US 12,188,103 B2
High strength steel sheet and method for manufacturing the same
Kazuki Endoh, Tokyo (JP); Yoshiyasu Kawasaki, Tokyo (JP); and Yuki Toji, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/770,116
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Oct. 8, 2020, PCT No. PCT/JP2020/038195
§ 371(c)(1), (2) Date Apr. 19, 2022,
PCT Pub. No. WO2021/079753, PCT Pub. Date Apr. 29, 2021.
Claims priority of application No. 2019-192513 (JP), filed on Oct. 23, 2019.
Prior Publication US 2022/0267876 A1, Aug. 25, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (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 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/16 (2006.01); C22C 38/38 (2006.01); C22C 38/60 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (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 38/008 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/16 (2013.01); C22C 38/38 (2013.01); C22C 38/60 (2013.01); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01)] 18 Claims
 
1. A steel sheet comprising:
a chemical composition containing, by mass,
C: 0.030% or more and 0.250% or less,
Si: 0.01% or more and 3.00% or less,
Mn: 2.50% or more and 8.00% or less,
P: 0.001% or more and 0.100% or less,
S: 0.0001% or more and 0.0200% or less,
N: 0.0005% or more and 0.0100% or less, and
Al: 0.001% or more and 2.000% or less,
with the balance being Fe and incidental impurities;
a steel microstructure including, by area, ferrite: 30% or more and 80% or less, martensite: 5% or more and 35% or less, and retained austenite: 8% or more,
wherein a quotient of an area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by a total area fraction of the retained austenite is 0.3 or more,
wherein a quotient of an average Mn content (mass %) in the retained austenite divided by an average Mn content (mass %) in the ferrite is 1.5 or more, and a product of the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite and an average aspect ratio of the retained austenite is 3.0 or more,
wherein a quotient of an average C content (mass %) in the retained austenite divided by an average C content (mass %) in the ferrite is 3.0 or more, and
wherein a quotient of the average C content (mass %) in the retained austenite divided by the average Mn content (mass %) in the retained austenite is 0.05 or more.