	US 12,305,256 B2
	High-strength steel sheet and manufacturing method thereof
Young-Roc Im, Gwangyang-si (KR); Jae-Hoon Lee, Gwangyang-si (KR); Jong-Chan Park, Gwangyang-si (KR); Jong-Kweon Kim, Gwangyang-si (KR); Il-Hyun Kim, Gwangyang-si (KR); Tae-Kyo Han, Gwangyang-si (KR); and Tae-Oh Lee, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 17/624,511
Filed by POSCO, Pohang-si (KR)
PCT Filed Jul. 20, 2020, PCT No. PCT/KR2020/009557 § 371(c)(1), (2) Date Jan. 3, 2022, PCT Pub. No. WO2021/020789, PCT Pub. Date Feb. 4, 2021.
Claims priority of application No. 10-2019-0091891 (KR), filed on Jul. 29, 2019; and application No. 10-2019-0162642 (KR), filed on Dec. 9, 2019.
Prior Publication US 2022/0349019 A1, Nov. 3, 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 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/40 (2006.01)

CPC C21D 9/46 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (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 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C23C 2/0224 (2022.08); C23C 2/06 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/003 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)]

7 Claims

1. A high-strength steel sheet comprising:

by weight percent (wt %), 0.12% to less than 0.17% of carbon (C), 0.3% to 0.8% of silicon (Si), 2.5% to 3.0% of manganese (Mn), 0.4% to 1.1% of chromium (Cr), 0.01% to 0.3% of aluminum (Al), 0.01% to 0.03% of niobium (Nb), 0.01% to 0.03% of titanium (Ti), 0.001% to 0.003% of boron (B), 0.04% or less of phosphorus (P), 0.01% or less of sulfur (S): 0.01% or less of nitrogen (N), and a balance of iron (Fe) and inevitable impurities,

wherein the contents of C, Si, and Al satisfy mathematical equation (1) below,

a microstructure of the high-strength steel sheet includes, by area fraction, more than 1% to 4% or less of retained austenite, more than 10% to 20% or less of fresh martensite, 5% or less (excluding 0%) of ferrite, more than 50% to 70% or less of tempered martensite, and a balance of bainite,

wherein the number density of the retained austenite is 0.25/μm²or less,

an average effective diameter of the retained austenite is 0.2 to 0.4 μm, and

a proportion of the retained austenite having an effective diameter smaller than the average effective diameter is more than 60%,

[C]+([Si]+[Al])/5≤0.35 wt % [Equation (1)]

wherein [C], [Si] and [Al] refer to the wt % of C, Si and Al, respectively.