# US 11,898,219 B2 · Steel sheet

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- Number: US 11,898,219 B2
- Document ID: US11898219B2
- Status: Granted
- Kind: B2
- Application number: 17/604,720
- Filed: 2020-06-26
- Published: 2022-06-23
- Granted: 2024-02-13
- Earliest claimed: 2019-06-28
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel Corporation
- Inventors: Katsuya Nakano; Kengo Takeda; Hiroyuki Kawata; Akihiro Uenishi
- Web page: https://patentgrep.com/patent/US11898219B2

## CPC

- C21D 9/46: for sheet metals
- 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 1/02: Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
- C21D 1/185: {from an intercritical temperature}
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/007: {containing Co}
- C21D 6/008: {containing Si}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/021: involving particular fabrication steps or treatments of ingots or slabs
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 8/041: {involving a particular fabrication or treatment of ingot or slab}
- C21D 8/0426: {Hot rolling}
- C21D 8/0436: {Cold rolling}
- C21D 8/0463: {following hot rolling}
- C21D 8/0473: {Final recrystallisation annealing}
- C21D 9/48: deep-drawing sheets
- 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 38/008: {containing tin}
- 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 38/16: containing copper
- C22C 38/32: with boron
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/38: with more than 1.5% by weight of manganese
- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C25D 7/0614: {Strips or foils}
- C21D 2211/001: Austenite
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/008: Martensite
- C25D 5/50: by heat-treatment
- 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)
- 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)
- 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)
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR

## Abstract

A steel sheet including a steel micro-structure containing, in volume fraction, tempered martensite: 85% or more, retained austenite: 5% or more to less than 15%, and ferrite, pearlite, bainite, and as-quenched martensite being less than 10% in total, when contents of Mn and C in the retained austenite are denoted by MnA and CA, and when contents of Mn and C in a matrix are denoted by MnM and CM, respectively, following Formulas (1) to (3) are satisfied, and the number of carbides having an equivalent circle radius of 0.1 μm or more is 100 or less in a region measuring 20000 μm2, and the steel sheet has a tensile strength of 1100 MPa or more. The steel sheet is excellent in crash resistance and formability. MnA/MnM≥1.2 (1) CA/CM≤5.0 (2) CA≤1.0 (3)

## Claims

### Claim 1

A steel sheet including a steel micro-structure containing, in volume fraction,
tempered martensite: 85% or more, retained austenite: 5% or more to less than 15%, and ferrite, pearlite, bainite, and as-quenched martensite being less than 10% in total,
a chemical composition of the steel sheet consisting of, in mass %:
C: 0.18% or more to 0.38% or less,
Si: 0.80% or more to 2.50% or less,
Mn: 0.6% or more to 5.0% or less,
P: 0.0200% or less,
S: 0.0200% or less,
N: 0.0200% or less,
O: 0.0200% or less,
Al: 0% or more to 1.000% or less,
Cr: 0% or more to 2.0% or less,
Mo: 0% or more to 0.50% or less,
Ti: 0% or more to 0.10% or less,
Nb: 0% or more to 0.10% or less,
B: 0% or more to 0.0100% or less,
V: 0% or more to 0.50% or less,
Cu: 0% or more to 0.50% or less,
W: 0% or more to 0.100% or less,
Ta: 0% or more to 0.100% or less,
Ni: 0% or more to 1.00% or less,
Co: 0% or more to 0.50% or less,
Sn: 0% or more to 0.050% or less,
Sb: 0% or more to 0.050% or less,
As: 0% or more to 0.050% or less,
Mg: 0% or more to 0.050% or less,
Ca: 0% or more to 0.050% or less,
Y: 0% or more to 0.050% or less,
Zr: 0% or more to 0.050% or less,
La: 0% or more to 0.050% or less,
Ce: 0% or more to 0.050% or less, and
the balance: Fe and unavoidable impurities,
when a content of Mn and a content of C in the retained austenite are denoted by MnA and CA, respectively, and when a content of Mn and a content of C in a matrix are denoted by MnM and CM, respectively, following Formulas (1) to (3) are satisfied, and
when a region measuring 20000 μm2 and centered about a t/4 point (t denotes a thickness of the steel sheet) from a surface of the steel sheet is observed, the number of carbides having an equivalent circle radius of 0.1 μm or more is 100 or less, and the steel sheet has a tensile strength of 1100 MPa or more,
MnA/MnM≥1.2 (1)
CA/CM≤5.0 (2)
CA≤1.0 (3).

### Claim 2 (depends on 1)

The steel sheet according to claim 1 including a galvanized layer, a galvannealed layer, or an electrogalvanized layer on its surface.

### Claim 3

A steel sheet including a steel micro-structure containing, in volume fraction,
tempered martensite: 85% or more, retained austenite: 5% or more to less than 15%, and ferrite, pearlite, bainite, and as-quenched martensite being less than 10% in total,
a chemical composition of the steel sheet comprising in mass %:
C: 0.18% or more to 0.38% or less,
Si: 0.80% or more to 2.50% or less,
Mn: 0.6% or more to 5.0% or less,
P: 0.0200% or less,
S: 0.0200% or less,
N: 0.0200% or less,
O: 0.0200% or less,
Al: 0% or more to 1.000% or less,
Cr: 0% or more to 2.0% or less,
Mo: 0% or more to 0.50% or less,
Ti: 0% or more to 0.10% or less,
Nb: 0% or more to 0.10% or less,
B: 0% or more to 0.0100% or less,
V: 0% or more to 0.50% or less,
Cu: 0% or more to 0.50% or less,
W: 0% or more to 0.100% or less,
Ta: 0% or more to 0.100% or less,
Ni: 0% or more to 1.00% or less,
Co: 0% or more to 0.50% or less,
Sn: 0% or more to 0.050% or less,
Sb: 0% or more to 0.050% or less,
As: 0% or more to 0.050% or less,
Mg: 0% or more to 0.050% or less,
Ca: 0% or more to 0.050% or less,
Y: 0% or more to 0.050% or less,
Zr: 0% or more to 0.050% or less,
La: 0% or more to 0.050% or less,
Ce: 0% or more to 0.050% or less, and
the balance: Fe and unavoidable impurities,
when a content of Mn and a content of C in the retained austenite are denoted by MnA and CA, respectively, and when a content of Mn and a content of C in a matrix are denoted by MnM and CM, respectively, following Formulas (1) to (3) are satisfied, and
when a region measuring 20000 μm2 and centered about a t/4 point (t denotes a thickness of the steel sheet) from a surface of the steel sheet is observed, the number of carbides having an equivalent circle radius of 0.1 μm or more is 100 or less, and the steel sheet has a tensile strength of 1100 MPa or more,
MnA/MnM≥1.2 (1)
CA/CM≤5.0 (2)
CA≤1.0 (3).