# US 12,215,405 B2 · Hot-pressed member, cold-rolled steel sheet for hot pressing, and manufacturing methods therefor

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- Number: US 12,215,405 B2
- Document ID: US12215405B2
- Status: Granted
- Kind: B2
- Application number: 17/432,218
- Filed: 2020-01-17
- Published: 2022-06-16
- Granted: 2025-02-04
- Earliest claimed: 2019-02-21
- Assignees: Jfe Steel Corporation
- Applicants: Jfe Steel Corporation
- Inventors: Katsutoshi Takashima; Minoru Tanaka; Yoshie Obata; Michitaka Sakurai
- Web page: https://patentgrep.com/patent/US12215405B2

## CPC

- C21D 9/48: deep-drawing sheets
- 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 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 8/04: to produce plates or strips for drawing, e.g. for deep-drawing
- C21D 8/0426: {Hot rolling}
- C21D 8/0436: {Cold rolling}
- C21D 8/0463: {following hot rolling}
- 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 38/16: containing copper
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C22C 38/58: 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
- C21D 2211/001: Austenite
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/008: Martensite
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/40: Plates; Strips
- 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)

## Abstract

Provided is a hot-pressed member that combines both high strength of 1850 MPa or more in TS and excellent delayed fracture resistance. A hot-pressed member comprises: a predetermined chemical composition; a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% to 4.0%; a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer; and a tensile strength of 1850 MPa or more.

## Claims

### Claim 1

A hot-pressed member, comprising:
a chemical composition consisting of, in mass %,
C: 0.31% or more and less than 0.55%,
Si: 0.01% or more and 1.0% or less,
Mn: 1.0% or more and 2.5% or less,
P: 0.05% or less,
S: 0.005% or less,
Al: 0.01% or more and 0.50% or less,
N: 0.01% or less, and
Cu: 0.002% or more and 0.25% or less,
and optionally one or more one or more selected from the group consisting of
Mo: 0.005% or more and 0.35% or less,
Cr: 0.005% or more and 0.35% or less,
Nb: 0.001% or more and 0.05% or less,
Ti: 0.001% or more and 0.050% or less,
B: 0.0002% or more and 0.0050% or less,
Ca: 0.005% or less,
V: 0.05% or less,
Sb: 0.001% or more and 0.020% or less,
Ni: 0.50% or less, and
Sn: 0.50% or less,
with a balance consisting of Fe and inevitable impurities;
a microstructure in which a prior austenite average grain size is 8 μm or less, a volume fraction of martensite is 95% or more, and a volume fraction of granular carbide of 0.1 μm or more in grain size is 0.10% or more and 4.0% or less;
a Ni diffusion region of 2.0 μm or more in a depth direction in a surface layer; and
a tensile strength of 1850 MPa or more.

### Claim 2 (depends on 1)

The hot-pressed member according to claim 1, further comprising
a Ni-containing Zn or Zn alloy coating or plating layer at a surface thereof.

### Claim 3

A cold-rolled steel sheet for hot pressing, comprising:
a chemical composition consisting of, in mass %,
C: 0.31% or more and less than 0.55%,
Si: 0.01% or more and 1.0% or less,
Mn: 1.0% or more and 2.5% or less,
P: 0.05% or less,
S: 0.005% or less,
Al: 0.01% or more and 0.50% or less,
N: 0.01% or less, and
Cu: 0.002% or more and 0.25% or less,
and optionally one or more selected from the group consisting of
Mo: 0.005% or more and 0.35% or less,
Cr: 0.005% or more and 0.35% or less,
Nb: 0.001% or more and 0.05% or less,
Ti: 0.001% or more and 0.050% or less,
B: 0.0002% or more and 0.0050% or less,
Ca: 0.005% or less,
V: 0.05% or less,
Sb: 0.001% or more and 0.020% or less,
Ni: 0.50% or less, and
Sn: 0.50% or less,
with a balance consisting of Fe and inevitable impurities; and
a microstructure in which a volume fraction of granular carbide of 0.1 μm or more in grain size is 1.0% or more and 25% or less.

### Claim 4 (depends on 3)

The cold-rolled steel sheet for hot pressing according to claim 3, further comprising
a Ni-containing coating or plating layer of 0.5 μm or more in thickness, at a surface thereof.

### Claim 5 (depends on 4)

The cold-rolled steel sheet for hot pressing according to claim 4, wherein the Ni-containing coating or plating layer is a Ni-containing Zn or Zn alloy coating or plating layer.

### Claim 6 (depends on 3)

A manufacturing method for a cold-rolled steel sheet for hot pressing, comprising:
hot rolling a steel slab having the chemical composition according to claim 3 at a finisher delivery temperature of 840° C. or more and 950° C. or less, to obtain a hot-rolled steel sheet;
cooling the hot-rolled steel sheet to a cooling stop temperature of 700° C. or less at a primary average cooling rate of 55° C./s or more as primary cooling, thereafter cooling the hot-rolled steel sheet to a coiling start temperature of 650° C. or less at a secondary average cooling rate of 5° C./s or more and 60° C./s or less as secondary cooling, and thereafter subjecting the hot-rolled steel sheet to coiling and pickling;
cold rolling the hot-rolled steel sheet after the pickling, to obtain a cold-rolled steel sheet; and
heating the cold-rolled steel sheet to a soaking temperature of 550° C. or more and 680° C. or less at an average heating rate of 1° C./s or less, holding the cold-rolled steel sheet at the temperature for 60 min or more and 3000 min or less, and thereafter cooling the cold-rolled steel sheet to room temperature.

### Claim 7 (depends on 6)

The manufacturing method for a cold-rolled steel sheet for hot pressing according to claim 6, comprising
performing a coating or plating treatment on a surface of the cold-rolled steel sheet with a Ni-containing coating or plating.

### Claim 8 (depends on 3)

A manufacturing method for a hot-pressed member, comprising
heating the cold-rolled steel sheet for hot pressing according to claim 3 to a temperature range of 850° C. or more and 1000° C. or less, and thereafter hot pressing the cold-rolled steel sheet.

### Claim 9 (depends on 4)

A manufacturing method for a hot-pressed member, comprising
heating the cold-rolled steel sheet for hot pressing according to claim 4 to a temperature range of 850° C. or more and 1000° C. or less, and thereafter hot pressing the cold-rolled steel sheet.

### Claim 10 (depends on 5)

A manufacturing method for a hot-pressed member, comprising
heating the cold-rolled steel sheet for hot pressing according to claim 5 to a temperature range of 850° C. or more and 1000° C. or less, and thereafter hot pressing the cold-rolled steel sheet.