	US 12,473,622 B2
	Steel sheet, method for manufacturing same and plated steel sheet
Mitsuru Yoshida, Tokyo (JP); and Nobusato Kojima, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/297,697
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Mar. 3, 2020, PCT No. PCT/JP2020/008888 § 371(c)(1), (2) Date May 27, 2021, PCT Pub. No. WO2020/195605, PCT Pub. Date Oct. 1, 2020.
Claims priority of application No. 2019-059420 (JP), filed on Mar. 26, 2019.
Prior Publication US 2022/0025499 A1, Jan. 27, 2022
Int. Cl. C22C 38/58 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/54 (2006.01); C23C 2/02 (2006.01)

CPC C22C 38/58 (2013.01) [C21D 8/0226 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/54 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C21D 2211/009 (2013.01)]

10 Claims

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

C: 0.02% to 0.15%,

Si: 0.005% to 2.000%,

Mn: 1.00% to 3.00%,

Ti: 0.010% to 0.200%,

sol. Al: 0.001% to 1.000%,

N: 0.0010% to 0.0100%,

P: 0.100% or less,

S: 0.0100% or less,

Nb: 0% to 0.100%,

V: 0% to 0.500%,

Mo: 0% to 0.500%,

Cu: 0% to 1.00%,

Ni: 0% to 1.00%,

Cr: 0% to 2.00%,

B: 0% to 0.0020%,

Ca: 0% to 0.0100%,

Mg: 0% to 0.0100%,

REM: 0% to 0.0100%, and

Bi: 0% to 0.0200%

with a remainder comprising Fe and an impurity,

wherein, at a ¼ depth position of a sheet thickness from a surface, a total area fraction of tempered martensite and tempered bainite is 10% or more and 79% or less, an area fraction of ferrite is 21% or more and 90% or less, an area fraction of residual austenite is 0% or more and less than 4%, a total area fraction of the residual austenite, fresh martensite, cementite, and pearlite is 0% or more and 10% or less,

an average grain size is 15.0 μm or less,

a total grain boundary number density of solute C and solute B is 1.0 solute/nm²or more and 12.0 solutes/nm²or less,

a total of pole densities of {211}<011> and {332}<113> in a thickness middle portion is 12.0 or less, and

a tensile strength is 780 MPa or more.