US 12,454,731 B2
Hot-dip galvannealed steel sheet with ultra-high strength and high formability, and manufacturing method therefor
Ho Yong Um, Incheon (KR); Nam Hoon Goo, Incheon (KR); Min Sung Kim, Incheon (KR); and Gyu Jin Oh, Incheon (KR)
Assigned to Hyundai Steel Company, Incheon (KR)
Appl. No. 17/608,409
Filed by Hyundai Steel Company, Incheon (KR)
PCT Filed May 15, 2020, PCT No. PCT/KR2020/006386
§ 371(c)(1), (2) Date Nov. 2, 2021,
PCT Pub. No. WO2021/117988, PCT Pub. Date Jun. 17, 2021.
Claims priority of application No. 10-2019-0162494 (KR), filed on Dec. 9, 2019.
Prior Publication US 2022/0307100 A1, Sep. 29, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. 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); C23C 2/02 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 8/0205 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (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); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01)] 15 Claims
OG exemplary drawing
 
1. A hot-dip galvannealed steel sheet, comprising:
a base steel sheet; and
a hot-dip galvannealed layer formed on the surface of the base steel sheet;
wherein the base steel sheet comprises: an amount of 0.05 to 0.15 wt % of carbon (C), an amount greater than 0 and less than or equal to 1.0 wt % of silicon (Si), an amount of 4.0 to 9.0 wt % of manganese (Mn), an amount greater than 0 and less than or equal to 0.6 wt % of aluminum (Al), an amount greater than 0 and less than or equal to 0.02 wt % of phosphorus (P), an amount of greater than 0 and less than or equal to 0.005 wt % of sulfur(S), an amount of greater than 0 and less than or equal to 0.006 wt % of nitrogen (N), and the balance being iron (Fe) and other inevitable impurities;
the base steel sheet has a microstructure composed of ferrite and retained austenite,
the average grain size of the microstructure is 3 μm or less,
a fraction of high-angle grain boundaries among the grains in the base steel sheet is 60% or greater,
wherein the high-angle grain boundary is a grain boundary in which an angle between adjacent grains is 15° or greater, and
the hot-dip galvannealed steel sheet has a yield strength (YS) of 800-1100 MPa, a tensile strength (TS) of 980-1200 MPa, an elongation (EL) of 25-30%, and a hole expansion ratio (HER) of 20-30%.