	US 12,173,391 B2
	Steel sheet and plated steel sheet
Keitaro Matsuda, Tokyo (JP); Takuya Mitsunobu, Tokyo (JP); Masaaki Uranaka, Tokyo (JP); Jun Maki, Tokyo (JP); and Hiroshi Takebayashi, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/271,138
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Mar. 14, 2022, PCT No. PCT/JP2022/011394 § 371(c)(1), (2) Date Jul. 6, 2023, PCT Pub. No. WO2022/230400, PCT Pub. Date Nov. 3, 2022.
Claims priority of application No. 2021-075057 (JP), filed on Apr. 27, 2021.
Prior Publication US 2023/0399727 A1, Dec. 14, 2023
Int. Cl. C22C 38/38 (2006.01); C21D 1/84 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C21D 9/46 (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 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01); C23C 2/06 (2006.01); C23C 2/40 (2006.01)

CPC C22C 38/38 (2013.01) [C21D 1/84 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (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); C21D 8/0278 (2013.01); C21D 9/46 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C23C 2/06 (2013.01); C23C 2/40 (2013.01)]

6 Claims

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

C: 0.05 to 0.40%,

Si: 0.2 to 3.0%,

Mn: 0.1 to 5.0%,

sol. Al: 0.4 to 1.50%,

P: 0.0300% or less,

S: 0.0300% or less,

N: 0.0100% or less,

B: 0 to 0.010%,

Ti: 0 to 0.150%,

Nb: 0 to 0.150%,

V: 0 to 0.150%,

Cr: 0 to 2.00%,

Ni: 0 to 2.00%,

Cu: 0 to 2.00%,

Mo: 0 to 1.00%,

W: 0 to 1.00%,

Ca: 0 to 0.100%,

Mg: 0 to 0.100%,

Zr: 0 to 0.100%,

Hf: 0 to 0.100%, and

REM: 0 to 0.100% and

having a balance of Fe and impurities, in which steel sheet,

an internal oxidation layer including fine granular oxides, coarse granular oxides, and grain boundary oxides is present in a surface layer of the steel sheet, and,

when examining a cross-section of a surface layer of the steel sheet,

a number density of fine granular oxides in the internal oxidation layer is 4.0/μm²or more,

a number density of coarse granular oxides in the internal oxidation layer is 4.0/25 μm²or more, and

a Ratio A of the length of the grain boundary oxides projected on the surface of the steel sheet to the length of the surface of the steel sheet is 50% or more and 100% or less, and

a surface depleted layer with a steel composition not including the fine granular oxides, coarse granular oxides, and grain boundary oxides which satisfies, by mass %, Si≤0.6% and Al≥0.05% is included at a depth of ½ of the average depth of the internal oxidation layer.