	US 12,270,087 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. 17/771,862
Filed by ArcelorMittal, Luxembourg (LU)
PCT Filed Oct. 20, 2020, PCT No. PCT/IB2020/059837 § 371(c)(1), (2) Date Apr. 26, 2022, PCT Pub. No. WO2021/084376, PCT Pub. Date May 6, 2021.
Claims priority of application No. PCT/IB2019/059285 (WO), filed on Oct. 30, 2019.
Prior Publication US 2022/0396845 A1, Dec. 15, 2022
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 7/13 (2006.01); C21D 8/02 (2006.01); C23C 2/12 (2006.01); C23C 2/26 (2006.01); C23C 2/28 (2006.01); C23C 14/35 (2006.01)

CPC C21D 7/13 (2013.01) [C21D 8/0205 (2013.01); C21D 8/0273 (2013.01); C23C 2/12 (2013.01); C23C 2/261 (2022.08); C23C 2/28 (2013.01); C23C 2/29 (2022.08); C23C 14/35 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C21D 2261/00 (2013.01)]

14 Claims

1. A press hardening method comprising the following steps:

A. providing a steel sheet for heat-treatment, precoated with a 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 to obtain a pre-alloyed steel sheet, wherein a heating rate of the batch annealing is above or equal to 5000° C.h⁻¹, cooling after the batch annealing being performed at a speed of 29.0° C.h⁻¹or less;

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, the microstructure being martensitic or being martensitic-bainitic or being 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 an amount less than or equal to 10% in volume.