# US 2015/0147221 A1 · Low-Density Hot-or Cold-Rolled Steel, Method for Implementing Same and Use Thereof

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2015/0147221 A1
- Document ID: US20150147221A1
- Status: Published application
- Kind: A1
- Application number: 14/404,750
- Filed: 2013-05-27
- Published: 2015-05-28
- Earliest claimed: 2012-05-31
- Assignees: Arcelormitttal Investigacin Y Desarrollo, S.L.
- Applicants: Arcelormittal InvestigacióN Y Desarrollo, S.L.
- Inventors: Astrid Perlade; Ian Alberto Zuazo Rodriguez; Xavier Garat
- Web page: https://patentgrep.com/patent/US20150147221A1

## CPC

- C22C 38/14: containing titanium or zirconium
- B21B 1/463: {in a continuous process, i.e. the cast not being cut before rolling}
- B21B 45/0203: {Cooling}
- B21C 47/02: Winding-up or coiling
- C21D 6/005: {containing Mn}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0436: {Cold rolling}
- C21D 8/0473: {Final recrystallisation annealing}
- C21D 9/46: for sheet metals
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C21D 2211/001: Austenite
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/005: Ferrite
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- B21B: ROLLING OF METAL (auxiliary operations used in connection with metal-working operations covered in B21, see B21C; bending by rolling B21D; manufacture of particular objects, e.g. screws, wheels, rings, barrels, balls, by rolling B21H; pressure welding by means of a rolling mill B23K20/04)
- B21C: MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

A rolled steel sheet is provided. The rolled steel sheet has a mechanical strength greater than or equal to 600 MPa and an elongation at fracture that is greater than or equal to 20%. A a method for its fabrication is also provided. The chemical composition of the steel sheet includes 0.10≦C≦0.30%, 6.0≦Mn≦15.0%, 6.0≦Al≦15.0%, and optionally one or more elements selected from among: Si≦2.0%, Ti≦0.2%, V≦0.6% and Nb≦0.3%. The remainder of the composition includes iron and the unavoidable impurities resulting from processing. The ratio of the weight of manganese to the weight of aluminum is such that Mn Al > 1.0 . The microstructure of the sheet includes ferrite, austenite and up to 5% Kappa precipitates in area fraction.

## Claims

### Claim at position 1

1-22. (canceled)

### Claim 23

A rolled steel sheet having a density of less than or equal to 7.3 and a composition of which comprises the following elements, expressed in percent by weight:
0.10≦C≦0.30%;
6.0≦Mn≦15.0%; and
6.0≦Al≦15.0%,
the remainder of the composition being composed of iron and the unavoidable impurities caused by processing, wherein
Mn
Al
>
1.0
,
and a microstructure of the sheet consists of ferrite, austenite and up to 5% Kappa precipitates in area fraction.

### Claim 24 (depends on 23)

The steel sheet as recited in claim 23, wherein the composition comprises, expressed in percent by weight:
0.18≦C≦0.21%.

### Claim 25 (depends on 23)

The steel sheet as recited in claim 23, the composition of which comprises, expressed in percent by weight:
7.0≦Mn≦10.0%.

### Claim 26 (depends on 23)

The steel sheet as recited in claim 23, the composition of which comprises, expressed in percent by weight:
6.0≦Al≦12.0%.

### Claim 27 (depends on 23)

The steel sheet as recited in claim 23, the composition of which comprises, expressed in percent by weight:
6.0≦Al≦9.0%.

### Claim 28 (depends on 23)

The steel sheet recited in claim 23 further comprising at least one element, expressed as a percentage of weight, selected from:
Si≦2.0%;
Ti≦0.2%;
V≦0.6%; and
Nb≦0.3%.

### Claim 29 (depends on 28)

The steel sheet as recited in claim 28, the composition of which comprises, expressed in percent by weight:
Si≦1%.

### Claim 30 (depends on 29)

The steel sheet as recited in claim 29, wherein the area fraction of Kappa precipitates is less than or equal to 2%.

### Claim 31 (depends on 23)

The steel sheet as recited in claim 23, wherein a tensile mechanical strength is greater than or equal to 600 MPa and an elongation at fracture is greater than or equal to 20%.

