US 12,435,383 B2
High strength multi-phase steel having excellent burring properties at low temperature, and method for producing same
Sung-Il Kim, Gwangyang-si (KR); Seok-Jong Seo, Gwangyang-si (KR); and Hyun-Taek Na, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 16/467,226
Filed by POSCO, Pohang-si (KR)
PCT Filed Nov. 23, 2017, PCT No. PCT/KR2017/013408
§ 371(c)(1), (2) Date Jun. 6, 2019,
PCT Pub. No. WO2018/110853, PCT Pub. Date Jun. 21, 2018.
Claims priority of application No. 10-2016-0169718 (KR), filed on Dec. 13, 2016.
Prior Publication US 2020/0080167 A1, Mar. 12, 2020
Int. Cl. C21D 9/46 (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 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (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 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 2 Claims
OG exemplary drawing
 
1. A multi-phase steel comprising: by weight, carbon (C): 0.05% to 0.14%, silicon (Si): 0.01% to 1.0%, manganese (Mn): 1.0% to 3.0%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 1.0%, molybdenum (Mo): 0.003% to 0.3%, phosphorus (P): 0.001% to 0.05%, sulfur(S): 0.01% or less, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.06%, titanium (Ti): 0.005% to 0.13%, vanadium (V): 0.003% to 0.2%, boron (B): 0.0003% to 0.003%, a remainder of iron (Fe), and other inevitable impurities, wherein [C]* defined by the following Equations 1 and 2 is 0.022 or more and 0.10 or less, and the following Relationship 1 is satisfied,
[C]*=([C]+[N])−([C]+[N])×S  [Equation 1]
S=([Nb]/93+[Ti]/48+[V]/51+[Mo]/96)/([C]/12+[N]/14)  [Equation 2]
[Mn]+2.8[Mo]+1.5[Cr]+500[B]≤4.0  [Relationship 1]
where each of [C], [N], [Nb], [Ti], [V], [Mn], [Cr], [B], and [Mo] refers to a weight percentage (wt %) of respective elements;
a microstructure comprising: ferrite; bainite; and martensite-austenite (MA) constituents;
a yield strength of 560 MPa or more; and
a bake hardenability (BH) of 40 MPa or more,
wherein a sum of area ratios of the ferrite and the bainite is 97% to 99%, and an area ratio of the martensite-austenite (MA) constituents is 1% to 3%, wherein an area ratio of the ferrite is 20% or more, and an area ratio of the bainite is 17% or more, and
wherein, in the martensite-austenite (MA) constituents, a number of austenite structures having a diameter of 10 μm or more is 1×104/cm2 or less, including 0/cm2, and a number of austenite structures having a diameter of less than 10 μm is 1×108/cm2 or more.