US 12,331,374 B2
Thin steel sheet and method for manufacturing same
Noriaki Kohsaka, Tokyo (JP); Shinjiro Kaneko, Tokyo (JP); Akinori Nakamura, Tokyo (JP); Yuma Honda, Tokyo (JP); Tadachika Chiba, Tokyo (JP); and Yoshihiko Ono, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/284,534
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Oct. 15, 2019, PCT No. PCT/JP2019/040397
§ 371(c)(1), (2) Date Apr. 12, 2021,
PCT Pub. No. WO2020/080337, PCT Pub. Date Apr. 23, 2020.
Claims priority of application No. 2018-195601 (JP), filed on Oct. 17, 2018.
Prior Publication US 2021/0381076 A1, Dec. 9, 2021
Int. Cl. C21D 9/46 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/42 (2006.01); C22C 38/58 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0236 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/42 (2013.01); C22C 38/58 (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: 0.08% or more and 0.24% or less;
Si: 0.70% or more and 2.20% or less;
Mn: 0.8% or more and 1.86% or less;
P: 0.05% or less;
S: 0.005% or less;
Al: 0.005% or more and 0.70% or less; and
N: 0.0060% or less, the balance being Fe and incidental impurities; and
a microstructure including ferrite in an area fraction of 5% or more and 60% or less, as-quenched martensite in an area fraction of 10% or less (including 0%), retained austenite in an area fraction of 5% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite in a total area fraction of more than 15% and less than 85%, wherein:
BCC iron having a misorientation of 1° or less and surrounds retained austenite having an aspect ratio of 2.5 or higher is present in an area fraction of 5% or more and 70% or less; and
a top 10% of retained austenite in terms of an equivalent circular diameter, of all retained austenite surrounded by BCC iron having a misorientation of 1° or less, has an average aspect ratio of 2.5 or higher.