	US 12,281,366 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. 17/771,874
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Oct. 20, 2020, PCT No. PCT/IB2020/059838 § 371(c)(1), (2) Date Apr. 26, 2022, PCT Pub. No. WO2021/084377, PCT Pub. Date May 6, 2021.
Claims priority of application No. PCT/IB2019/059286 (WO), filed on Oct. 30, 2019.
Prior Publication US 2022/0380861 A1, Dec. 1, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 1/18 (2006.01); C21D 1/26 (2006.01); C21D 1/76 (2006.01); C21D 8/02 (2006.01); C21D 9/48 (2006.01); C23C 2/06 (2006.01); C23C 2/12 (2006.01); C23C 2/26 (2006.01); C23C 2/28 (2006.01)

CPC C21D 1/18 (2013.01) [C21D 1/26 (2013.01); C21D 1/76 (2013.01); C21D 8/0247 (2013.01); C21D 9/48 (2013.01); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/26 (2013.01); C23C 2/261 (2022.08); C23C 2/28 (2013.01); C23C 2/29 (2022.08)]

13 Claims

1. A press hardening method comprising the following steps:

A. providing a steel sheet for heat treatment, precoated with an anti-corrosion zinc—or aluminum-based pre-coating;

B. depositing a hydrogen barrier pre-coating with a thickness from 10 to 550 nm;

C. batch annealing the precoated steel sheet in an inert atmosphere to obtain a pre-alloyed steel sheet, the heating rate of the batch annealing is above or equal to 5000° ch−1;

D. cutting the pre-alloyed steel sheet to obtain a blank;

E. thermally treating the blank to obtain a fully austenitic microstructure in the steel sheet;

F. transferring the blank into a press tool;

G. hot-forming the blank to obtain a part;

H. cooling the part obtained in step G) in order to obtain a microstructure in the steel sheet being martensitic or martensitic-bainitic or made of at least 75% in terms of volume fraction of equiaxed ferrite, from 5 to 20% in volume of martensite and bainite in an amount less than or equal to 10% in volume.