US 12,448,664 B2
Press hardening method
Raisa Grigorieva, Metz (FR); Florin Duminica, Tilff (BE); Brahim Nabi, Leuven (BE); Pascal Drillet, Rozérieulles (FR); and Thierry Sturel, Le Ban Saint Martin (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Appl. No. 17/771,908
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Oct. 20, 2020, PCT No. PCT/IB2020/059842
§ 371(c)(1), (2) Date Apr. 26, 2022,
PCT Pub. No. WO2021/084379, PCT Pub. Date May 6, 2021.
Claims priority of application No. PCT/IB2019/059288 (WO), filed on Oct. 30, 2019.
Prior Publication US 2022/0380863 A1, Dec. 1, 2022
Int. Cl. C21D 9/46 (2006.01); B21D 22/02 (2006.01); B32B 15/01 (2006.01); C21D 1/74 (2006.01); C21D 7/13 (2006.01); C21D 8/02 (2006.01); C23C 2/26 (2006.01); C23C 2/28 (2006.01); C22C 18/04 (2006.01); C22C 21/10 (2006.01)
CPC C21D 9/46 (2013.01) [B21D 22/022 (2013.01); B32B 15/012 (2013.01); B32B 15/015 (2013.01); C21D 1/74 (2013.01); C21D 7/13 (2013.01); C21D 8/0205 (2013.01); C23C 2/26 (2013.01); C23C 2/261 (2022.08); C23C 2/28 (2013.01); C23C 2/29 (2022.08); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C22C 18/04 (2013.01); C22C 21/10 (2013.01)] 19 Claims
 
1. A press hardening method comprising the following steps:
A. providing a steel sheet for heat treatment, the steel sheet being optionally coated with a zinc-based pre-coating or an aluminum-based pre-coating;
B. flexible rolling the steel sheet in a rolling direction so as to obtain a steel sheet having a variable thickness;
C. cutting the rolled steel sheet to obtain a tailored rolled blank;
D. depositing a hydrogen barrier pre-coating with a thickness from 10 to 550 nm, the hydrogen barrier pre-coating consisting of nickel and chromium;
E. heat treating the tailored rolled blank to obtain a fully austenitic microstructure in the steel sheet;
F. transferring the tailored rolled blank into a press tool;
G. hot-forming the tailored rolled blank to obtain a part having a variable thickness;
H. cooling of the part obtained in step G to obtain a microstructure in steel being (i) martensitic or (martensito-bainitic or (made of at least 75% in terms of volume fraction of equiaxed ferrite, from 5 to 20% in volume of martensite and of bainite in amount less than or equal to 10% in volume.