US 12,467,110 B2
High strength steel sheet, high strength coated or plated steel sheet, methods of producing same, and member
Hidekazu Minami, Tokyo (JP); Yusuke Wada, Tokyo (JP); Yuki Toji, Tokyo (JP); Takeshi Nishiyama, Tokyo (JP); and Michitoshi Saeki, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/572,182
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed May 31, 2022, PCT No. PCT/JP2022/022198
§ 371(c)(1), (2) Date Dec. 20, 2023,
PCT Pub. No. WO2023/281939, PCT Pub. Date Jan. 12, 2023.
Claims priority of application No. 2021-114595 (JP), filed on Jul. 9, 2021.
Prior Publication US 2024/0287637 A1, Aug. 29, 2024
Int. Cl. C21D 9/46 (2006.01); C21D 1/18 (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 38/08 (2006.01); C22C 38/10 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C22C 38/38 (2006.01); C22C 38/60 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 1/18 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (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 38/08 (2013.01); C22C 38/10 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/38 (2013.01); C22C 38/60 (2013.01); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A high strength steel sheet comprising a chemical composition containing, in mass %,
C: 0.090% or more and 0.390% or less,
Si: 0.01% or more and 2.50% or less,
Mn: 2.00% or more and 4.00% or less,
P: 0.100% or less,
S: 0.0200% or less,
Al: 0.100% or less,
N: 0.0100% or less,
Nb: 0.002% or more and 0.100% or less,
Ti: 0.005% or more and 0.100% or less, and
B: 0.0002% or more and 0.0100% or less, wherein
[% Si]/[% Mn] is 0.10 or more and 0.60 or less, and
free Ti content determined from Formula (1), below, is 0.001 mass % or more,
with the balance being Fe and inevitable impurity, wherein
in a steel sheet surface layer, up to 100 μm from the surface of the steel sheet, a total amount of Nb solute and Nb precipitate having a diameter of 100 nm or smaller is 0.002 mass % or more with respect to the mass of the steel sheet surface layer,
the steel microstructure at a ¼ sheet thickness position comprising:
area ratio of martensite: 78% or more,
area ratio of ferrite: 10% or less,
volume fraction of retained austenite: less than 10.0%, wherein
an average value of a ratio of grain size in the rolling direction to grain size in the thickness direction of prior austenite grains is 2.0 or less, wherein the average value of ratio is obtained by averaging the ratios of the grain size in the rolling direction to the grain size in the thickness direction of prior austenite grains in three 169 μm×225 μm views taken of a thickness cross section, parallel to the rolling direction, of the steel sheet,
hardness variation frequency is 20 or less per 1500 μm in the sheet transverse direction at a 200 μm sheet thickness position, wherein the hardness is Vickers hardness measured with a 50 gf load, and the hardness variation frequency is determined by counting, in a 1500 μm length at 15 μm intervals, the number of times the hardness varies up or down by at least (Hvmax−Hvmin)/2, where Hvmax is the maximum hardness value over the 1500 μm length and Hvmin is the minimum hardness value over the 1500 μm length, and
tensile strength of the steel sheet is 1180 MPa or more,

OG Complex Work Unit Math
where [% X] in Formula (1) represents content of element X in the steel in mass %, and is 0 when not present.