US 12,442,055 B2
Method for producing a coated steel sheet having improved strength, ductility and formability
Jean-Philippe Masse, Grenoble (FR); and Jean-Christophe Hell, Maizieres-les-Metz (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Appl. No. 15/502,264
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Aug. 7, 2015, PCT No. PCT/IB2015/056029
§ 371(c)(1), (2) Date Feb. 7, 2017,
PCT Pub. No. WO2016/020899, PCT Pub. Date Feb. 11, 2016.
Claims priority of application No. PCT/IB2014/001492 (WO), filed on Aug. 7, 2014.
Prior Publication US 2017/0233847 A1, Aug. 17, 2017
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); C21D 1/18 (2006.01); C21D 1/19 (2006.01); C21D 1/26 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/34 (2006.01); C22C 38/38 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/12 (2006.01); C23C 2/40 (2006.01); C23F 17/00 (2006.01); C25D 3/22 (2006.01); C25D 3/56 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/012 (2013.01); B32B 15/013 (2013.01); C21D 1/185 (2013.01); C21D 1/19 (2013.01); C21D 1/26 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/34 (2013.01); C22C 38/38 (2013.01); C23C 2/02 (2013.01); C23C 2/022 (2022.08); C23C 2/0224 (2022.08); C23C 2/024 (2022.08); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/40 (2013.01); C23F 17/00 (2013.01); C25D 3/22 (2013.01); C25D 3/565 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 24 Claims
OG exemplary drawing
 
1. A coated steel sheet comprising:
a chemical composition of the steel including in weight %:
0.15%≤C≤0.25%;
1.2%≤Si≤1.8%;
2%≤Mn≤2.4%;
0.1%≤Cr≤0.25%; and
Al≤0.5%;
a balance being Fe and unavoidable impurities;
a microstructure including between 5% and 25% of intercritical ferrite, at least 50% of tempered martensite, at least 10% of residual austenite, less than 10% of fresh martensite and 0% or more of bainite, the fresh martensite being not auto-tempered, a sum of tempered martensite and bainite being of at least 60%;
wherein the coated steel sheet is coated with Zn or a Zn alloy, the coated steel sheet being hot-dip galvanized;
wherein the coated steel sheet has a yield strength of at least 550 MPa, a tensile strength of at least 980 MPa, a uniform elongation of at least 12%, a total elongation of at least 18%, and a hole expansion ratio of at least 30%, the hole expansion ratio being measured according to the standard ISO16630:2009.