US 11,655,517 B2
Ultrahigh-strength and high-ductility steel sheet having excellent cold formability
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. 16/761,953
Filed by POSCO CO., LTD, Pohang-si (KR)
PCT Filed Sep. 17, 2018, PCT No. PCT/KR2018/010907
§ 371(c)(1), (2) Date May 6, 2020,
PCT Pub. No. WO2019/093650, PCT Pub. Date May 16, 2019.
Claims priority of application No. 10-2017-0148175 (KR), filed on Nov. 8, 2017.
Prior Publication US 2021/0180150 A1, Jun. 17, 2021
This patent is subject to a terminal disclaimer.
Int. Cl. C23C 2/06 (2006.01); C23C 2/40 (2006.01); C22C 38/14 (2006.01); C22C 38/12 (2006.01); C22C 38/06 (2006.01); C22C 38/04 (2006.01); C22C 38/02 (2006.01); C22C 38/00 (2006.01); B32B 15/01 (2006.01); C21D 9/46 (2006.01); C21D 8/02 (2006.01); C21D 6/00 (2006.01); C23C 2/28 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C23C 30/00 (2006.01); B32B 15/04 (2006.01); B32B 15/18 (2006.01); C22C 38/18 (2006.01); C22C 38/24 (2006.01); C23C 28/02 (2006.01); C22C 38/42 (2006.01); C23C 2/26 (2006.01); C22C 38/50 (2006.01); C22C 38/20 (2006.01); C22C 38/46 (2006.01); C22C 38/38 (2006.01); C22C 38/44 (2006.01); C22C 38/22 (2006.01); C22C 38/40 (2006.01); C23C 2/12 (2006.01); C23C 28/00 (2006.01); C22C 38/48 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/01 (2013.01); B32B 15/012 (2013.01); B32B 15/013 (2013.01); B32B 15/04 (2013.01); B32B 15/043 (2013.01); B32B 15/18 (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); 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); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/18 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/38 (2013.01); C22C 38/40 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/26 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C23C 28/021 (2013.01); C23C 28/023 (2013.01); C23C 28/025 (2013.01); C23C 28/3225 (2013.01); C23C 30/00 (2013.01); C23C 30/005 (2013.01); C21D 2211/001 (2013.01); C21D 2211/004 (2013.01); C21D 2211/008 (2013.01); Y02P 10/20 (2015.11); Y10T 428/12757 (2015.01); Y10T 428/12799 (2015.01); Y10T 428/12951 (2015.01); Y10T 428/12958 (2015.01); Y10T 428/12965 (2015.01); Y10T 428/12972 (2015.01); Y10T 428/12979 (2015.01); Y10T 428/26 (2015.01)] 7 Claims
 
1. An ultrahigh-strength and high-ductility steel sheet having excellent cold formability, comprising, by weight percentage (wt %), carbon (C): 0.1% to 0.3%, manganese (Mn): 6% to 10%, phosphorus (P): 0.05% or less, sulfur (S): 0.02% or less, nitrogen (N): 0.02% or less, aluminum (Al): 0.5% or less (excluding 0%), at least one selected from the group consisting of titanium (Ti): 0.1% or less, niobium (Nb): 0.1% or less, vanadium (V): 0.2% or less, and molybdenum (Mo): 1% or less, a remainder of iron (Fe), and other unavoidable impurities,
wherein a microstructure comprises retained austenite having a volume fraction of 20% or more and annealed martensite having a volume fraction of 60% or more, and
the steel sheet contains 1013/m2 or more precipitates, each having a size of 30 nm or less.