US 12,492,456 B2
Ultra high strength and high ductility steel sheet having excellent yield ratio and manufacturing method for same
Joo-Hyun Ryu, Gwangyang-si (KR); Kyoo-Young Lee, Gwangyang-si (KR); and Sea-Woong Lee, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 17/272,859
Filed by POSCO, Pohang-si (KR)
PCT Filed Sep. 3, 2019, PCT No. PCT/KR2019/011281
§ 371(c)(1), (2) Date Mar. 2, 2021,
PCT Pub. No. WO2020/050573, PCT Pub. Date Mar. 12, 2020.
Claims priority of application No. 10-2018-0105634 (KR), filed on Sep. 4, 2018.
Prior Publication US 2021/0317554 A1, Oct. 14, 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); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C23C 2/02 (2006.01); C23C 2/28 (2006.01)
CPC C22C 38/50 (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 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/28 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 4 Claims
 
1. A steel sheet comprising, in wt %:
0.1% to 0.3% of carbon (C), 2% or less of silicon (Si), 7-10% of manganese (Mn), 0.05% or less of phosphorus (P), 0.02% or less of sulfur(S), 0.02% or less of nitrogen (N), 0.5% or less excluding 0% of aluminum (Al), one or more selected from the group consisting of 0.1% or less of titanium (Ti), 0.1% or less of niobium (Nb), 0.2% or less of vanadium (V), and 0.5% or less of molybdenum (Mo), and a balance Fe and inevitable impurities;
a microstructure comprising: 20 area % or more of retained austenite, wherein grains of the retained austenite have an average aspect ratio being 2.0 or higher;
a tensile strength of 1,400 MPa or greater, a yield ratio of 0.7 or greater, and a product of tensile strength and elongation (TS*EL) of 22,000 MPa % or greater.