Galvannealed steel sheet coated with an iron and nickel layer topped by a zinc-based layer

Patent metadata

Field	Value
Publication number	US-12091724-B2
Application number	US-202318094503-A
Country	US
Kind code	B2
Filing date	Jan 9, 2023
Priority date	Oct 24, 2017
Publication date	Sep 17, 2024
Grant date	Sep 17, 2024

Abstract

Galvannealed steel sheet having a steel substrate coated with a first alloy layer with iron and nickel directly topped by a second alloy layer based on zinc, the first and second alloyed layers being alloyed through diffusion such that the second alloy layer includes from 5 to 15 wt. % of iron, from 0 to 15 wt. % of nickel, a balance being zinc.

First claim

What is claimed is:

1. A galvannealed steel sheet obtainable from a method comprising the steps of providing a pre-coated steel sheet coated with a first coating consisting of iron and from 25% to 90%, by weight, nickel, such steel sheet having the following composition in weight percent:
0.10<C<0.40%,
1.5<Mn<3.0%,
0.7<Si<2.0%,
0.05<Al<1.0%
0.75<(Si+Al)<3.0%
and on a purely optional basis, one or more elements
Nb≤0.5%,
B≤0.005%,
Cr<1.0%,
Mo≤0.50%,
Ni≤1.0%,
Ti≤0.5%,
a remainder of the composition making up of iron and inevitable impurities resulting from processing; thermally treating the pre-coated steel sheet at a temperature between 600 to 1000° C.; hot-dip coating of the steel sheet obtained by the thermally treating step with a second coating based on zinc; and providing an alloying treatment to form the galvannealed steel sheet, the galvannealed steel sheet comprising:
a steel substrate coated with a first alloy layer consisting of iron and nickel directly topped by a second alloy layer based on zinc, the first and second alloyed layers being alloyed through diffusion such that the second alloy layer includes from 5 to 15 wt. % of iron, from 1 to 15 wt. % of nickel, a balance being zinc.

2. The galvannealed steel sheet as recited in claim 1 wherein a microstructure of the steel substrate includes from 1 to 50% of residual austenite, from 1 to 60% of martensite and optionally at least one element chosen from: bainite, ferrite, cementite and pearlite.

3. The galvannealed steel sheet as recited in claim 2 wherein the microstructure includes from 5 to 25% of residual austenite.

4. The galvannealed steel sheet as recited in claim 2 wherein the microstructure includes from 1 to 60% of tempered martensite.

5. The galvannealed steel sheet as recited in claim 2 wherein the microstructure includes from 10 to 40% of bainite.

6. The galvannealed steel sheet as recited in claim 2 wherein the microstructure includes from 1 to 25% of ferrite.

7. The galvannealed steel sheet as recited in claim 2 wherein the microstructure includes from 1 to 15% of untempered martensite.

8. The galvannealed steel sheet as recited in claim 1 wherein the galvannealed steel sheet is obtained from the method and has a tensile strength above or equal to 500 MPa.

9. The galvannealed steel sheet as recited in claim 1 wherein the steel substrate has the composition of the steel sheet.

10. The galvannealed steel sheet as recited in claim 1 wherein an amount of Fe in the first coating is between 25 to 65%, by weight.

11. The galvannealed steel sheet as recited in claim 10 wherein the amount of Fe in the first coating is between 40 to 60%, by weight.

12. The galvannealed steel sheet as recited in claim 11 wherein the amount of Ni in the first coating is from 35 to 75%, by weight.

13. The galvannealed steel sheet as recited in claim 12 wherein the amount of Ni in the first coating is from 40 to 60%, by weight.

14. The galvannealed steel sheet as recited in claim 12 wherein the first coating has a thickness between 0.8 and 5.0 μm.

15. A spot welded joint comprising:
at least two metal sheets including a first metal sheet being the galvannealed steel sheet as recited in claim 1 , the joint containing less than 3 cracks having a size above 100 μm and wherein the longest crack has a length below 400 μm.

16. The spot welded joint as recited in claim 15 wherein a second metal sheet of the metal sheets is a steel sheet or an aluminum sheet.

17. The spot welded joint as recited in claim 15 wherein a second metal sheet of the metal sheets is a galvannealed steel sheet including a second steel substrate coated with a further first alloy layer comprising iron and nickel directly topped by a further second alloy layer based on zinc, the further first and further second alloy layers being alloyed through diffusion such that the further second alloy layer includes from 5 to 15 wt. % of iron, from 0 to 15 wt. % of nickel, a balance being zinc.

18. The spot welded joint as recited in claim 15 wherein the at least two metals sheets include a third metal sheet being a steel sheet or an aluminum sheet.

19. An automotive vehicle part comprising the steel sheet as recited in claim 1 .

Assignees

• Arcelormittal

Inventors

• Chakraborty Anirban
• Ghassemi-Armaki Hassan

Classifications

• C23C2/02

  Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) · CPC title

• C23C2/0224

  Two or more thermal pretreatments · CPC title

• C23C2/022

  by heating · CPC title

• C23C28/027

  including at least one metal matrix material comprising a mixture of at least two metals or metal phases or metal matrix composites, e.g. metal matrix with embedded inorganic hard particles, CERMET, MMC. · CPC title

• C23C28/025

  with at least one zinc-based layer · CPC title