	US 12,258,647 B2
	Steel sheet, member, and methods for manufacturing the same
Yusuke Wada, Tokyo (JP); Tatsuya Nakagaito, Tokyo (JP); Shotaro Terashima, Tokyo (JP); Lingling Yang, Tokyo (JP); and Takeshi Yokota, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/800,669
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Feb. 24, 2021, PCT No. PCT/JP2021/006715 § 371(c)(1), (2) Date Aug. 18, 2022, PCT Pub. No. WO2021/172298, PCT Pub. Date Sep. 2, 2021.
Claims priority of application No. 2020-033056 (JP), filed on Feb. 28, 2020.
Prior Publication US 2023/0349020 A1, Nov. 2, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (2006.01); C21D 1/18 (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 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01); C22C 38/34 (2006.01); C22C 38/38 (2006.01); C22C 38/60 (2006.01); C23C 2/06 (2006.01)

CPC C21D 9/46 (2013.01) [C21D 1/18 (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); 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 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C22C 38/34 (2013.01); C22C 38/38 (2013.01); C22C 38/60 (2013.01); C23C 2/06 (2013.01)]

17 Claims

1. A steel sheet comprising:

a chemical composition containing, by mass %,

C: 0.07% or more and 0.18% or less,

Si: 0.01% or more and 2.0% or less,

Al: 0.01% or more and 2.0% or less,

a total of Si and Al: 0.7% or more and 2.5% or less,

Mn: 1.5% or more and 2.6% or less,

P: 0.1% or less,

S: 0.02% or less, and

N: 0.010% or less, and

optionally containing at least one selected from Cr, V, Mo, Ni, and Cu in a total amount of 1.0% or less,

optionally containing at least one selected from

Ti: 0.20% or less, and

Nb: 0.20% or less,

optionally containing B: 0.005% or less,

optionally containing at least one selected from

Ca: 0.005% or less, and

REM: 0.005% or less, and

optionally containing at least one selected from

Sb: 0.05% or less, and

Sn: 0.05% or less,

with the balance being Fe and incidental impurities; and

a steel microstructure including, in terms of area fraction, ferrite: 40% or more and 70% or less, a total of bainite and tempered martensite: 5% or more and 30% or less, retained austenite: 4% or more and 18% or less, fresh martensite: 8% or more and 35% or less, and the remainder: 5% or less,

wherein cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less,

wherein the steel sheet has a tensile strength of 780 MPa or more and less than 980 MPa, and

wherein the cementite particles in the retained austenite have an average major axis of 30 nm or more and 400 nm or less.