	US 12,480,173 B2
	Cold rolled annealed steel sheet with high hole expansion ratio and manufacturing process thereof
Jean-Christophe Hell, Metz (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Appl. No. 17/294,173
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Nov. 30, 2018, PCT No. PCT/IB2018/059510 § 371(c)(1), (2) Date May 14, 2021, PCT Pub. No. WO2020/109850, PCT Pub. Date Jun. 4, 2020.
Prior Publication US 2022/0010398 A1, Jan. 13, 2022
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 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01)

CPC C21D 9/46 (2013.01) [C21D 6/001 (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); 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 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)]

21 Claims

1. A cold rolled annealed steel sheet having a chemical composition comprising, in weight %:

0.30%≤C≤0.50%

1.00%≤Mn≤2.50%

1.00%≤Si≤2.00%

Al≤2.00%,

Cr≤0.100%,

0.100%≤Mo≤0.500%,

0.020%≤Nb≤0.200%

B≤0.0005%,

P≤0.02%,

S≤0.005%,

N≤0.01%,

a remainder being Fe and unavoidable impurities, with the percentages in carbon, manganese, chromium, molybdenum and boron are such that the alloy satisfies the following condition:

250% C+120% Mn−200% Cr+200% Mo−10000% B≥320, and

a microstructure consisting of in surface fraction, 35% to 45% of islands of martensite and retained austenite (M-A), a total of the retained austenite being higher than or equal to 24%, and a remainder consisting of bainitic ferrite.