# US 12,215,402 B2 · Hot-rolled steel sheet

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- Number: US 12,215,402 B2
- Document ID: US12215402B2
- Status: Granted
- Kind: B2
- Application number: 17/784,901
- Filed: 2020-12-15
- Published: 2023-01-05
- Granted: 2025-02-04
- Earliest claimed: 2019-12-23
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel Corporation
- Inventors: Genki Abukawa; Masafumi Azuma; Eisaku Sakurada; Shohei Yabu
- Web page: https://patentgrep.com/patent/US12215402B2

## CPC

- C21D 9/46: for sheet metals
- C23C 2/06: Zinc or cadmium or alloys based thereon
- 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 6/001: {containing Ni (C21D6/004 takes precedence)}
- C21D 6/002: {containing Cr (C21D6/004 takes precedence)}
- 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}
- 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 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- 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 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/24: with vanadium
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- C22C 38/38: with more than 1.5% by weight of manganese
- C22C 38/50: with titanium or zirconium
- C21D 1/26: Methods of annealing
- C21D 8/0263: {following hot rolling}
- C21D 2211/008: Martensite
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/58: with more than 1.5% by weight of manganese
- 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)
- 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)

## Abstract

This hot-rolled steel sheet has a predetermined chemical composition, a microstructure includes 80% or more of tempered martensite by a volume percentage and a remainder consisting of one or more of ferrite, pearlite, bainite, fresh martensite, and residual austenite, the tempered martensite includes 5×109 pieces/mm3 or more of precipitates containing Ti and having an equivalent circle diameter of 5 nm or less per unit volume, in a surface layer region that is a range from a surface to a 1/10 position of a sheet thickness, a sum of an average pole density of a crystal orientation group consisting of {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 6.0 or less, and a tensile strength is 980 MPa or more.

## Claims

### Claim 1

A hot-rolled steel sheet comprising, as a chemical composition, by mass %:
C: 0.02% to 0.12%;
Si: 0.01% to 2.00%;
Mn: 1.00% to 3.00%;
P: 0.100% or less;
S: 0.010% or less;
N: 0.010% or less;
Al: 0.005% to 1.000%;
Ti: 0.01% to 0.20%;
Nb: 0% to 0.10%;
V: 0% to 0.100%;
Ni: 0% to 2.00%;
Cu: 0% to 2.00%;
Cr: 0% to 2.00%;
Mo: 0% to 2.00%;
W: 0% to 0.100%;
B: 0% to 0.0100%;
REM: 0% to 0.0300%;
Ca: 0% to 0.0300%;
Mg: 0% to 0.0300%; and
a remainder of Fe and impurities,
wherein the chemical composition satisfies 0.10≤Ti+Nb+V≤0.45,
a microstructure includes 80% or more of tempered martensite by a volume percentage, a remainder consists of one or more of ferrite, pearlite, bainite, fresh martensite, and residual austenite,
the tempered martensite includes 5×109 pieces/mm3 or more of precipitates containing Ti and having an equivalent circle diameter of 5 nm or less per unit volume,
in a surface layer region that is a range from a surface to a 1/10 position of a sheet thickness, a sum of an average pole density of a crystal orientation group consisting of {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 6.0 or less, and
a tensile strength is 980 MPa or more.

### Claim 2 (depends on 1)

The hot-rolled steel sheet according to claim 1, comprising, as the chemical composition, by mass %, one or more selected from:
Nb: 0.01% to 0.10%;
V: 0.010% to 0.100%;
Ni: 0.01% to 2.00%;
Cu: 0.01% to 2.00%;
Cr: 0.01% to 2.00%;
Mo: 0.01% to 2.00%;
W: 0.005% to 0.100%;
B: 0.0005% to 0.0100%;
REM: 0.0003% to 0.0300%;
Ca: 0.0003% to 0.0300%; and
Mg: 0.0003% to 0.0300%.

### Claim 3 (depends on 1)

The hot-rolled steel sheet according to claim 1,
wherein the tempered martensite includes 5×1011 pieces/mm3 or more of the precipitates per unit volume, and
the tensile strength is 1180 MPa or more.

