US 12,077,832 B2
Steel sheet
Yuya Suzuki, Tokyo (JP); and Kengo Takeda, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/025,862
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Sep. 28, 2021, PCT No. PCT/JP2021/035603
§ 371(c)(1), (2) Date Mar. 10, 2023,
PCT Pub. No. WO2022/071305, PCT Pub. Date Apr. 7, 2022.
Claims priority of application No. 2020-164884 (JP), filed on Sep. 30, 2020.
Prior Publication US 2023/0349022 A1, Nov. 2, 2023
Int. Cl. C21D 9/46 (2006.01); B22D 11/00 (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 38/10 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/20 (2006.01); C22C 38/22 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/30 (2006.01); C22C 38/34 (2006.01); C22C 38/38 (2006.01); C22C 38/42 (2006.01); C22C 38/48 (2006.01); C22C 38/58 (2006.01); C22C 38/60 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B22D 11/001 (2013.01); B32B 15/013 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (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); C21D 8/0263 (2013.01); C21D 8/0278 (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 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/105 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/30 (2013.01); C22C 38/34 (2013.01); C22C 38/38 (2013.01); C22C 38/42 (2013.01); C22C 38/48 (2013.01); C22C 38/58 (2013.01); C22C 38/60 (2013.01); C23C 2/28 (2013.01); C21D 2211/005 (2013.01); C21D 2211/009 (2013.01); C23C 2/40 (2013.01)] 4 Claims
OG exemplary drawing
 
1. A steel sheet comprising, as a chemical composition, by mass %:
C: 0.150% or more and 0.300% or less;
Si: 0.30% or more and 2.50% or less;
Mn: 1.50% or more and 4.00% or less;
Al: 0.30% or more and 2.00% or less;
P: 0% or more and 0.0400% or less;
S: 0% or more and 0.0100% or less;
N: 0.0025% or more and 0.0100% or less;
O: 0% or more and 0.0060% or less;
Cr: 0% or more and 0.500% or less;
Ni: 0% or more and 1.000% or less;
Cu: 0% or more and 1.000% or less;
Mo: 0% or more and 0.500% or less;
Ti: 0% or more and 0.200% or less;
Nb: 0% or more and 0.200% or less;
V: 0% or more and 0.500% or less;
B: 0% or more and 0.0100% or less;
W: 0% or more and 0.100% or less;
Ta: 0% or more and 0.100% 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 0.040% or less;
Y: 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;
Zr: 0% or more and 0.050% or less; and
a remainder comprising Fe and impurities,
wherein a metallographic structure at a ¼ thickness portion includes, by a volume percentage, a total of 50% or more of one or both of martensite and bainite and 8% or more of residual austenite, and a remainder being one or both of ferrite and pearlite,
an average value of aspect ratios of prior austenite grains is 5.0 or more at the ¼ thickness portion,
a number density of AlN is 3000 pieces/mm2 or more and less than 6000 pieces/mm2 at a depth position of 30 μm from a sheet surface,
an internal oxidation layer in which at least a part of a crystal grain boundary is coated with an oxide is provided from the sheet surface to a depth of 5.0 μm or more,
a grain boundary coverage of the oxide is 60% or more in a region from the sheet surface to a depth of 5.0 μm, the grain boundary coverage being a ratio of the length of the crystal grain boundary coated with the oxide to the total length if the crystal grain boundary in the region from the sheet surface to a depth of 5.0 μm, and
a tensile strength is 980 MPa or more.