Phosphatable part starting from a steel sheet coated with a metallic coating based on aluminum

Patent metadata

Field	Value
Publication number	US-12104255-B2
Application number	US-202217866628-A
Country	US
Kind code	B2
Filing date	Jul 18, 2022
Priority date	Jul 30, 2015
Publication date	Oct 1, 2024
Grant date	Oct 1, 2024

Abstract

A hardened part coated with a phosphatable coating is provided. The part is made by a method that includes providing a steel sheet pre-coated with a metallic coating including from 4.0 to 20.0% by weight of zinc, from 1.0 to 3.5% by weight of silicon, optionally from 1.0 to 4.0% by weight of magnesium, and optionally additional elements chosen from Pb, Ni, Zr, or Hf, the content by weight of each additional element being less than 0.3% by weight, the balance being aluminum and unavoidable impurities and residuals elements. The steel sheet is cut to obtain a blank, the blank is thermally treated at a temperature between 840 and 950° C. to obtain a fully austenitic microstructure in the steel, the blank is transferred into a press tool and hot-formed to obtain a part. The part is cooled to obtain a martensitic or martensitic-bainitic microstructure or made of at least 75% of equiaxed ferrite, from 5 to 20% of martensite and bainite in amount less than or equal to 10%.

First claim

What is claimed is:

1. A part comprising:
a part having a metallic coating obtained by a method including: A) providing a steel sheet pre-coated with a metallic coating including 4.0 to 20.0% by weight of zinc; 1.0 to 3.5% by weight of silicon; a balance being aluminum, unavoidable impurities and residual elements; and a ratio Zn/Si being between 3.2 and 8.0; B) cutting the coated steel sheet to obtain a blank; C) performing a thermal treatment on the blank at a temperature between 840 and 950° C. to obtain a fully austenitic microstructure in the steel; D) transferring the blank into a press tool; E) hot-forming the blank to obtain a part; F) cooling the part in order to obtain a microstructure in the steel being martensitic or martensitic-bainitic or made of at least 75% equiaxed ferrite, 5 to 20% of martensite and bainite in an amount less than or equal to 10%; and G) a phosphating step;
a ZnO layer on the metallic coating of the part, wherein the metallic coating does not comprise elements selected among In and Sn or combinations thereof; and
a phosphate crystals layer on the ZnO layer.

2. The part as recited in claim 1 wherein a coverage rate of phosphate crystals on the part surface is equal or greater than 90%.

3. The part as recited in claim 2 wherein the coverage rate of phosphate crystals on the part surface is equal or greater than 99%.

4. The part as recited in claim 1 further comprising an e-coating layer on the phosphate crystals layer.

5. The part as recited in claim 1 wherein the metallic coating comprises an intermetallic layer Fe3Al and an interdiffusion layer Fe—Si—Al.

6. The part as recited in claim 1 wherein a microstructure of the metallic coating comprises Zn2Mg phase or Mg2Si phase or both.

7. The part as recited in claim 1 wherein a microstructure of the metallic coating does not comprise metallic zinc.

8. The part as recited in claim 1 wherein the part is a press hardened steel part having a variable thickness.

9. The part as recited in claim 1 wherein the variable thickness is produced by a continuous flexible rolling process.

10. The part as recited in claim 1 wherein the part is a tailored rolled blank.

11. The part as recited in claim 1 wherein the part is a front rail, a seat cross member, a side sill member, a dash panel cross member, a front floor reinforcement, a rear floor cross member, a rear rail, a B-pillar, a door ring or a shotgun.

12. An automotive vehicle comprising:
the part as recited in claim 1 .

Assignees

• Arcelormittal

Inventors

• Machado Amorim Tiago
• Allely Christian
• Leuillier Gregory

Classifications

• C21D8/0257

  with diffusion of elements, e.g. decarburising, nitriding · CPC title

• C23C2/261

  in a gas atmosphere, e.g. inert or reducing atmosphere · CPC title

• C23C2/29

  Cooling or quenching · CPC title

• C23C2/26

  After-treatment (C23C2/14 takes precedence) · CPC title

• C21D1/673 Primary

  for die quenching · CPC title