# US 10,308,995 B2 · Steel sheet having very high mechanical properties of strength and ductility

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- Number: US 10,308,995 B2
- Document ID: US10308995B2
- Status: Granted
- Kind: B2
- Application number: 14/907,358
- Filed: 2014-07-24
- Published: 2016-06-09
- Granted: 2019-06-04
- Earliest claimed: 2013-07-24
- Assignees: ArcelorMittal
- Applicants: ArcelorMittal
- Inventors: Sebastien Allain; Jean-Christophe Hell
- Web page: https://patentgrep.com/patent/US10308995B2

## CPC

- C21D 9/46: for sheet metals
- B22D 7/00: Casting ingots, {e.g. from ferrous metals}(equipment for conveying molten metal B22D35/00)
- B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium}
- C21D 1/26: Methods of annealing
- C21D 6/004: {containing Cr and Ni}
- 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}
- 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 38/34: with more than 1.5% by weight of silicon
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C22C 38/58: with more than 1.5% by weight of manganese
- C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence)
- C23C 2/022: {by heating}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/12: Aluminium or alloys based thereon
- C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath
- C23C 2/40: Plates; Strips
- 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)
- B22D: CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES (shaping of plastics or substances in a plastic state B29C; metallurgical processing, selection of substances to be added to metal C21, C22)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- 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)

## Abstract

The invention relates to the manufacture of a cold-rolled steel sheet having a strength of more than 900 MPa, an elastic limit of more than 700 MPa and distributed elongation of more than 12%, the composition of which includes, the contents being expressed as weight percentages: 0.26%≤C≤0.45%, 1.0%≤Mn≤3.0%, 1.0%≤Si≤3.0%, Al≤0.10%, 0%≤Cr≤1.5%, S≤0.005%, P≤0.020%, Nb≤0.1%, Ti≤0.020%, V≤0.015%, N≤0.01%, the remainder of the composition being iron and inevitable impurities resulting from the production process. The microstructure, given in surface proportions, comprises 13% to 25% residual austenite and 13% to 30% MA islands, the remainder consisting of bainite and possibly ferrite.

## Claims

### Claim 1

A cold-rolled and annealed steel sheet with mechanical strength greater than or equal to 900 MPa, an elastic limit greater than 700 MPa and uniform elongation greater than or equal to 12%, the composition of which comprises, expressed in percent by weight:
0.26%≤C≤0.45%;
1.0%≤Mn≤3.0%;
1.0%≤Si≤3.0%;
Al≤0.1%;
Cr≤1.5%;
S≤0.005%;
P≤0.020%;
Nb≤0.1%;
Ti≤0.02%;
V≤0.015%; and
N≤0.01%;
a balance of the composition including iron and unavoidable impurities resulting from processing;
256xC+47xMn+150xCr+2260xNb>142; and
a microstructure of the steel sheet including, in area percentages:
from 13 to 25% residual austenite; and
from 13 to 30% islands of residual austenite and martensite;
a balance of the microstructure including bainite formed at a temperature from 360 to 440 degrees C.

### Claim 2 (depends on 1)

The steel sheet according to claim 1, wherein the balance of the microstructure includes ferrite.

### Claim 3 (depends on 1)

The steel sheet according to claim 1, wherein the composition includes, expressed in percent by weight, 0.26%≤C≤0.35%.

### Claim 4 (depends on 1)

The steel sheet according to claim 1, wherein the composition includes, expressed in percent by weight, 1.4%≤Mn≤2.6%.

### Claim 5 (depends on 1)

The steel sheet according to claim 1, wherein the composition includes, expressed in percent by weight, 1.4%≤Si≤1.8%.

### Claim 6 (depends on 1)

The steel sheet according to claim 1, wherein the composition includes, expressed in percent by weight, Cr≤0.5%.

### Claim 7 (depends on 1)

The steel sheet according to claim 1, wherein the composition includes, expressed in percent by weight, Nb≤0.05%.

### Claim 8 (depends on 2)

The steel sheet according to claim 2, wherein the microstructure includes a maximum of 30% ferrite.

### Claim 9 (depends on 1)

The steel sheet according to claim 1, wherein a total elongation is greater than 14%.

### Claim 10 (depends on 1)

The steel sheet according to claim 1, further comprising a zinc or zinc alloy coating.

### Claim 11 (depends on 1)

An automobile part comprising:
a cold-rolled and annealed steel sheet according to claim 1 formed into a part.

### Claim 12

A cold-rolled and annealed steel sheet with mechanical strength greater than or equal to 900 MPa, an elastic limit greater than 700 MPa and uniform elongation greater than or equal to 12%, the composition of which comprises, expressed in percent by weight:
0.26%≤C≤0.45%;
1.0%≤Mn≤3.0%;
1.0%≤Si≤3.0%;
Al≤0.1%;
Cr≤1.5%;
S≤0.005%;
P≤0.020%;
Nb≤0.1%;
Ti≤0.02%;
V≤0.015%; and
N≤0.01%;
a balance of the composition consisting of iron and unavoidable impurities resulting from processing;
256xC+47xMn+150xCr+2260xNb>142; and
a microstructure of the steel sheet including, in area percentages:
from 13 to 25% residual austenite; and
from 13 to 30% islands of residual austenite and martensite;
a balance of the microstructure consisting of bainite or bainite and ferrite, the bainite being formed at a temperature from 360 to 440 degrees C.

### Claim 13 (depends on 12)

The cold-rolled and anneal steel sheet according to claim 12, wherein the balance of the microstructures consists of bainite.

### Claim 14 (depends on 12)

The cold-rolled and anneal steel sheet according to claim 12, wherein the bainite is formed at a temperature from 360 to 440 degrees C.

### Claim 15 (depends on 12)

The cold-rolled and anneal steel sheet according to claim 12, wherein the bainite is upper bainite and does not include carbides.

### Claim 16 (depends on 1)

The steel sheet according to claim 1, wherein the bainite is upper bainite and does not include carbides.