	US 11,859,260 B2
	Steel sheet and manufacturing method thereof
Masahiro Kubo, Tokyo (JP); Hiroyuki Kawata, Tokyo (JP); Masahiro Saito, Tokyo (JP); Kenichiro Otsuka, Tokyo (JP); and Masafumi Azuma, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/419,557
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Jan. 7, 2020, PCT No. PCT/JP2020/000139 § 371(c)(1), (2) Date Jun. 29, 2021, PCT Pub. No. WO2020/145259, PCT Pub. Date Jul. 16, 2020.
Claims priority of application No. 2019-000671 (JP), filed on Jan. 7, 2019.
Prior Publication US 2022/0074015 A1, Mar. 10, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/44 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01); C21D 6/00 (2006.01); C21D 1/18 (2006.01); C21D 8/02 (2006.01)

CPC C21D 9/46 (2013.01) [B32B 15/01 (2013.01); C21D 1/18 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (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 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/44 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C21D 2211/005 (2013.01)]

9 Claims

1. A steel sheet comprising, as a chemical composition, by mass %:

C: 0.050% to 0.145%;

Mn: 0.70% to 2.25%;

Al and Si in total: 0.60% or less;

P: 0 to 0.030%;

S: 0 to 0.020%;

N: 0 to 0.0050%;

Mo: 0% to 0.80%;

B: 0% to 0.0050%;

Ti: 0% to 0.200%;

Nb: 0% to 0.100%;

Cr: 0% to 0.700%;

Ni: 0% to 0.200%; and

a remainder of iron and impurities,

wherein a metallographic structure in a surface layer region ranging from a surface to a position of 20 μm from the surface in a sheet thickness direction consists of ferrite and a secondary phase having a volume fraction of 1.0% to 15.0%,

a metallographic structure in an internal region ranging from a position of more than 20 μm from the surface in the sheet thickness direction to a ¼ thickness position from the surface in the sheet thickness direction consists of ferrite and a secondary phase having a volume fraction of 5.0% to 25.0%,

the volume fraction of the secondary phase in the surface layer region is less than the volume fraction of the secondary phase in the internal region, and

in the surface layer region,

an average grain size of the secondary phase is 0.5 μm to 4.0 μm, and

a texture in which an X_{ODF{001}/{111}} as a ratio of an intensity of {001} orientation to an intensity of {111} orientation in the ferrite is 0.70 to 2.50 is included,

wherein an average grain size of the secondary phase in the internal region is 1.0 μm to 5.0 μm and is more than the average grain size of the secondary phase in the surface layer region, and

wherein the chemical composition satisfies following Expression (1),

a tensile strength is 550 MPa or higher,

a sheet thickness is 0.10 mm to 0.55 mm, and

a sheet width is 1300 mm to 2000 mm,

7.00≥[C]×20+[Si]×3.0+[Mn]×2.0+[Al]×2.0+[Cr]+[Ti]×20+[Nb]×40+[Mo]×2.0+[Ni]×2.0+[B]×200 (1),

where a symbol of each of the elements in Expression (1) represents an amount of the element by mass %, and when the element is not included, 0 is substituted into the symbol.