# US 10,501,830 B2 · High-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength hot-dip galvannealed steel sheet having excellent ductility, stretch-flangeability, and weldability

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- Number: US 10,501,830 B2
- Document ID: US10501830B2
- Status: Granted
- Kind: B2
- Application number: 15/128,410
- Filed: 2015-03-19
- Published: 2018-06-21
- Granted: 2019-12-10
- Earliest claimed: 2014-03-31
- Assignees: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)
- Applicants: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)
- Inventors: Michitaka Tsunezawa; Michiharu Nakaya
- Web page: https://patentgrep.com/patent/US10501830B2

## CPC

- C22C 38/14: containing titanium or zirconium
- 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 8/0273: {Final recrystallisation annealing}
- C21D 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence)
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- 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 38/16: containing copper
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- C22C 38/32: with boron
- C22C 38/38: 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 2/0224: {Two or more thermal pretreatments}
- C23C 2/024: {by cleaning or etching}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath
- C23C 2/40: Plates; Strips
- C21D 8/0236: {Cold rolling}
- C21D 9/46: for sheet metals
- C21D 2211/002: Bainite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- Y10T 428/12799: Next to Fe-base component [e.g., galvanized]
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- 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)
- 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

Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability in a range in which a tensile strength is 980 MPa or higher and a 0.2% yield strength is 700 MPa or higher. In the high-strength cold-rolled steel sheet of the present invention, the chemical composition is adjusted as appropriate, and the area ratio of below-mentioned metal structures at a position of ¼ sheet thickness in the steel sheet satisfies following requirements: tempered martensite: 30 area % or more, bainite: 15 area % to 70 area %, total of tempered martensite and bainite: 90 area % or more, ferrite: 0 area % to 5 area %, and retained austenite: 0 area % to 4 area %. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of 980 MPa or higher and a 0.2% yield strength of 700 MPa or higher.

## Claims

### Claim 1

A high-strength cold-rolled steel sheet with a tensile strength of 980 MPa or higher and a 0.2% yield strength of 700 MPa or higher,
the high-strength cold-rolled steel sheet comprising: in percent by mass,
C: 0.07% to 0.15%,
Si: 1.1% to 1.6%,
Mn: 2.0% to 2.8%,
P: more than 0% to 0.015%,
S: more than 0% to 0.005%,
Al: 0.015% to 0.06%,
Ti: 0.010% to 0.03%, and
B: 0.0010% to 0.004%,
with the balance being iron and inevitable impurities,
wherein
an area ratio of following metal structures at a position of ¼ sheet thickness in the steel sheet satisfies following requirements:
tempered martensite: 30 area % or more,
bainite: 15 area % to 70 area %,
total of tempered martensite and bainite: 90 area % or more,
ferrite: 0 area % to 5 area %, and
retained austenite: 0 area % to 2 area %,
an area ratio of following metal structures in a surface layer region at 20 μm in a sheet thickness direction from an outermost surface layer portion of the steel sheet satisfies following requirements:
ferrite: 80 area % or more, and
a total area ratio of martensite and bainite: 0 area % to 20 area %.

### Claim 2 (depends on 1)

The high-strength cold-rolled steel sheet according to claim 1, further comprising one or more selected from the group consisting of: in percent by mass,
Cu: more than 0% to 0.3%,
Ni: more than 0% to 0.3%,
Cr: more than 0% to 0.3%,
Mo: more than 0% to 0.3%,
V: more than 0% to 0.3%, and
Nb: more than 0% to 0.03%.

### Claim 3 (depends on 1)

The high-strength cold-rolled steel sheet according to claim 1, further comprising, in percent by mass, Ca: more than 0% to 0.005%.

### Claim 4 (depends on 2)

The high-strength cold-rolled steel sheet according to claim 2, further comprising, in percent by mass, Ca: more than 0% to 0.005%.

### Claim 5 (depends on 1)

A high-strength hot-dip galvanized steel sheet having a galvanized layer on a surface of the high-strength cold-rolled steel sheet according to claim 1.

### Claim 6 (depends on 1)

A high-strength hot-dip galvannealed steel sheet having a galvannealed layer on a surface of the high-strength cold-rolled steel sheet according to claim 1.