Method for the manufacture of a phosphatable part starting from a steel sheet coated with a metallic coating based on aluminum

Patent metadata

Field	Value
Publication number	US-11414737-B2
Application number	US-201615748262-A
Country	US
Kind code	B2
Filing date	Jul 29, 2016
Priority date	Jul 30, 2015
Publication date	Aug 16, 2022
Grant date	Aug 16, 2022

Abstract

A method for the manufacture of a hardened part coated with a phosphatable coating is provided. The method 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 method for the manufacture of a hardened part, such part being phosphated, comprising the following steps:
A) providing a steel sheet pre-coated with a metallic coating comprising:
4.0 to 20.0% by weight of zinc;
1.0 to 3.5% by weight of silicon;
the balance being aluminum, unavoidable impurities and residual elements; and
a ratio Zn/Si by weight being between 3.2 and 8.0;

B) cutting the steel sheet pre-coated with the metallic coating 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;
wherein the metallic coating does not comprise elements selected among In and Sn or combinations thereof.

2. The method according to claim 1 , wherein the metallic coating further comprises from 1.0 to 4.0% by weight of magnesium.

3. The method according to claim 1 , wherein the metallic coating further comprises additional elements chosen from Pb, Ni, Zr, or Hf, a content by weight of each additional element being less than 0.3%.

4. The method according to claim 1 , wherein the metallic coating comprises from 1.5 to 3.5% by weight of silicon.

5. The method according to claim 4 , wherein the metallic coating comprises from 1.5 to 2.5% by weight of silicon.

6. The method according to claim 4 , wherein the metallic coating comprises from 2.1 to 3.5% by weight of silicon.

7. The method according to claim 1 , wherein the metallic coating comprises from 10.0 to 15.0% by weight of zinc.

8. The method according to claim 1 , wherein the ratio of Zn/Si by weight is between 4 and 8.

9. The method according to claim 1 , wherein the ratio of Zn/Si by weight is between 4.5 and 7.5.

10. The method according to claim 1 , wherein the ratio of Zn/Si by weight is between 5 and 7.5.

11. The method according to claim 1 , wherein the metallic coating comprises from 1.1 to 3.0% by weight of magnesium.

12. The method according to claim 1 , wherein the metallic coating comprises greater than 76% by weight of aluminum.

13. The method according to claim 1 , wherein a thickness of the metallic coating is between 5 and 50 μm.

14. The method according to claim 13 , wherein the thickness of the metallic coating is between 10 and 35 μm.

15. The method according to claim 14 , wherein the thickness of the metallic coating is between 12 and 18 μm.

16. The method according to claim 14 , wherein the thickness of the metallic coating is between 26 and 31 μm.

17. The method according to claim 1 , wherein the metallic coating does not comprise elements selected among Cr, Mn, Ti, Ce, La, Nd, Pr, Ca, Bi, and Sb or combinations thereof.

18. The method according to claim 1 , wherein step C) is performed during a dwell time between 1 to 12 minutes in an inert atmosphere or an atmosphere comprising air.

19. The method according to claim 1 , wherein during step E) the hot-forming of the blank is performed at a temperature between 600 and 830° C.

20. The method according to claim 1 , wherein the phosphating step results in a ZnO layer on the metallic coating of the hardened part; and a phosphate crystals layer on the ZnO layer.

21. The method according to claim 1 , wherein a coverage rate of phosphate crystals on a part surface is equal or greater than 90%.

22. The method according to claim 21 , wherein the coverage rate of phosphate crystals on the part surface is equal or greater than 99%.

23. The part according to claim 20 , further comprising adding an e-coating layer on the phosphate crystals layer.

24. The method according to claim 1 , wherein the phosphating step results in a phosphate crystals outer layer.

Assignees

• Arcelormittal

Inventors

• Machado Amorim Tiago
• Allely Christian
• Leuillier Grégory

Classifications

• C22C21/10 Primary

  with zinc as the next major constituent · CPC title

• C21D1/673 Primary

  for die quenching · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C21/02

  with silicon as the next major constituent · CPC title