# US 2020/0399727 A1 · High-strength, hot-rolled flat steel product with high edge cracking resistance and, at the same time, high bake-hardening potential, and method for producing such a flat steel product

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- Number: US 2020/0399727 A1
- Document ID: US20200399727A1
- Status: Published application
- Kind: A1
- Application number: 16/772,586
- Filed: 2018-12-11
- Published: 2020-12-24
- Earliest claimed: 2017-12-15
- Assignees: Salzgitter Flachstahl GmbH
- Applicants: Salzgitter Flachstahl GmbH
- Inventors: INGWER DENKS; JOACHIM SCHÖTTLER; CHRISTIAN PELZ; PATRICK WITTELER
- Web page: https://patentgrep.com/patent/US20200399727A1

## CPC

- C21D 8/0226: {Hot rolling}
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- 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
- C22C 38/14: containing titanium or zirconium
- C22C 38/18: containing chromium
- C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence)
- C23C 2/0224: {Two or more thermal pretreatments}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/40: Plates; Strips
- C21D 6/005: {containing Mn}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 2211/001: Austenite
- C21D 2211/002: Bainite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- C21D 2211/009: Pearlite
- Y10T 428/12799: Next to Fe-base component [e.g., galvanized]
- 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)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A flat product of steel with yield strength ftp 0.2 of 660 to 820 MPa, BH2 value greater than 30 MPa, a hole expansion ratio greater than 30%, and a microstructure having a first main component at a proportion of at least 50%, including one or more individual components of ferrite, tempered bainite, and tempered martensite, each with less than 5% carbides, and a second main component at a proportion of 5% to 50%, including one or more individual components of martensite, residual austenite, bainite or perlite, with the steel having a following chemical composition (in weight %): C: 0.04 to 0.12; Si: 0.03 to 0.8; Mn: 1 to 2.5: P: max. 0.08; S: max. 0.01; N: max. 0.01; Al: up to 0.1; Ni+Mo; up to 0.5; Nb: up to 0.08; Ti: up to 0.2; Nb+Ti: min, 0.03; Cr: up to 0.6; the remainder being iron including unavoidable steel-associated elements.

## Claims

### Claim at position 1

-11. (canceled)

### Claim 12

A high-strength, hot-roiled flat steel product having high edge cracking resistance and made from a steel with an elasticity limit Rp0.2 of 660 to 820 MPa, a BH2 value of over 30 MPa, and a hole expansion ratio of over 30%, said steel having a microstructure comprised of two main components, with a first one of the main components of the microstructure provided at a proportion of at least 50% and including at least one individual component selected from the group consisting of ferrite, tempered bainite, and tempered martensite and having less than 5% carbides, and with a second one of the main components of the microstructure provided at a proportion of 5% to 50% and including at least one individual component selected from the group consisting of martensite, residual austenite, bainite, and perlite, said steel comprising a following chemical composition (in wt. %):
C: 0.04 to 0.12
Si: 0.03 to 0.8
Mn: 1 to 2.5
P: max. 0.08
S: max. 0.01
N: max. 0.01
Al: up to 0.1
Ni+Mo: up to 0.5
Nb: up to 0.08
Ti: up to 0.2
Nb+Ti: min. 0.03
Cr: up to 0.6,
with the remainder being iron including unavoidable steel-associated elements.

### Claim 13 (depends on 12)

The flat steel product of claim 12, wherein the steel contains (in wt %):
C: 0.04 to 0.08
Si: 0.03 to 0.4
Mn: 1.4 to 2.0
P: max. 0.08
S: max. 0.01
N: max. 0.01
Al: up to 0.1
Ni+Mo: up to 0.6
Nb: up to 0.08
Ti: up to 0.2
Nb+Ti: min. 0.03.

### Claim 14 (depends on 12)

The flat steel product of claim 12, wherein the steel contains (in wt. %):
C: 0.04 to 0.08
Si: 0.03 to 0.4
Mn: 1.4 to 2.0
P: max, 0.08
S: max. 0.01
N: max. 0.01
Al: up to 0.1
Ni+Mo: up to 0.5
Nb: up to 0.05
Ti: up to 0.15
Nb+Ti: min. 0.03.

### Claim 15 (depends on 12)

The flat steel product of claim 12, wherein the first main component of the microstructure is formed as a matrix, said second main component of the microstructure being embedded in the form of at least one island into the first main component of the microstructure.

### Claim 16 (depends on 15)

The flat steel product of claim 15, wherein the at least one island has a size of less than 2 μm.

### Claim 17 (depends on 15)

The flat steel product of claim 15, wherein the at least one island has a size of less than 1 μm.

### Claim 18 (depends on 12)

The flat steel product of claim 12, having a tensile strength Rm of 760 to 960 MPa and an elongation at fracture A8 of more than 10%.

### Claim 19 (depends on 12)

The flat steel product of claim 12, having a tensile strength Rm of 760 to 960 MPa and an elongation at fracture A8 of more than 12%.

### Claim 20 (depends on 12)

The flat steel product of claim 12, wherein the steel product is galvanized by hot-dipping or electrolytically or is coated metallically, inorganically or organically.

### Claim 21 (depends on 12)

The flat steel product of claim 12, wherein the second main component has a carbon content which on average is higher than a carbon content of the first main component.

### Claim 22 (depends on 12)

A method for producing a hot-rolled flat steel product as set forth in claim 12, said method comprising:
melting a steel melt containing (in wt. %):
C: 0.04 to 0.12
Si: 0.03 to 0.8
Mn: 1 to 2.5
P: max. 0.08
S: max. 0.01
N: max. 0.01
Al: up to 0.1
Ni+Mo: up to 0.5
Nb: up to 0.08
Ti: up to 0.2
Nb+Ti: min. 0.03
Cr: up to 0.6,
with the remainder being iron including unavoidable steel-associated elements;
casting the steel melt to form a slab or thin slab by a horizontal or vertical slab or thin slab casting process;
reheating the slab or thin slab to a temperature of 1050° C. to 1250° C.;
hot-rolling the slab or thin slab to form a hot strip;
rolling in a last rolling pass at a final rolling temperature of less than 950° C. and greater than Ar3;
reeling the hot strip at a reefing temperature of below 650° C.; and
annealing the hot strip above Ac1 and below Ac1+100° C. with an annealing time of 10 seconds to 10 minutes and an average cooling rate between an annealing temperature and 500° C. of 1 K/s to 150 K/s.

### Claim 23 (depends on 22)

The method of claim 22, further comprising intermediate heating of the slab or thin slab between individual rolling passes as the slab or thin slab undergoes hot-rolling.

### Claim 24 (depends on 22)

The method of claim 22, wherein the hot strip is reeled at a reeling temperature in a range of 450° C. to 600° C.

### Claim 25 (depends on 22)

The method of claim 22, wherein the hot strip undergoes an average cooling rate between the annealing temperature and 500° C. of 5 K/s to 20 K/s.

### Claim 26 (depends on 22)

The method of claim 22, further comprising hot-dip coating the hot strip directly after undergoing a cooling process at the average cooling rate to a cooling stop temperature in a continuous hot-galvanizing installation.

### Claim 27 (depends on 22)

The method of claim 22, wherein the hot strip is rolled with a final rolling temperature of greater than Ar1+50° C.

### Claim 28 (depends on 22)

The method of claim 22, wherein the slab or thin slab is hot-rolled to form the hot strip with a thickness of 1.5 mm to 8 mm.

### Claim 29 (depends on 22)

The method of claim 22, wherein the slab or thin slab is hot-rolled to form the hot strip with a thickness of 1.8 mm to 4.5 mm.