# US 11,486,017 B2 · Cold rolled and annealed steel sheet, method of production thereof and use of such steel to produce vehicle parts

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- Number: US 11,486,017 B2
- Document ID: US11486017B2
- Status: Granted
- Kind: B2
- Application number: 16/302,977
- Filed: 2017-05-23
- Published: 2019-09-12
- Granted: 2022-11-01
- Earliest claimed: 2016-05-24
- Assignees: ArcelorMittal
- Applicants: Arcelormittal
- Inventors: Michel Soler; Ian Alberto Zuazo Rodriguez; Irène De Diego Calderon
- Web page: https://patentgrep.com/patent/US11486017B2

## CPC

- C21D 9/46: for sheet metals
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 1/26: Methods of annealing
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 8/0268: {between cold rolling steps}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 8/0284: {Application of a separating or insulating coating}
- C21D 8/0436: {Cold rolling}
- C21D 8/0468: {between cold rolling steps}
- C21D 8/0473: {Final recrystallisation annealing}
- C21D 8/0484: {Application of a separating or insulating coating}
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/12: Aluminium or alloys based thereon
- C21D 2211/001: Austenite
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/18: containing chromium
- Y02P 10/20: Recycling
- 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)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## 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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

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.

### Claim 4 (depends on 1)

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

### Claim 5 (depends on 3)

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

### Claim 6 (depends on 3)

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

### Claim 7 (depends on 1)

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

### Claim 8 (depends on 1)

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.

### Claim 9 (depends on 1)

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

### Claim 10 (depends on 4)

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

### Claim 11 (depends on 10)

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

### Claim 12 (depends on 1)

The cold rolled and twice annealed steel sheet according to claim 1, wherein the density is <7.1 g/cm3.

### Claim 13 (depends on 1)

The cold rolled and twice annealed steel sheet according to claim 1, wherein the density is <7 g/cm3.

### Claim 14 (depends on 1)

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/cm3.

### Claim 15 (depends on 1)

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

### Claim 16 (depends on 1)

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

### Claim 17 (depends on 15)

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

### Claim 18 (depends on 16)

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

### Claim 19 (depends on 1)

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.

### Claim 20 (depends on 19)

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.

### Claim 21 (depends on 19)

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

### Claim 22 (depends on 19)

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

### Claim 23 (depends on 21)

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

### Claim 24 (depends on 22)

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

### Claim 25 (depends on 19)

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