High formability steel sheet for the manufacture of lightweight structural parts and manufacturing process

• US 11,427,898 B2
• Filed: 04/20/2018
• Issued: 08/30/2022
• Est. Priority Date: 04/21/2017
• Status: Active Grant

• Current Assignee: Arcelormittal (ArcelorMittal SA)
• Original Assignee: Arcelormittal (ArcelorMittal SA)
• Inventors: Bonnet, Frederic, Bobadilla, Manuel, Bele, Bertrand, Daeschler, Valerie
• Primary Examiner(s): Dumbris, Seth
• Application Number:
  US16/605,690
• Publication Number:
  US 20200131607A1
• Time in Patent Office: 1,593 Days
• Field of Search: 420126, 420120, 420103, 148507, 148540
• CPC Class Codes: B22D 11/001 of specific alloys
• CPC Class Codes: B22D 11/0622 formed by two casting wheels
• CPC Class Codes: B22D 11/1206 for plastic shaping of strands rolling mills B21B1/46
• CPC Class Codes: B22D 11/225 for secondary cooling
• CPC Class Codes: C21D 2211/001 Austenite
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 8/0215 Rapid solidification; Thin strip casting
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0236 Cold rolling
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/32 with boron

Abstract

A steel sheet has a composition comprising, by weight: 0.010%≤C≤0.080%, 0.06%≤Mn≤3%, Si≤1.5%, 0.005%≤Al≤1.5%, S≤0.030%, P≤0.040%, Ti and B such that: 3.2%≤Ti≤7.5% and (0.45×Ti)−1.35≤B≤(0.45×Ti)−0.43, optionally Ni≤1%, Mo≤1%, Cr≤3%, Nb≤0.1%, V≤0.1%, the remainder being iron and unavoidable impurities resulting from the smelting. The steel sheet has a structure consisting of ferrite, at most 10% of austenite, and precipitates comprising eutectic precipitates of TiB₂, the volume fraction of TiB₂ precipitates with respect to the whole structure being of at least 9%, the proportion of TiB₂ precipitates having a surface area lower than 8 μm² being of at least 96%.

Claims

1. A steel sheet made of a steel having a composition comprising, by weight percent:

0.010%≤

C≤

0.080%

0.06%≤

Mn≤

3%

Si≤

1.5%

0.005%≤

Al≤

1.5%

S≤

0.030%

P≤

0.040%,

Ti and B such that;

3.2%≤

Ti≤

7.5%

(0.45×

Ti)−

1.35≤

B≤

(0.45×

Ti)−

0.43

optionally one or more elements chosen amongst;

Ni≤

1%

Mo≤

1%

Cr≤

3%

Nb≤

0.1%

V≤

0.1%

a remainder being iron and unavoidable impurities resulting from smelting,

the steel sheet having a structure consisting of ferrite, at most 10% of austenite, and precipitates, the precipitates comprising eutectic precipitates of TiB₂, a volume fraction of TiB₂ precipitates with respect to a whole structure being at least 9%, a percentage of TiB₂ precipitates having a surface area lower than 8 μ

m² being at least 96%.

2. The steel sheet according to claim 1, wherein a percentage of TiB₂ precipitates having a surface area lower than 3 μ

m² is at least 80%.

3. The steel sheet according to claim 1, wherein a percentage of TiB₂ precipitates having a surface area lower than 25 μ

m² is 100%.

4. The steel sheet according to claim 1, wherein in a core region of the steel sheet, a percentage of TiB₂ precipitates having a surface area lower than 8 μ

m² is of at least 96%.

5. The steel sheet according to claim 4, wherein in the core region of the steel sheet, a percentage of TiB₂ precipitates having a surface area lower than 3 μ

m² is at least 80%.

6. The steel sheet according to claim 4, wherein in the core region of the steel sheet, a percentage of TiB₂ precipitates having a surface area lower than 25 μ

m² is 100%.

7. The steel sheet according to claim 1, wherein the steel sheet comprises TiC precipitates with a volume fraction of 0.5% or lower.

8. The steel sheet according to claim 1, wherein the steel sheet comprises no Fe₂B precipitates.

9. The steel sheet according to claim 1, wherein the titanium, boron and manganese contents are such that:

(0.45×

Ti)−

1.35≤

B≤

(0.45×

Ti)−

0.43

and (0.45×

Ti)−

1.35≤

B≤

(0.45×

Ti)−

(0.261×

Mn)−

0.414.

10. The steel sheet according to claim 1, wherein the titanium and boron contents are such that:

(0.45×

Ti)−

1.35≤

B≤

(0.45×

Ti)−

0.50.

11. The steel sheet according to claim 1, wherein the composition is such that 0.010%≤

C≤

0.050%.

12. The steel sheet according to claim 1, wherein the composition is such that 0.005%≤

Al≤

1.3%.

13. The steel sheet according to claim 1, wherein the steel sheet has a Charpy energy Kcv of at least 25 J/cm² at −

40°

C.

14. The steel sheet according to claim 1, wherein the steel sheet has a content in free Ti of at least 0.95% and less than 3%.

15. A method for manufacturing a structural part, the method comprising:

cutting at least one blank from the steel sheet according to claim 1, and

deforming the blank within a temperature range from 20°

C. to 900°

C.

16. The method according to claim 15, comprising, before deforming the blank, a step of welding the blank to another blank.

17. A structural part comprising at least a portion made of a steel having a composition comprising, by weight percent:

0.010%≤

C≤

0.080%

0.06%≤

Mn≤

3%

Si≤

1.5%

0.005%≤

Al≤

1.5%

S≤

0.030%

P≤

0.040%,

Ti and B such that;

3.2%≤

Ti≤

7.5%

(0.45×

Ti)−

1.35≤

B≤

(0.45×

Ti)−

0.43

optionally one or more elements chosen amongst;

Ni≤

1%

Mo≤

1%

Cr≤

3%

Nb≤

0.1%

V≤

0.1%

a remainder being iron and unavoidable impurities resulting from smelting,

the portion having a structure consisting of ferrite, at most 10% of austenite, and precipitates, the precipitates comprising eutectic precipitates of TiB₂, a volume fraction of TiB₂ precipitates with respect to a whole structure of the portion being at least 9%, a percentage of TiB₂ precipitates having a surface area lower than 8 μ

m² being at least 96%.