Cold rolled and annealed steel sheet, method of production thereof and use of such steel to produce vehicle parts

Patent metadata

Field	Value
Publication number	US-11486017-B2
Application number	US-201716302977-A
Country	US
Kind code	B2
Filing date	May 23, 2017
Priority date	May 24, 2016
Publication date	Nov 1, 2022
Grant date	Nov 1, 2022

Abstract

A cold rolled and annealed steel sheet includes by weight: 0.6<C<1.3%,15.0<Mn<35%, 6.0<Al<15%, Si<2.40%, S<0.015%, P<0.1%, N<0.1%, iron and inevitable impurities, optionally one or more of Ni, Cr and Cu in an individual amount of up to 3% and optionally one or more of B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0%, a microstructure of the sheet comprising at least 0.1% of intragranular kappa carbides, at least 80% of the kappa carbides have an average size below 30 nm, the remainder being made of austenite, an average grain size of the austenite being below 6 μm, an average aspect ratio of the austenite being between 1.5 and 6, an average grain size of the ferrite, when present being below 5 μm, and an average aspect ratio of the ferrite, when present, being below 3.0.

First claim

What is claimed is:

1. A cold rolled and twice annealed steel sheet comprising by weight:
6<C<1.3%,
15.0≤Mn <35%,
6.0≤Al <15%,
Si ≤2.40%,
S≤0.015%,
P≤0.1%,
N ≤0.1%,
the remainder of the composition made up of iron and inevitable impurities resulting from elaboration,
a microstructure of said cold rolled and twice annealed steel sheet consists of at least 0.1% in volume fraction of intragranular kappa carbides, wherein at least 80% of said kappa carbides have an average size below 30 nm, 0 to 10% in area fraction of granular ferrite, and austenite, an average grain size of the austenite being below 6 μm, an average aspect ratio of the austenite being between 1.5 and 6, an average grain size of the granular ferrite, when present being below 5 μm, and an average aspect ratio of the granular ferrite, when present, being below 3.0.

2. The cold rolled and twice annealed steel sheet according to claim 1 , further comprising one or more elements chosen among Ni, Cr and Cu in an individual amount of up to 3% by weight and optionally one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0% by weight.

3. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the carbon content is between 0.8 and 1.0% by weight.

4. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the manganese content is between 18 and 30% by weight.

5. The cold rolled and twice annealed steel sheet according to claim 3 , wherein the manganese content is between 18 and 30% by weight.

6. The cold rolled and twice annealed steel sheet according to claim 3 , wherein the aluminum content is between 8.5 and 10% by weight.

7. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the steel sheet is covered by a metallic coating.

8. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the steel sheet is covered by an aluminum-based coating or a zinc-based coating.

9. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the average grain size of the austenite is below 3 μm.

10. The cold rolled and twice annealed steel sheet according to claim 4 , wherein the aluminum content is between 7 and 12% by weight.

11. The cold rolled and twice annealed steel sheet according to claim 10 , wherein Si<2.0%,by weight.

12. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the density is <7.1 g/cm 3 .

13. The cold rolled and twice annealed steel sheet according to claim 1 , wherein the density is <7 g/cm 3 .

14. The cold rolled and twice annealed steel sheet according to claim 1 , wherein 0.8<C<1.0%, 18<Mn<30%, 8<Al<10%, the average grain size of the austenite is below 3 μm, wherein the steel sheet has an ultimate tensile strength of at least 1000 MPa, a yield strength of at least 900 MPa and a density below 7 g/cm 3 .

15. A structural or safety part of a vehicle comprising a steel sheet according to claim 1 .

16. A structural or safety part of a vehicle obtained by flexible rolling of a steel sheet according to claim 1 .

17. A vehicle comprising the structural or safety part of claim 15 .

18. A vehicle comprising the structural or safety part of claim 16 .

19. A method for producing a steel sheet comprising:
feeding a slab which has a composition, by weight of: 0.6<C<1.3%, 15.0<Mn<35% 6.0<Al<15%, Si<2.40%, S<0.015%, P<0.1%, N<0.1%, the remainder of the composition made up of iron and inevitable impurities resulting from elaboration;
reheating the slab at a temperature above 1000° C. and hot rolling the slab with a final rolling temperature of at least 800° C. to obtain a hot rolled steel sheet,
coiling the hot rolled steel sheet at a temperature below 600° C.,
cold-rolling the hot rolled steel sheet at a reduction comprised between 30 and 80% to obtain a cold rolled sheet,
first annealing of the cold rolled sheet by heating the cold rolled sheet up to a first annealing temperature between 700 and 1000° C., holding the cold rolled sheet at the first annealing temperature for less than 5 minutes and then cooling the cold rolled sheet at a rate of at least 30° C./s to obtain an annealed sheet,
second annealing the annealed sheet by heating the annealed sheet up to a second annealing temperature between 400 and 700° C., holding the annealed sheet at the second annealing temperature for 1 minute to 150 hours and then cooling the annealed sheet at a rate of at least 30° C./s to obtain the cold rolled and twice annealed steel sheet according to claim 1 .

20. A method according to claim 19 , wherein the composition further includes one or more elements chosen among Ni, Cr and Cu in an individual amount of up to 3% by weight and optionally one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0% by weight.

21. A method according to claim 19 , wherein the first annealing temperature is between 800 and 950° C.

22. A method according to claim 19 , wherein the coiling temperature is between 350 and 500° C.

23. A method according to claim 21 , wherein the holding time of the second annealing is between 2 and 10 hours.

24. A method according to claim 22 , wherein the holding time of the second annealing is between 2 and 10 hours.

25. A method according to claim 19 , further comprising a final coating step.

Assignees

• Arcelormittal

Inventors

• Soler Michel
• Zuazo Rodriguez Ian Alberto
• De Diego Calderon Irène

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C23C2/12

  Aluminium or alloys based thereon · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title

• Y02P10/20

  Recycling · CPC title

• C21D8/0436

  Cold rolling · CPC title