	US 11,739,392 B2
	High-strength steel sheet and method for manufacturing the same
Yusuke Kimata, Tokyo (JP); Yoshihiko Ono, Tokyo (JP); and Kenji Kawamura, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 16/76,374
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Feb. 7, 2017, PCT No. PCT/JP2017/004310 § 371(c)(1), (2) Date Aug. 8, 2018, PCT Pub. No. WO2017/138503, PCT Pub. Date Aug. 17, 2017.
Claims priority of application No. 2016-023453 (JP), filed on Feb. 10, 2016; and application No. 2016-235854 (JP), filed on Dec. 5, 2016.
Prior Publication US 2019/0040482 A1, Feb. 7, 2019
Int. Cl. C21D 8/02 (2006.01); C21D 9/46 (2006.01); C22C 38/06 (2006.01); C22C 38/16 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C21D 6/00 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01)

CPC C21D 8/0247 (2013.01) [C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); 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); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)]

12 Claims

1. A high-strength steel sheet having a chemical composition comprising:

C: more than 0.30% and 0.40% or less, by mass %;

Si: 0.5% or more and 2.5% or less, by mass %;

Mn: 3.8% or more and 5.0% or less, by mass %;

P: 0.1% or less, by mass %;

S: 0.01% or less, by mass %;

Al: 0.01% or more and 0.5% or less, by mass %;

N: 0.010% or less, by mass %; and

Fe and inevitable impurities,

wherein:

the steel sheet has a microstructure including, in terms of area fraction with respect to the whole steel sheet microstructure,

lower bainite in an amount of 40% or more and less than 85%,

martensite including tempered martensite in an amount of 5% or more and less than 40%,

retained austenite in an amount of 10% or more and 30% or less, and having an average crystal grain diameter in a range of 1.6 μm or more an 2.0 μm or less, and

polygonal ferrite in an amount of 10% or less (including 0%),

the steel sheet has

a tensile strength of 1320 MPa or more,

(tensile strength×total elongation) of 18000 MPa·% or more, and

(tensile strength×hole expansion ratio) of 40000 MPa·% or more.