US 11,920,208 B2
High strength and high formability steel sheet and manufacturing method
Coralie Jung, Racrange (FR); Astrid Perlade, Le Ban-Saint-Martin (FR); Kangying Zhu, Metz (FR); and Frédéric Kegel, Yutz (FR)
Assigned to ARCELORMITTAL, Luxembourg (LU)
Appl. No. 16/954,510
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Dec. 18, 2018, PCT No. PCT/IB2018/060247
§ 371(c)(1), (2) Date Jun. 16, 2020,
PCT Pub. No. WO2019/123245, PCT Pub. Date Jun. 27, 2019.
Claims priority of application No. PCT/IB2017/058122 (WO), filed on Dec. 19, 2017.
Prior Publication US 2021/0087646 A1, Mar. 25, 2021
Int. Cl. C21D 9/46 (2006.01); B23K 11/16 (2006.01); B32B 15/01 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (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); C22C 38/38 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/12 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01); B23K 101/00 (2006.01)
CPC C21D 9/46 (2013.01) [B23K 11/16 (2013.01); B32B 15/012 (2013.01); B32B 15/013 (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); 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 38/06 (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); C22C 38/38 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/29 (2022.08); C23C 2/40 (2013.01); B23K 2101/006 (2018.08); C21D 2211/001 (2013.01); C21D 2211/003 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 19 Claims
 
1. A method for manufacturing a cold-rolled and heat-treated steel sheet, comprising the following successive steps:
casting a steel so as to obtain a slab, the steel having a composition comprising, by weight percent:
0.10%≤C≤0.25%,
3.5%≤Mn≤6.0%,
0.5%≤Si≤2.0%,
0.3%≤Al≤1.2%,
with Si+Al≥0.8%,
0.10%≤Mo≤0.50%,
S≤0.010%,
P≤0.020%,
N≤0.008%,
and optionally one or more elements selected from a group consisting of Cr, Ti, Nb, V and B, such that by weight percent:
0.01%≤Cr≤1.0%,
0.010%≤Ti≤0.080%,
0.010%≤Nb≤0.080%,
0.010%≤V≤0.30%,
0.0005%≤B≤0.004%,
a remainder of the composition being iron and unavoidable impurities resulting from the smelting;
reheating the slab at a temperature Treheat comprised between 1150° C. and 1300° C.;
hot rolling the reheated slab at a temperature higher than Ar3 to obtain a hot rolled steel sheet;
coiling the hot rolled steel sheet at a coiling temperature Tcoil comprised between 20° C. and 600° C.;
annealing the hot rolled steel sheet at a first annealing temperature TA1 comprised between 500° C. and TA1max, TA1max being the temperature at which at most 30% of austenite is created upon heating, the hot-rolled steel sheet being maintained at the first annealing temperature TA1 for a time tai comprised between 3 s and 50000 s, to obtain a hot-rolled and annealed steel sheet;
cold rolling the hot-rolled and annealed steel sheet so as to obtain a cold rolled steel sheet;
reheating the cold-rolled steel sheet to a second annealing temperature TA2 comprised between 770° C. and Ae3 and maintaining the cold-rolled steel sheet at the second annealing temperature TA2 for a holding time to comprised between 30 s and 500 s, so as to obtain, upon annealing, a structure comprising between 55 and 90% of austenite and between 10% and 45% of ferrite;
quenching the cold-rolled steel sheet at a cooling rate Vc comprised between 1° C./s and 100° C./s, to a quenching temperature QT comprised between 20° C. and Ms−50° C.;
reheating the cold-rolled steel sheet to a partitioning temperature TP comprised between 350° C. and 500° C., and maintaining the cold-rolled steel sheet at a partitioning temperature TP for a partitioning time tp comprised between 3 s and 1000 s; and
cooling the cold-rolled steel sheet to a room temperature, to obtain a cold-rolled and heat treated steel sheet, wherein the cold-rolled and heat-treated steel sheet has a total elongation TE, measured according to ISO standard ISO 6892-1, of at least 14% and a hole expansion ratio HER, measured according to the ISO standard 16630:2009, of at least 20%.