US 12,168,810 B2
High-strength cold-rolled steel sheet having excellent bending workability and manufacturing method therefor
Hang-Sik Cho, Gwangyang-si (KR); and Young-Roc Im, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 17/413,259
Filed by POSCO, Pohang-si (KR)
PCT Filed Dec. 19, 2019, PCT No. PCT/KR2019/018106
§ 371(c)(1), (2) Date Jun. 11, 2021,
PCT Pub. No. WO2020/130675, PCT Pub. Date Jun. 25, 2020.
Claims priority of application No. 10-2018-0165144 (KR), filed on Dec. 19, 2018.
Prior Publication US 2022/0042133 A1, Feb. 10, 2022
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 38/22 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C23C 2/04 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 8/0236 (2013.01); C21D 8/0247 (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 38/22 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C23C 2/04 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 13 Claims
OG exemplary drawing
 
1. A cold-rolled steel sheet comprising:
by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chromium (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), and a balance of Fe and inevitable impurities;
by area fraction, 3-25% of ferrite, 20-40% of martensite, and 5-20% of retained austenite; and
a nickel concentration layer, formed by nickel (Ni) introduced from outside, as a surface layer,
wherein a concentration of nickel (Ni) at a depth of 1 μm from a surface is 0.15 wt % or more.