References:
| JP2017053001A | 2017-03-16 | |||
| JP2016050337A | 2016-04-11 |
Attorney, Agent or Firm:
BRIGHTAS IP ATTORNEYS (JP)
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