US 12,123,069 B2
Steel sheet and method for producing the same
Yoshihiko Ono, Tokyo (JP); Junya Tobata, Tokyo (JP); Hiroyuki Akimoto, Tokyo (JP); Yoichiro Matsui, Tokyo (JP); and Shinjiro Kaneko, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/286,148
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Oct. 16, 2019, PCT No. PCT/JP2019/040663
§ 371(c)(1), (2) Date Apr. 16, 2021,
PCT Pub. No. WO2020/080402, PCT Pub. Date Apr. 23, 2020.
Claims priority of application No. 2018-196150 (JP), filed on Oct. 17, 2018; and application No. 2019-165438 (JP), filed on Sep. 11, 2019.
Prior Publication US 2021/0355559 A1, Nov. 18, 2021
Int. Cl. C21D 9/46 (2006.01); C21D 1/20 (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 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01); C22C 38/60 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 1/20 (2013.01); C21D 6/004 (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); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (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 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C22C 38/60 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A steel sheet having a chemical composition comprising, by mass %:
C: 0.06% to 0.25%;
Si: 0.6% to 2.5%;
Mn: 2.3% to 3.5%;
P: 0.02% or less;
S: 0.01% or less;
sol. Al: less than 0.50%;
N: less than 0.015%; and
the balance being Fe and incidental impurities,
wherein the steel sheet has a steel microstructure comprising ferrite: 5% or less by area percentage, at least one of upper bainite, fresh martensite, tempered martensite, lower bainite, and retained γ: in a range of 95% to 100% by area percentage, and retained γ: in a range of 4% to 15% by volume percentage,
retained γUB with a grain width in a range of 0.25 to 0.60 μm, a grain length in a range of 1.0 to 15 μm, and an aspect ratio in a range of 3.1 to 25 has an area percentage SγUB in a range of 0.2% to 7.0%,
retained γLB with a grain width in a range of 0.08 to 0.24 μm, a grain length in a range of 0.6 to 15 μm, and an aspect ratio in a range of 4 to 40 has a distribution number NγLB in a range of 10 to 120 per 100 μm2,
at least one of (i) fresh martensite with an equivalent circular grain diameter in a range of 0.4 to 1.0 μm and an aspect ratio of 3 or less and (ii) retained γ grains with an equivalent circular grain diameter in a range of 0.4 to 1.0 μm and an aspect ratio of 3 or less have a total area percentage SγFine in a range of 0.4% to 5.0%, and
at least one of (i) fresh martensite with an equivalent circular grain diameter in a range of 1.2 to 20 μm and an aspect ratio of 3 or less and (ii) retained γgrains with an equivalent circular grain diameter in a range of 1.2 to 20 μm and an aspect ratio of 3 or less have a total area percentage SγBlock in a range of 4% or less, including 0%.