	US 12,084,740 B2
	Steel sheet
Yuya Suzuki, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/432,330
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 24, 2020, PCT No. PCT/JP2020/017825 § 371(c)(1), (2) Date Aug. 19, 2021, PCT Pub. No. WO2020/218572, PCT Pub. Date Oct. 29, 2020.
Claims priority of application No. 2019-083400 (JP), filed on Apr. 24, 2019.
Prior Publication US 2022/0170127 A1, Jun. 2, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (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 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/60 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)

CPC C21D 9/46 (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 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/60 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01)]

4 Claims

1. A steel sheet with a tensile strength of 780 MPa or more,

a region down to 30 μm from a surface of the steel sheet in a sheet thickness direction being defined as a “surface layer part”,

at the surface layer part of at least one side,

particle size 20 nm or more Al oxide grains being present in 3000 to 6000/mm²in number density,

an average of natural logarithms of the particle sizes of the Al oxide grains measured in μm units being −5.0 to −3.5,

a standard error of the natural logarithms of the particle sizes being 0.8 or less,

a number of Al oxide grains with deviations of the natural logarithms of the particle sizes from the average of larger than 2 times the standard error being 5% or less of the total number of Al oxide grains,

a chemical composition at a position of ¼ of the thickness from the surface of the steel sheet comprising, by mass %,

C: 0.050 to 0.800%,

Si: 0.01 to 1.20%,

Mn: 0.01 to 8.00%,

P: 0.100% or less,

S: 0.050% or less,

Al: 0 to 3.000%,

N: 0.010% or less,

O: 0 to 0.020%,

Cr: 0 to 3.00%,

Mo: 0 to 1.00%,

B: 0 to 0.0100%,

Ti: 0 to 0.200%,

Nb: 0 to 0.200%,

V: 0 to 0.20%,

Cu: 0 to 1.000%,

Ni: 0 to 1.000%, and

bal.: Fe and impurities,

a number density of Al oxide grains at a position of ½ of the thickness of the steel sheet being 1000/mm²or less.