US 12,084,738 B2
Method for producing a steel sheet having improved strength, ductility and formability
Hyun Jo Jun, East Chicago, IN (US); and Pavan Venkatasurya, East Chicago, IN (US)
Assigned to ARCELORMITTAL, Luxembourg (LU)
Appl. No. 16/064,513
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Dec. 21, 2016, PCT No. PCT/EP2016/082192
§ 371(c)(1), (2) Date Jun. 21, 2018,
PCT Pub. No. WO2017/108956, PCT Pub. Date Jun. 29, 2017.
Claims priority of application No. PCT/IB2015/059837 (WO), filed on Dec. 21, 2015.
Prior Publication US 2019/0003005 A1, Jan. 3, 2019
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); B32B 15/18 (2006.01); C21D 1/22 (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 38/26 (2006.01); C23C 2/00 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); B32B 15/18 (2013.01); C21D 1/22 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/02 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C22C 38/001 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/26 (2013.01); C23C 2/00 (2013.01); C23C 2/0224 (2022.08); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/29 (2022.08); 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)] 21 Claims
 
1. A steel sheet, comprising:
a chemical composition comprising, by weight:
18% ≤C≤0.25%,
0.9% ≤Si≤1.8%,
0.02% ≤Al≤1.0%,
with 1.0% ≤Si+Al≤2.35%,
1.5% ≤Mn≤2.5%,
0.010% ≤Nb≤0.035%,
0.10% ≤Cr≤0.40%, and
a remainder, the remainder including Fe and unavoidable impurities; and
a microstructure consisting of, in area fraction:
20% to 50% intercritical ferrite,
10% to 20% retained austenite,
25% to 45% tempered martensite,
bainite,
a sum of the tempered martensite and the bainite area fractions being between 30% and 60%, and
10% to 20% fresh martensite,
wherein the steel sheet has a yield strength between 440 and 750 MPa, a tensile strength of at least 980 MPa, a total elongation of at least 20%, and a hole expansion ratio HER according to ISO standard 16630:2009 of at least 20%.