	US 12,486,552 B2
	Steel sheet and method for manufacturing steel sheet
Arisa Ikeda, Tokyo (JP); and Kengo Takeda, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/927,107
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Aug. 16, 2021, PCT No. PCT/JP2021/029952 § 371(c)(1), (2) Date Nov. 22, 2022, PCT Pub. No. WO2022/070636, PCT Pub. Date Apr. 7, 2022.
Claims priority of application No. 2020-165790 (JP), filed on Sep. 30, 2020.
Prior Publication US 2023/0193415 A1, Jun. 22, 2023
Int. Cl. C21D 9/46 (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 38/10 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/22 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/30 (2006.01); C22C 38/34 (2006.01); C22C 38/38 (2006.01); C22C 38/42 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/60 (2006.01); C25D 3/44 (2006.01); C25D 5/36 (2006.01)

CPC C21D 9/46 (2013.01) [C21D 6/001 (2013.01); C21D 6/002 (2013.01); C21D 6/004 (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); 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 38/10 (2013.01); C22C 38/105 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/22 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/30 (2013.01); C22C 38/34 (2013.01); C22C 38/38 (2013.01); C22C 38/42 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/60 (2013.01); C25D 3/44 (2013.01); C25D 5/36 (2013.01); C21D 2211/008 (2013.01)]

7 Claims

1. A steel sheet comprising, as a chemical composition, in a unit of mass %:

C: 0.20% or more and 0.45% or less;

Si: 0.01% or more and 2.50% or less;

Mn: 1.20% or more and 3.50% or less;

P: 0.040% or less;

S: 0.010% or less;

Al: 0.001% or more and 0.100% or less;

N: 0.0001% or more and 0.0100% or less;

Ti: 0.005% or more and 0.100% or less;

B: 0% or more and 0.010% or less;

O: 0.006% or less;

Mo: 0% or more and 0.50% or less;

Nb: 0% or more and 0.20% or less;

Cr: 0% or more and 0.50% or less;

V: 0% or more and 0.50% or less;

Cu: 0% or more and 1.00% or less;

W: 0% or more and 0.100% or less;

Ta: 0% or more and 0.10% or less;

Ni: 0% or more and 1.00% or less;

Sn: 0% or more and 0.050% or less;

Co: 0% or more and 0.50% or less;

Sb: 0% or more and 0.050% or less;

As: 0% or more and 0.050% or less;

Mg: 0% or more and 0.050% or less;

Ca: 0% or more and 0.040% or less;

Y: 0% or more and 0.050% or less;

Zr: 0% or more and 0.050% or less;

La: 0% or more and 0.050% or less;

Ce: 0% or more and 0.050% or less; and

a remainder consisting of Fe and impurities,

wherein a Ti content and a N content satisfy the following formula 1,

at a sheet thickness ¼ position, a metallographic structure includes 90% or more of martensite in terms of volume fraction,

at the sheet thickness ¼ position, a number density of TiC having a circle equivalent diameter of 1 to 500 nm is 3.5×10⁴particles/mm²or more,

at the sheet thickness ¼ position, a value of a median value of a Mn concentration+3σ is 5.00% or less,

a hardness measured at the sheet thickness ¼ position is 1.30 times or more a hardness measured at a position 50 μm deep from a surface of the steel sheet, and

a tensile strength is 1310 MPa or more,

Ti−3.5×N≥0.003 (formula 1)

here, element symbols Ti and N in the formula 1 mean the Ti content and the N content of the steel sheet.