### Claim 4 (depends on 2)

The hot-rolled steel sheet according to claim 2,
wherein the tempered martensite includes 5×1011 pieces/mm3 or more of the precipitates per unit volume, and
the tensile strength is 1180 MPa or more.

### Claim 5 (depends on 1)

The hot-rolled steel sheet according to claim 1,
wherein a standard deviation of nanohardness at a ¼ position of the sheet thickness from the surface is 0.8 GPa or less.

### Claim 6 (depends on 2)

The hot-rolled steel sheet according to claim 2,
wherein a standard deviation of nanohardness at a ¼ position of the sheet thickness from the surface is 0.8 GPa or less.

### Claim 7 (depends on 3)

The hot-rolled steel sheet according to claim 3,
wherein a standard deviation of nanohardness at a ¼ position of the sheet thickness from the surface is 0.8 GPa or less.

### Claim 8 (depends on 4)

The hot-rolled steel sheet according to claim 4,
wherein a standard deviation of nanohardness at a ¼ position of the sheet thickness from the surface is 0.8 GPa or less.

### Claim 9 (depends on 1)

The hot-rolled steel sheet according to claim 1,
wherein a hot-dip galvanized layer is provided on the surface.

### Claim 10 (depends on 2)

The hot-rolled steel sheet according to claim 2,
wherein a hot-dip galvanized layer is provided on the surface.

### Claim 11 (depends on 3)

The hot-rolled steel sheet according to claim 3,
wherein a hot-dip galvanized layer is provided on the surface.

### Claim 12 (depends on 4)

The hot-rolled steel sheet according to claim 4,
wherein a hot-dip galvanized layer is provided on the surface.

### Claim 13 (depends on 5)

The hot-rolled steel sheet according to claim 5,
wherein a hot-dip galvanized layer is provided on the surface.

### Claim 14 (depends on 9)

The hot-rolled steel sheet according to claim 9,
wherein the hot-dip galvanized layer is a hot-dip galvannealed layer.

### Claim 15 (depends on 10)

The hot-rolled steel sheet according to claim 10,
wherein the hot-dip galvanized layer is a hot-dip galvannealed layer.

### Claim 16 (depends on 11)

The hot-rolled steel sheet according to claim 11,
wherein the hot-dip galvanized layer is a hot-dip galvannealed layer.

### Claim 17 (depends on 12)

The hot-rolled steel sheet according to claim 12,
wherein the hot-dip galvanized layer is a hot-dip galvannealed layer.

### Claim 18 (depends on 13)

The hot-rolled steel sheet according to claim 13,
wherein the hot-dip galvanized layer is a hot-dip galvannealed layer.

### Claim 19

A hot-rolled steel sheet comprising, as a chemical composition, by mass %:
C: 0.02% to 0.12%;
Si: 0.01% to 2.00%;
Mn: 1.00% to 3.00%;
P: 0.100% or less;
S: 0.010% or less;
N: 0.010% or less;
Al: 0.005% to 1.000%;
Ti: 0.01% to 0.20%;
Nb: 0% to 0.10%;
V: 0% to 0.100%;
Ni: 0% to 2.00%;
Cu: 0% to 2.00%;
Cr: 0% to 2.00%;
Mo: 0% to 2.00%;
W: 0% to 0.100%;
B: 0% to 0.0100%;
REM: 0% to 0.0300%;
Ca: 0% to 0.0300%;
Mg: 0% to 0.0300%; and
a remainder of Fe and impurities,
wherein the chemical composition satisfies 0.10≤Ti+Nb+V≤0.45,
a microstructure includes 80% or more of tempered martensite by a volume percentage, a remainder comprising one or more of ferrite, pearlite, bainite, fresh martensite, and residual austenite,
the tempered martensite includes 5×109 pieces/mm3 or more of precipitates containing Ti and having an equivalent circle diameter of 5 nm or less per unit volume,
in a surface layer region that is a range from a surface to a 1/10 position of a sheet thickness, a sum of an average pole density of a crystal orientation group comprising {211}<111> to {111}<112> and a pole density in a crystal orientation of {110}<001> is 6.0 or less, and
a tensile strength is 980 MPa or more.