US 12,291,759 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. 17/781,658
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Dec. 17, 2020, PCT No. PCT/JP2020/047217
§ 371(c)(1), (2) Date Jun. 1, 2022,
PCT Pub. No. WO2021/125283, PCT Pub. Date Jun. 24, 2021.
Claims priority of application No. 2019-229401 (JP), filed on Dec. 19, 2019.
Prior Publication US 2023/0002846 A1, Jan. 5, 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 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/20 (2006.01); C22C 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0263 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01)] 12 Claims
OG exemplary drawing
 
1. A steel sheet,
wherein a chemical composition contains, by mass %,
C: 0.15% or more and 0.45% 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: 0.040% or less,
S: 0.010% or less,
N: 0.0010% or more and 0.010% or less,
O: 0.006% or less,
Mo: 0% or more and 0.50% or less,
Ti: 0% or more and 0.20% or less,
Nb: 0% or more and 0.20% or less,
B: 0% or more and 0.010% or less,
V: 0% or more and 0.50% or less,
Cu: 0% or more and 1.00% or less,
W: 0% or more and 0.10% or less,
Ta: 0% or more and 0.10% or less,
Ni: 0% or more and 1.00% or less,
Sn: 0% or more and 0.050% or less,
Co: 0% or more and 0.50% 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 0.040% 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 including Fe and an impurities,
a tensile strength is 1300 MPa or more,
a ratio (R/t) of a limit bend radius to a sheet thickness is less than 3.5,
when a depth position of 30 μm from a surface in a sheet thickness direction is defined as a position A and a depth position of ¼ of the sheet thickness from the surface in the sheet thickness direction is defined as a position B,
a number density of AlN at the position A is 3000 pieces/mm2 or more and 6000 pieces/mm2 or less,
a metallographic structure at the position B includes 90% or more of martensite by volume percentage, and
a hardness at the position A is 1.20 times or higher than a hardness at the position B.