	US 12,139,772 B2
	High strength steel sheet
Genki Abukawa, Tokyo (JP); and Hiroshi Shuto, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/603,726
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Jul. 8, 2020, PCT No. PCT/JP2020/026717 § 371(c)(1), (2) Date Oct. 14, 2021, PCT Pub. No. WO2021/006298, PCT Pub. Date Jan. 14, 2021.
Claims priority of application No. 2019-128590 (JP), filed on Jul. 10, 2019.
Prior Publication US 2022/0195554 A1, Jun. 23, 2022
Int. Cl. 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)

CPC C21D 9/46 (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); C21D 2211/002 (2013.01); C21D 2211/008 (2013.01)]

8 Claims

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

C: 0.030% to 0.280%;

Si: 0.05% to 2.50%;

Mn: 1.00% to 4.00%;

sol. Al: 0.001% to 2.000%;

P: 0.100% or less;

S: 0.0200% or less;

N: 0.01000% or less;

O: 0.0100% or less;

Ti: 0% to 0.20%;

Nb: 0% to 0.20%;

total of Ti and Nb: 0.04% to 0.40%;

B: 0% to 0.010%;

V: 0% to 1.000%;

Cr: 0% to 1.000%;

Mo: 0% to 1.000%;

Cu: 0% to 1.000%;

Co: 0% to 1.000%;

W: 0% to 1.000%;

Ni: 0% to 1.000%;

Ca: 0% to 0.0100%;

Mg: 0% to 0.0100%;

REM: 0% to 0.0100%;

Zr: 0% to 0.0100%; and

a remainder including Fe and impurities,

wherein, in a metallographic structure, a total area ratio of tempered martensite and bainite is 80% or more,

at a sheet thickness ¼ position of a cross section parallel to a rolling direction and perpendicular to a rolled surface, a standard deviation of number densities of precipitates having a diameter of 10 nm or less and including one or both of Ti and Nb is less than 5×10¹⁰numbers/mm³, in which the number densities are measured at 10 points every 50 mm in a width direction, and

a tensile strength is 780 MPa or more.