# US 12,180,569 B2 · High-strength member, method for manufacturing high-strength member, and method for manufacturing steel sheet for high-strength member

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- Number: US 12,180,569 B2
- Document ID: US12180569B2
- Status: Granted
- Kind: B2
- Application number: 17/289,951
- Filed: 2019-09-25
- Published: 2022-01-13
- Granted: 2024-12-31
- Earliest claimed: 2018-10-31
- Assignees: Jfe Steel Corporation
- Applicants: Jfe Steel Corporation
- Inventors: Takuya Hirashima; Shimpei Yoshioka; Shinjiro Kaneko
- Web page: https://patentgrep.com/patent/US12180569B2

## CPC

- C22C 38/001: {containing N}
- C22C 38/02: containing silicon
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 9/46: for sheet metals
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- C21D 2211/002: Bainite
- C21D 2211/003: Cementite
- C21D 2211/008: Martensite
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- 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 high-strength member having excellent delayed fracture resistance, a method for manufacturing the high-strength member, and a method for manufacturing a steel sheet for the high-strength member. The high-strength member has a bent ridge portion obtained by using a steel sheet having a tensile strength of 1470 MPa or more, an edge surface of the bent ridge portion has a residual stress of 800 MPa or less, and a longest crack among cracks that extend from the edge surface of the bent ridge portion in a bent ridge direction D1 has a length of 10 μm or less.

## Claims

### Claim 1

A high-strength member formed from a steel sheet, the member comprising:
a bent ridge portion having an edge surface,
wherein:
the member has a tensile strength of 1470 MPa or more,
the edge surface of the bent ridge portion has a residual stress of 800 MPa or less,
a longest crack among cracks that extend from the edge surface of the bent ridge portion in a bent ridge direction has a length of 10 μm or less, and
the steel sheet has a chemical composition comprising, by mass %:
C: 0.17% or more and 0.35% or less;
Si: 0.001% or more and 1.2% or less;
Mn: 0.9% or more and 3.2% or less;
P: 0.02% or less;
S: 0.001% or less;
Al: 0.01% or more and 0.2% or less;
N: 0.010% or less; and
the balance being Fe and incidental impurities.

### Claim 2 (depends on 1)

The high-strength member according to claim 1, wherein the steel sheet has a microstructure including at least one of (i) bainite containing carbide grains having an average grain size of 50 nm or less and (ii) martensite containing carbide grains having an average grain size of 50 nm or less with a total area fraction of 90% or more based on an entire microstructure of the steel sheet.

### Claim 3 (depends on 2)

The high-strength member according to claim 2, wherein the chemical composition further comprises, by mass %, at least one Group selected from the group consisting of:
Group A: B: 0.0002% or more and less than 0.0035%,
Group B: at least one selected from the group consisting of Nb: 0.002% or more and 0.08% or less, and Ti: 0.002% or more and 0.12% or less,
Group C: at least one selected from the group consisting of Cu: 0.005% or more and 1% or less, and Ni: 0.005% or more and 1% or less,
Group D: at least one selected from the group consisting of Cr: 0.01% or more and 1.0% or less, Mo: 0.01% or more and less than 0.3%, V: 0.003% or more and 0.5% or less, Zr: 0.005% or more and 0.20% or less, and W: 0.005% or more and 0.20% or less,
Group E: at least one selected from the group consisting of Ca: 0.0002% or more and 0.0030% or less, Ce: 0.0002% or more and 0.0030% or less, La: 0.0002% or more and 0.0030% or less, and Mg: 0.0002% or more and 0.0030% or less, and
Group F: Sn: 0.002% or more and 0.1% or less.

### Claim 4 (depends on 1)

The high-strength member according to claim 1, wherein:
the steel sheet has a microstructure including at least one of (i) bainite containing carbide grains having an average grain size of 50 nm or less and (ii) martensite containing carbide grains having an average grain size of 50 nm or less with a total area fraction of 90% or more based on an entire microstructure of the steel sheet, and
the chemical composition further comprises, by mass %, Sb: 0.001% or more and 0.1% or less.

### Claim 5 (depends on 4)

The high-strength member according to claim 4, wherein the chemical composition further comprises, by mass %, at least one Group selected from the group consisting of:
Group A: B: 0.0002% or more and less than 0.0035%,
Group B: at least one selected from the group consisting of Nb: 0.002% or more and 0.08% or less, and Ti: 0.002% or more and 0.12% or less,
Group C: at least one selected from the group consisting of Cu: 0.005% or more and 1% or less, and Ni: 0.005% or more and 1% or less,
Group D: at least one selected from the group consisting of Cr: 0.01% or more and 1.0% or less, Mo: 0.01% or more and less than 0.3%, V: 0.003% or more and 0.5% or less, Zr: 0.005% or more and 0.20% or less, and W: 0.005% or more and 0.20% or less,
Group E: at least one selected from the group consisting of Ca: 0.0002% or more and 0.0030% or less, Ce: 0.0002% or more and 0.0030% or less, La: 0.0002% or more and 0.0030% or less, and Mg: 0.0002% or more and 0.0030% or less, and
Group F: Sn: 0.002% or more and 0.1% or less.

### Claim 6 (depends on 1)

The high-strength member according to claim 1, wherein the edge surface of the bent ridge portion has a residual stress of 600 MPa or less.

### Claim 7 (depends on 1)

The high-strength member according to claim 1, wherein the longest crack among cracks that extend from the edge surface of the bent ridge portion in the bent ridge direction has a length of 5 μm or less.

### Claim 8 (depends on 1)

The high-strength member according to claim 1, wherein the chemical composition comprises, by mass %, Mn: 1.8% or more and 3.2% or less.

### Claim 9 (depends on 1)

A method for manufacturing the high-strength member according to claim 1, the method comprising:
cutting out the steel sheet;
bending the steel sheet after the cutting;
subjecting an edge surface of the steel sheet formed by the cutting to a surface trimming before or after the bending; and
heating the edge surface of the steel sheet at a temperature of 270° C. or lower after the bending and the surface trimming.

### Claim 10 (depends on 2)

A method for manufacturing the high-strength member according to claim 2, the method comprising:
cutting out the steel sheet;
bending the steel sheet after the cutting;
subjecting an edge surface of the steel sheet formed by the cutting to a surface trimming before or after a bending; and
heating the edge surface of the steel sheet at a temperature of 270° C. or lower after the bending and the surface trimming.

### Claim 11 (depends on 4)

A method for manufacturing the high-strength member according to claim 4, the method comprising:
cutting out the steel sheet;
bending the steel sheet after the cutting;
subjecting an edge surface of the steel sheet formed by the cutting to a surface trimming before or after a bending; and
heating the edge surface of the steel sheet at a temperature of 270° C. or lower after the bending and the surface trimming.

### Claim 12 (depends on 3)

A method for manufacturing the high-strength member according to claim 3, the method comprising:
cutting out the steel sheet;
bending the steel sheet after the cutting;
subjecting an edge surface of the steel sheet formed by the cutting to a surface trimming before or after a bending; and
heating the edge surface of the steel sheet at a temperature of 270° C. or lower after the bending and the surface trimming.

### Claim 13 (depends on 5)

A method for manufacturing the high-strength member according to claim 5, the method comprising:
cutting out the steel sheet;
bending the steel sheet after the cutting;
subjecting an edge surface of the steel sheet formed by the cutting to a surface trimming before or after a bending; and
heating the edge surface of the steel sheet at a temperature of 270° C. or lower after the bending and the surface trimming.