US 12,467,107 B2
Cold rolled steel sheet with ultra-high strength, and manufacturing method therefor
Hyun Seong Noh, Incheon (KR); Nam Hoon Goo, Incheon (KR); and Han Sol Maeng, Incheon (KR)
Assigned to Hyundai Steel Company, Incheon (KR)
Appl. No. 17/609,587
Filed by Hyundai Steel Company, Incheon (KR)
PCT Filed May 15, 2020, PCT No. PCT/KR2020/006387
§ 371(c)(1), (2) Date Nov. 8, 2021,
PCT Pub. No. WO2021/117989, PCT Pub. Date Jun. 17, 2021.
Claims priority of application No. 10-2019-0162495 (KR), filed on Dec. 9, 2019.
Prior Publication US 2022/0205059 A1, Jun. 30, 2022
Int. Cl. C21D 9/46 (2006.01); C21D 1/18 (2006.01); C21D 6/00 (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 38/12 (2006.01); C22C 38/14 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 1/18 (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); 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); C21D 2211/008 (2013.01)] 9 Claims
OG exemplary drawing
 
1. A cold-rolled steel sheet comprising: an amount of 0.10 to 0.40 wt % carbon (C), an amount of 0.10 to 0.80 wt % silicon (Si), an amount of 0.6 to 1.4 wt % manganese (Mn), an amount of 0.01 to 0.30 wt % aluminum (Al), an amount greater than 0 and less than or equal to 0.02 wt % phosphorus (P), an amount greater than 0 and less than or equal to 0.003 wt % sulfur (S), an amount greater than 0 and less than or equal to 0.006 wt % nitrogen (N), an amount greater than 0 and less than or equal to 0.05 wt % titanium (Ti), an amount of 0 to 0.05 wt % niobium (Nb), an amount of 0.001 to 0.003 wt % boron (B), and the remainder being iron (Fe) and other inevitable impurities, and
wherein the steel sheet has a microstructure comprising tempered martensite, and has a 90° bending workability (R/t; a ratio of the 90° bending radius (R) to the sheet thickness (t)) of 1.5 or less, and a mass ratio (Nb/Ti) of niobium (Nb) to titanium (Ti) of 1.5 or less;
wherein the microstructure has an average grain size of 6 μm or less,
wherein the microstructure contains at least one of titanium-based precipitates and niobium-based precipitates,
wherein the ratio of precipitates each having a size of 100 nm or less among the precipitates present in the unit area (1 μm2=1 μm×1 μm) at any point of the cold-rolled steel sheet to precipitates each having a size of more than 100 nm among the precipitates is 4:1 or greater, and
wherein a yield strength (YS) of 1,200 MPa or greater, a tensile strength (TS) of 1,470 MPa or greater, and an elongation (EL) of 5.0% or greater.