Method of production of a cold rolled and heat treated steel sheet to produce vehicle parts

Patent metadata

Field	Value
Publication number	US-12247274-B2
Application number	US-202017060493-A
Country	US
Kind code	B2
Filing date	Oct 1, 2020
Priority date	Dec 22, 2016
Publication date	Mar 11, 2025
Grant date	Mar 11, 2025

Abstract

A method of production of a cold rolled and heat treated steel sheet has the following steps: providing a cold rolled steel sheet with a composition including the following elements, expressed in percent by weight: 0.15%≤carbon≤0.6%, 4%≤manganese≤20%, 5%≤aluminum≤15%, 0≤silicon≤2%, aluminum+ silicon≥6.5%, a remainder being composed of iron and unavoidable impurities caused by processing; heating said cold rolled steel sheet up to a soaking temperature between 80° and 950° C. during less than 600 seconds, then cooling the sheet down to a temperature in a range of 600° C. to room temperature, reheating the steel sheet to a soaking temperature of 150° C. to 600° C. during 10 s to 250 h, then cooling the sheet.

First claim

What is claimed is:

1. A method of production of a cold rolled and heat treated steel sheet comprising the following steps:
providing a cold rolled steel sheet with a composition consisting of the following elements, expressed in percent by weight:
0.15%≤carbon≤0.6%,
4%≤manganese≤20%,
5%≤aluminum≤15%,
0≤silicon≤2%,
aluminum+ silicon≥6.5%,
optionally one or more elements selected from the group consisting of niobium, titanium, vanadium, copper, nickel, cerium, boron, magnesium, zirconium, molybdenum, tantalum, tungsten, sulfur, and phosphorus,
a remainder being composed of iron and unavoidable impurities caused by processing;

heating said cold rolled steel sheet up to a soaking temperature between 80° and 950° C. for a duration of less than 600 seconds, then cooling the sheet down to room temperature,
reheating the steel sheet at a heating rate of at least 10° C./h to a soaking temperature of 150° C. to 600° C. for a duration of 10 s to 250 h, then cooling the sheet to room temperature,
wherein after the reheating the steel sheet has an ultimate tensile strength higher than 900 MPa, and a microstructure of the steel sheet consisting of, in area fraction, 10 to 50% of austenite, at least 0.1% of ordered ferrite of D0 3 structure, a remainder of the microstructure being regular ferrite and optionally up to 2% of intragranular kappa carbides.

2. The method as recited in claim 1 wherein after the reheating a microstructure of the steel sheet consists in area fraction, 10 to 50% of austenite, a remainder of the microstructure being regular ferrite and ordered ferrite of D0 3 structure.

3. The method as recited in claim 1 wherein aluminum, manganese and carbon amounts are such that 0.3<(Mn/2Al) x exp (C)<2.

4. The method as recited in claim 1 wherein the manganese content is between 7 and 15%.

5. The method as recited in claim 1 the aluminum content of the composition is equal or higher than 7%, and wherein a microstructure after the reheating includes in area fraction a kappa carbides concentration higher than 1%.

6. The method as recited in claim 1 wherein after the reheating the steel sheet has a density of less than or equal to 7.4 g/cm 3 and a uniform elongation higher than or equal to 9%.

7. A method for the manufacture of structural or safety parts of a vehicle comprising the method as recited in claim 1 .

8. The method as recited in claim 1 wherein the composition consists of the following elements, expressed in percent by weight:
0.15%≤carbon≤0.6%,
4%≤manganese≤20%,
5%≤aluminum≤15%,
0≤silicon≤2%,
aluminum+ silicon≥6.5%, and

one or more of the following elements:
0.01%≤niobium≤0.3%,
0.01%≤titanium≤0.2%,
0.01%≤vanadium≤0.6%,
0.01%≤copper≤2.0%,
0.01%≤nickel≤2.0%,
cerium≤0.1%,
boron≤0.01%,
magnesium≤0.05%,
zirconium≤0.05%,
molybdenum≤2.0%,
tantalum≤2.0%,
tungsten≤2.0%,
sulfur,
phosphorous,
a remainder being composed of iron and unavoidable impurities caused by processing.