### Claim 32 (depends on 23)

The steel sheet as recited in claim 23, wherein the ratio of the Mn content to the Al content is:
Mn
Al
≥
1.1
.

### Claim 33 (depends on 23)

The steel sheet as recited in claim 23, wherein the ratio of the Mn content to the Al content is:
Mn
Al
≥
1.5
.

### Claim 34 (depends on 23)

The steel sheet as recited in claim 23, wherein the ratio of the Mn content to the Al content of is:
Mn
Al
≥
2.0
.

### Claim 35 (depends on 23)

A method for fabricating a rolled steel sheet having a density less than or equal to 7.3, comprising the steps of:
providing a steel having the composition recited in claim 23;
casting the steel to form a semi-finished product;
rolling the semi-finished product with at least one rolling pass in the presence of ferrite to obtain a sheet, the final rolling temperature TFL being greater than or equal to 850° C.;
cooling the sheet at a cooling rate Vref1 to a coiling temperature Tbob which is less than or equal to 600° C.; and
coiling the cooled sheet.

### Claim 36 (depends on 35)

The method for fabricating a rolled steel sheet recited in claim 35 further comprising the step of reheating the semi-finished product to a temperature Trech between 1000° C. and 1280° C. before the rolling step.

### Claim 37 (depends on 35)

The method for fabricating a rolled sheet as recited in claim 35, wherein the semi-finished product is cast directly in the form of thin slabs or thin strips.

### Claim 38 (depends on 35)

The method for fabricating a rolled steel sheet as recited in claim 35, wherein the final rolling temperature TFL is between 900 and 980° C.

### Claim 39 (depends on 35)

The method for fabricating a rolled steel sheet as recited in claim 35, wherein the cooling rate Vref1 is less than or equal to 55° C./s.

### Claim 40 (depends on 35)

The method for fabricating a rolled steel sheet as recited in claim 35, the coiling temperature of which is between 450 and 550° C.

### Claim 41 (depends on 35)

The method for fabricating a rolled steel sheet as recited in claim 35, further comprising the steps of:
cold-rolling the steel sheet with a reduction rate between 35 and 90% to obtain a cold-rolled sheet; then
heating the cold-rolled sheet at a rate Vc to a hold temperature Tm between 800 and 950° C. for a length of time tm which is less than 600 seconds; then
cooling the sheet at a rate Vref2 to a temperature of less than or equal to 500° C.

### Claim 42 (depends on 41)

The method of fabricating a rolled steel sheet as recited in claim 41, wherein the temperature Tm is between 800 and 900° C.

### Claim 43 (depends on 41)

The method of fabricating a rolled steel sheet as recited in claim 41, wherein the cooling rate Vref2 is greater than or equal to 30° C./s.

### Claim 44 (depends on 41)

The method of fabricating a rolled steel sheet as recited in claim 41, wherein the cooling rate Vref2 is held at a temperature between 500° C. and 460° C.

### Claim 45 (depends on 41)

The method of fabricating a rolled steel sheet as recited in claim 41, further comprising the step of:
coating the sheet metal with zinc, a zinc alloy or a zinc-based alloy.

### Claim 46 (depends on 1)

A structural part or skin part for land motor vehicles comprising:
the rolled steel sheet recited in claim 1.

### Claim 47 (depends on 35)

A structural part or skin part for land motor vehicles made by the method recited in claim 35.

### Claim 48

A method for fabricating a rolled steel sheet having a density less than or equal to 7.3, comprising the steps of:
providing a steel having a composition comprising:
0.10≦C≦0.30%;
6.0≦Mn≦15.0%; and
6.0≦Al≦15.0%,
the remainder of the composition being composed of iron and the unavoidable impurities caused by processing, wherein
Mn
Al
>
1.0
,
and a microstructure of the sheet consists of ferrite, austenite and up to 5% Kappa precipitates in area fraction;
casting the steel to form a semi-finished product;
rolling the semi-finished product with at least one rolling pass in the presence of ferrite to obtain a sheet, the final rolling temperature TFL being greater than or equal to 850° C.;
cooling the sheet at a cooling rate Vref1 to a coiling temperature Tbob which is less than or equal to 600° C.; and
coiling the cooled sheet.