# US 12,180,570 B2 · Hot-rolled steel sheet

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- Number: US 12,180,570 B2
- Document ID: US12180570B2
- Status: Granted
- Kind: B2
- Application number: 17/413,824
- Filed: 2020-03-05
- Published: 2022-02-10
- Granted: 2024-12-31
- Earliest claimed: 2019-03-11
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel Corporation
- Inventors: Hiroshi Shuto; Genki Abukawa; Akifumi Sakakibara; Jun Ando; Tetsu Asato; Shota Endo
- Web page: https://patentgrep.com/patent/US12180570B2

## CPC

- C22C 38/16: containing copper
- C21D 1/02: Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
- 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 8/0263: {following hot rolling}
- C21D 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence)
- C21D 9/46: for sheet metals
- 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 38/10: containing cobalt
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/38: with more than 1.5% by weight of manganese
- B21B 2261/14: Roughness
- C21D 2211/002: Bainite
- C21D 2211/005: Ferrite
- 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)
- B21B: ROLLING OF METAL (auxiliary operations used in connection with metal-working operations covered in B21, see B21C; bending by rolling B21D; manufacture of particular objects, e.g. screws, wheels, rings, barrels, balls, by rolling B21H; pressure welding by means of a rolling mill B23K20/04)

## Abstract

A hot-rolled steel sheet according to the present invention has a predetermined chemical composition, in which, when a height profile of a surface of the hot-rolled steel sheet is measured in each of five measurement ranges in a rolling direction and a direction perpendicular to the rolling direction, a distance in a height direction from an average height position which is an average of a height position of a point having a highest height position and a height position of a recessed part which is a point having a lowest height position to the recessed part is indicated as R1 (μm) in each of the height profiles, and an average of heights of two measurement points away from the recessed part in the rolling direction or the direction perpendicular to the rolling direction by 5 μm is indicated as R2 (μm), an average value of radii of curvature r represented by Expression (1) is 10 μm or more, and a tensile strength of the hot-rolled steel sheet is 500 MPa or more. r=(25+|R2−R1|2)/2|R2−R1| . . . (1)

## Claims

### Claim 1

A hot-rolled steel sheet comprising, as a chemical composition, by mass %:
C: 0.030% to 0.250%;
Si: 0.05% to 2.50%;
Mn: 1.00% to 4.00%;
Sol. Al: 0.001% to 2.000%;
P: 0.100% or less;
S: 0.0200% or less;
N: 0.01000% or less;
Ti: 0% to 0.20%;
Nb: 0% to 0.20%;
B: 0% to 0.010%;
V: 0% to 1.0%;
Cr: 0% to 1.0%;
Mo: 0% to 1.0%;
Cu: 0% to 1.0%;
Co: 0% to 1.0%;
W: 0% to 1.0%;
Ni: 0% to 1.0%;
Ca: 0% to 0.01%;
Mg: 0% to 0.01%;
REM: 0% to 0.01%;
Zr: 0% to 0.01%; and
a remainder comprising Fe and impurities,
wherein, when a height profile of a surface of the hot-rolled steel sheet is measured in each of five measurement ranges in a rolling direction and a direction perpendicular to the rolling direction, a distance in a height direction from an average height position which is an average of a height position of a point having a highest height position and a height position of a recessed part which is a point having a lowest height position to the recessed part is indicated as R1 (μm) in each of the height profiles, and a distance in a height direction from the average height position to an average of height positions of two measurement points away from the recessed part in the rolling direction or the direction perpendicular to the rolling direction by 5 μm is indicated as R2 (μm), an average value of radii of curvature r represented by Expression (1) is 10 μm or more,
a tensile strength of the hot-rolled steel sheet is 500 MPa or more, and
when the recessed part in which the R1 is 10 μm or more is referred to as a scale damage portion, an area ratio of the scale damage portion is 30% or less,
r=(25+|R2−R1|2)/2|R2−R1| (1).

### Claim 2 (depends on 1)

The hot-rolled steel sheet according to claim 1 comprising at least one of, as the chemical composition, by mass %:
Ti: 0.001% to 0.20%;
Nb: 0.001% to 0.20%;
B: 0.001% to 0.010%;
V: 0.005% to 1.0%;
Cr: 0.005% to 1.0%;
Mo: 0.005% to 1.0%;
Cu: 0.005% to 1.0%;
Co: 0.005% to 1.0%;
W: 0.005% to 1.0%;
Ni: 0.005% to 1.0%;
Ca: 0.0003% to 0.01%;
Mg: 0.0003% to 0.01%;
REM: 0.0003% to 0.01%; and
Zr: 0.0003% to 0.01%.