US 12,258,645 B2
High-strength steel sheet and method for producing the same
Takuya Hirashima, Tokyo (JP); Yuma Honda, Tokyo (JP); Akinori Nakamura, Tokyo (JP); and Shinjiro Kaneko, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/426,897
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Dec. 19, 2019, PCT No. PCT/JP2019/049749
§ 371(c)(1), (2) Date Jul. 29, 2021,
PCT Pub. No. WO2020/158228, PCT Pub. Date Aug. 6, 2020.
Claims priority of application No. 2019-012790 (JP), filed on Jan. 29, 2019.
Prior Publication US 2022/0098698 A1, Mar. 31, 2022
Int. Cl. C21D 9/46 (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 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C22C 38/42 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0263 (2013.01); C21D 8/0273 (2013.01); C21D 8/0284 (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); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/42 (2013.01); C23C 2/02 (2013.01); C23C 2/022 (2022.08); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/29 (2022.08); C23C 2/40 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 24 Claims
 
1. A high-strength steel sheet having a chemical composition comprising, by mass %,
C: 0.06% or greater and 0.120% or less;
Si: 0.3% or greater and 0.7% or less;
Mn: 1.6% or greater and 2.2% or less;
P: 0.05% or less;
S: 0.0050% or less;
Al: 0.01% or greater and 0.20% or less;
and N: 0.010% or less; and
a balance being Fe and incidental impurities,
wherein the steel sheet has a microstructure in which ferrite is present as a major phase, and martensite is present in an area fraction in a range of 10% or greater and less than 50% relative to an entire area of the microstructure,
the martensite has an average grain diameter of 3.0 μm or less,
in an entirety of the martensite, a proportion of martensite having an aspect ratio of 3 or less is 60% or greater,
the martensite having an aspect ratio of 3 or less has a carbon concentration in a range of 0.30% or greater and 0.90% or less, by mass %,
the high-strength steel sheet is a steel sheet with a tensile strength of 590 MPa or greater, and
the high-strength steel sheet has a yield ratio of 0.63 or less, where the yield ratio is yield strength in MPa over tensile strength in MPa.