US 12,286,680 B2
Thin steel sheet and method for manufacturing same
Noriaki Kohsaka, Tokyo (JP); Junya Tobata, Tokyo (JP); Shinjiro Kaneko, Tokyo (JP); Yasushi Kitani, Tokyo (JP); Yoshihiko Ono, Tokyo (JP); and Tadachika Chiba, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/284,981
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Oct. 15, 2019, PCT No. PCT/JP2019/040400
§ 371(c)(1), (2) Date Apr. 13, 2021,
PCT Pub. No. WO2020/080339, PCT Pub. Date Apr. 23, 2020.
Claims priority of application No. 2018-195602 (JP), filed on Oct. 17, 2018.
Prior Publication US 2021/0381077 A1, Dec. 9, 2021
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)
CPC C21D 9/46 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0273 (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); C21D 2201/05 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 4 Claims
OG exemplary drawing
 
1. A steel sheet comprising:
a chemical composition containing, in mass %,
C: 0.10% or more and 0.23% or less;
Si: 1.30% or more and 2.20% or less;
Mn: 2.0% or more and 3.2% or less;
P: 0.05% or less;
S: 0.005% or less;
Al: 0.005% or more and 0.100% or less; and
N: 0.0060% or less, the balance being Fe and incidental impurities; and
a microstructure including ferrite with an area fraction of 4% or less (including 0%), as-quenched martensite with an area fraction of 10% or less (including 0%), retained austenite with an amount of 7% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite with a total area fraction of more than 71% and less than 93%, wherein:
BCC iron having a misorientation of 1° or less and surrounds retained austenite having an equivalent circular diameter of 1 μm or less is present with an area fraction of 5% or more and 50% or less; and
BCC iron having a misorientation of more than 1° is present with an area fraction of 25% or more and 85% or less.