US 11,655,516 B2
Tempered and coated steel sheet having excellent formability and a method of manufacturing the same
Jean-Marc Pipard, Vaux (FR); and Marc Olivier Thenot, Malancourt-la-Montagne (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Appl. No. 16/467,643
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Dec. 15, 2017, PCT No. PCT/IB2017/057996
§ 371(c)(1), (2) Date Jun. 7, 2019,
PCT Pub. No. WO2018/116099, PCT Pub. Date Jun. 28, 2018.
Claims priority of application No. PCT/IB2016/057907 (WO), filed on Dec. 21, 2016.
Prior Publication US 2019/0338388 A1, Nov. 7, 2019
Int. Cl. C21D 9/46 (2006.01); C21D 1/20 (2006.01); C21D 1/22 (2006.01); C21D 8/02 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/22 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/38 (2006.01); C23C 2/06 (2006.01); C23C 2/40 (2006.01); B32B 15/01 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/012 (2013.01); C21D 1/20 (2013.01); C21D 1/22 (2013.01); C21D 8/0263 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/22 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/38 (2013.01); C23C 2/06 (2013.01); C23C 2/40 (2013.01); B32B 2605/08 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C22C 2204/00 (2013.01)] 19 Claims
 
1. A tempered and coated steel sheet having a composition comprising the following elements, expressed in percentage by weight:
0.17%≤carbon≤0.25%,
1.8%≤manganese≤2.3%,
0.5%≤silicon≤2.0%,
0.03≤aluminum≤1.2%,
sulphur≤0.03%,
phosphorus≤0.03%,
the remainder of the composition composed of iron and unavoidable impurities caused by processing,
the microstructure of said steel sheet comprising in area fraction, 4 to 20% residual austenite, 0 to 15% of ferrite, 40 to 85% tempered bainite and a minimum of 5% of tempered martensite, wherein the cumulated amounts of tempered martensite and residual austenite is between 10 and 30%, and
a yield strength above 700 MPa, an ultimate tensile strength above 950 MPa, a hole elongation ratio above 18%, a total elongation above 12%,
and wherein the tempered martensite is composed of laths elongated in one direction inside each grain issued from a primary austenite grain, in which iron carbide sticks which are 50 to 200 nm long are precipitated between the laths.