9. The method as recited in claim 2 wherein the austenite phase includes intragranular kappa carbides.

10. The method as recited in claim 2 wherein the microstructure includes up to 2% of intragranular kappa carbides inside ferrite grains.

11. The method as recited in claim 1 , wherein after reheating the steel sheet has an ultimate tensile strength higher than or equal to 1000 MPa.

12. The method as recited in claim 2 , wherein after reheating the steel sheet has an ultimate tensile strength higher than or equal to 1000 MPa.

13. The method of claim 2 , further comprising, after said reheating and cooling, further reheating the steel sheet to a temperature of 460-500° C., and then hot dip coating with zinc.

14. The method of claim 1 , wherein the microstructure includes at least 1.0% ordered ferrite of D0 3 structure.

15. The method of claim 1 , wherein the microstructure includes more than 3% ordered ferrite of D0 3 structure.

16. The method of claim 2 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 30 nm.

17. The method of claim 2 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 10 nm.

18. The method of claim 2 , wherein the microstructure consists of austenite, ferrite and ordered ferrite of D0 3 structure.

19. The method of claim 2 , wherein the microstructure consists of austenite, ferrite, ordered ferrite of D0 3 structure and intragranular kappa carbides.

20. The method of claim 14 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 30 nm.

21. The method of claim 20 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 10 nm.

22. The method of claim 15 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 30 nm.

23. The method of claim 22 , wherein at least 80% of the ordered ferrite of D0 3 structure has an average size below 10 nm.

24. The method of claim 1 , wherein the providing the cold rolled sheet includes
providing a semi-finished product with said composition;
hot rolling the semi-finished product to obtain a hot rolled sheet, wherein the hot rolling finishing temperature is greater than 800° C.,
cooling the hot rolled sheet at a cooling rate less than or equal to 100° C./s down to a coiling temperature below 600° C.,
coiling the hot rolled sheet at the coiling temperature,
cold rolling the hot rolled sheet with a thickness reduction between 35 to 90% to provide the cold rolled sheet.

25. The method of claim 24 , wherein after said coiling and before said cold rolling, the method includes hot band annealing the hot rolled sheet between 400° C. and 1000° C.

26. The method as recited in claim 9 wherein the microstructure includes up to 2% of intragranular kappa carbides inside ferrite grains.

27. A method of production of a cold rolled and heat treated steel sheet comprising the following steps:
providing a cold rolled steel sheet with a composition including the following elements, expressed in percent by weight:
0.15%≤carbon≤0.6%,
4%≤manganese≤20%,
5%≤aluminum≤15%,
0≤silicon≤2%,
aluminum+ silicon≥6.5%,
0.01%≤copper≤2.0%,
a remainder being composed of iron and unavoidable impurities caused by processing;

heating said cold rolled steel sheet up to a soaking temperature between 80° and 950° C. for a duration of less than 600 seconds, then cooling the sheet down to room temperature,
reheating the steel sheet at a heating rate of at least 10° C./h to a soaking temperature of 150° C. to 600° C. for a duration of 10 s to 250 h, then cooling the sheet to room temperature, wherein after the reheating the steel sheet has an ultimate tensile strength higher than 900 MPa, and a microstructure of the steel sheet consisting of, in area fraction, 10 to 50% of austenite, a remainder of the microstructure being regular ferrite and ordered ferrite of D0 3 structure and optionally up to 2% of intragranular kappa carbides.

28. The method of claim 27 , wherein the microstructure includes in area fraction at least 0.1% ordered ferrite of D0 3 structure.

29. A method of production of a cold rolled and heat treated steel sheet comprising the following steps:
providing a cold rolled steel sheet with a composition including the following elements, expressed in percent by weight:
0.15%

Assignees

• Arcelormittal

Inventors

• Barges Patrick
• Zuazo Rodriguez Ian Alberto

Classifications

• C22C38/16

  containing copper · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C22C38/08

  containing nickel {(C22C38/105 takes precedence)} · CPC title

• C22C38/06

  containing aluminium · CPC title