US 12,344,912 B2
Steel sheet and manufacturing method thereof
Yuya Suzuki, Tokyo (JP); and Kengo Takeda, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/792,112
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Jan. 12, 2021, PCT No. PCT/JP2021/000703
§ 371(c)(1), (2) Date Jul. 11, 2022,
PCT Pub. No. WO2021/145310, PCT Pub. Date Jul. 22, 2021.
Claims priority of application No. 2020-003677 (JP), filed on Jan. 14, 2020.
Prior Publication US 2023/0059951 A1, Feb. 23, 2023
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/20 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/30 (2006.01); C22C 38/32 (2006.01); C22C 38/44 (2006.01); C22C 38/58 (2006.01); C23C 2/02 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/007 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/008 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/20 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/30 (2013.01); C22C 38/32 (2013.01); C22C 38/44 (2013.01); C22C 38/58 (2013.01); C23C 2/022 (2022.08); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 16 Claims
OG exemplary drawing
 
1. A steel sheet comprising, as a chemical composition, in mass %,
C: 0.050% or more and 0.500% or less,
Si: 0.01% or more and 2.50% or less,
Mn+Cr: 1.20% or more and 4.00% or less,
Al: 0.10% or more and 2.00% or less,
P: 0% or more and 0.100% or less,
S: 0% or more and 0.050% or less,
N: 0% or more and 0.010% or less,
O: 0% or more and 0.006% or less,
Mo: 0% or more and 1.000% or less,
Ti: 0% or more and 0.200% or less,
Nb: 0% or more and 0.200% or less,
B: 0% or more and 0.010% or less,
V: 0% or more and 0.200% or less,
Cu: 0% or more and 1.000% or less,
W: 0% or more and 0.100% or less,
Ta: 0% or more and 0.100% or less,
Ni: 0% or more and 1.000% or less,
Sn: 0% or more and 0.050% or less,
Co: 0% or more and 0.500% or less,
Sb: 0% or more and 0.050% or less,
As: 0% or more and 0.050% or less,
Mg: 0% or more and 0.050% or less,
Ca: 0% or more and 0.050% or less,
Y: 0% or more and 0.050% or less,
Zr: 0% or more and 0.050% or less,
La: 0% or more and 0.050% or less,
Ce: 0% or more and 0.050% or less, and
a remainder consisting of Fe and impurities,
wherein a metallographic structure at a position of ¼ of a sheet thickness from a surface includes, in volume percentage,
ferrite and epitaxial ferrite: 10% or more and less than 50%,
a proportion of the epitaxial ferrite in a total volume percentage of the ferrite and the epitaxial ferrite: 5% or more and 30% or less,
martensite: 20% or more and 70% or less,
bainite: 50% or less,
residual austenite: 15% or less, and
a remainder in microstructure: 5% or less,
a total volume percentage of the bainite, the residual austenite and the remainder in microstructure is 50% or less,
A/B, which is a ratio of a length A of an interface between the epitaxial ferrite and the ferrite to a length B of an interface between the epitaxial ferrite and the martensite in a cross section that is along a rolling direction and perpendicular to the surface at the position of ¼ of the sheet thickness from the surface, is more than 1.5,
a ratio of a major axis to a minor axis of the martensite is 5.0 or more, and
a tensile strength is 980 MPa or more.