# US 12,768,023 B2 · Steel sheet, member, and methods for manufacturing same

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- Number: US 12,768,023 B2
- Document ID: US12768023B2
- Status: Granted
- Kind: B2
- Application number: 18/683,839
- Filed: 2022-08-15
- Published: 2025-04-17
- Granted: 2026-10-20
- Earliest claimed: 2021-08-31
- Assignees: Jfe Steel Corporation
- Applicants: JFE Steel Corporation
- Inventors: Yoichiro Matsui; Tadachika Chiba; Shinjiro Kaneko; Akinori Nakamura
- Web page: https://patentgrep.com/patent/US12768023B2

## CPC

- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- 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 1/26: Methods of annealing
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 9/46: for sheet metals
- 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 38/008: {containing tin}
- C22C 38/02: containing silicon
- 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 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C22C 38/58: with more than 1.5% by weight of manganese
- B32B 2311/20: Zinc
- C21D 2211/001: Austenite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- 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)

## Abstract

Provided are a steel sheet; a related member; and methods for manufacturing the same. The steel sheet has a chemical composition including, in mass %, C: 0.06 to 0.25%, Si: 0.4 to 2.5%, Mn: 1.5 to 3.5%, P: 0.02% or less, S: 0.01% or less, sol. Al: less than 1.0%, and N: less than 0.015%, the balance being Fe and incidental impurities, the steel sheet being such that the steel sheet includes a steel microstructure including, in area fraction, polygonal ferrite: 10% or less (including 0%), tempered martensite: 40% or more, fresh martensite: 20% or less (including 0%), bainitic ferrite having 20 or less internal carbides per 10 μm2: 3 to 40%, and, in volume fraction, retained austenite: 5 to 20%, and the steel sheet has SC≥0.5/SC≥0.3×100 of 20% or more.

## Claims

### Claim 1

A steel sheet having a chemical composition comprising, in mass %:
C: 0.06 to 0.25%,
Si: 0.4 to 2.5%,
Mn: 1.5 to 3.5%,
P: 0.02% or less,
S: 0.01% or less,
sol. Al: less than 1.0%,
N: less than 0.015%,
and optionally,
one or two or more selected from the following groups A to C:
group A:
one or two selected from:
Ti: 0.1% or less, and
B: 0.01% or less,
group B:
one, or two or more selected from:
Cu: 1% or less,
Ni: 1% or less,
Cr: 1.0% or less,
Mo: 0.5% or less,
V: 0.5% or less,
Nb: 0.1% or less,
Zr: 0.2% or less, and
W: 0.2% or less,
group C:
one, or two or more selected from:
Ca: 0.0040% or less,
Ce: 0.0040% or less,
La: 0.0040% or less,
Mg: 0.0030% or less,
Sb: 0.1% or less, and
Sn: 0.1% or less,
the balance being Fe and incidental impurities,
the steel sheet being such that:
the steel sheet comprises a steel microstructure including, in area fraction,
polygonal ferrite: 10% or less,
tempered martensite: 40% or more,
fresh martensite: 20% or less,
bainitic ferrite having 20 or less internal carbides per 10 μm2: 3 to 40%, and, in volume fraction,
retained austenite: 5 to 20%, and
the steel sheet has a proportion SC≥0.5/SC≥0.3×100 of 20% or more wherein SC≥0.5 is the area of a region having a C concentration, in mass %, of 0.50% or more and SC≥0.3 is the area of a region having a C concentration, in mass %, of 0.30% or more.

### Claim 2 (depends on 1)

The steel sheet according to claim 1, wherein the steel microstructure has a number density of retained austenite present adjacent to the bainitic ferrite having 20 or less internal carbides per 10 μm2 of 50 or more per 10000 μm2.

### Claim 3 (depends on 1)

The steel sheet according to claim 1, wherein the steel sheet has a total elongation of 16.0% or more when TS is less than 1180 MPa, 14.0% or more when TS is 1180 MPa or more and less than 1320 MPa, and 13.0% or more when TS is 1320 MPa or more.

### Claim 4 (depends on 1)

The steel sheet according to claim 1, wherein the steel sheet has a hole expansion ratio of 30% or more.

### Claim 5 (depends on 1)

The steel sheet according to claim 1, which has a galvanized layer on a surface.

### Claim 6 (depends on 2)

The steel sheet according to claim 2, which has a galvanized layer on a surface.