	US 12,247,263 B2
	Steel sheet and method for producing same
Kohichi Sano, Tokyo (JP); and Hiroyuki Kawata, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/432,016
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 8, 2020, PCT No. PCT/JP2020/015768 § 371(c)(1), (2) Date Aug. 18, 2021, PCT Pub. No. WO2020/209276, PCT Pub. Date Oct. 15, 2020.
Claims priority of application No. 2019-075693 (JP), filed on Apr. 11, 2019.
Prior Publication US 2022/0119909 A1, Apr. 21, 2022
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 38/38 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)

CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 6/004 (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); C21D 8/0263 (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 38/38 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/024 (2022.08); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/29 (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); C21D 2211/009 (2013.01)]

9 Claims

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

C: 0.040% to 0.400%;

Si: 0.01% to 2.50%;

Mn: 0.10% to 4.00%;

Al: 0.010% to 1.500%;

P: 0.001% to 0.100%;

S: 0.0005% to 0.0100%;

N: 0.0005% to 0.0100%;

Ti: 0% to 0.200%;

Mo: 0% to 0.300%;

Nb: 0% to 0.200%;

Cr: 0% to 4.00%;

B: 0% to 0.0050%;

V: 0% to 0.300%;

Ni: 0% to 4.00%;

Cu: 0% to 4.00%;

W: 0% to 2.00%;

Ca: 0% to 0.0100%;

Ce: 0% to 0.0100%;

Mg: 0% to 0.0100%;

Zr: 0% to 0.0100%;

La: 0% to 0.0100%;

REM other than Ce and La: 0% to 0.0100%;

Sn: 0% to 1.000%;

Sb: 0% to 0.200%; and

a remainder: Fe and impurities,

wherein a microstructure in a range from a ⅛ thickness position in a sheet thickness direction from a surface of the steel sheet to a ⅜ thickness position in the sheet thickness direction from the surface includes, by area fraction,

ferrite: 10% to 97%,

residual austenite and martensite: 3% to 90%,

bainite: 0% to 87%, and

pearlite: 0% to 10%,

in a plane parallel to a rolling direction at a ¼ thickness position in the sheet thickness direction from the surface, when a maximum value of Mn contents in a measurement range is indicated as Mn_max, an average value of the Mn contents is indicated as Mn_ave, regions where the Mn content is (Mn_ave+Mn_max)/2 or more are indicated as high Mn regions, and the other regions are indicated as low Mn regions,

an average distance between centers of the high Mn regions adjacent to each other is 1.00 mm or less,

a density D_Aof the high Mn regions at a sheet width center portion and a density D_Bof the high Mn regions at a ¼ width position from a sheet width end portion satisfy Expression (1),

a ratio of an average hardness of the high Mn regions to an average hardness of the low Mn regions is 1.1 to 2.0, and

a difference between an average of a top 5% and an average of a bottom 5% of the Mn contents at measurement points in the low Mn regions is 0.3 mass % or more,

0.77≤D_A/D_B≤1.30 Expression (1).