# US 12,601,039 B2 · Ferritic stainless steel and method for producing same

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- Number: US 12,601,039 B2
- Document ID: US12601039B2
- Status: Granted
- Kind: B2
- Application number: 18/287,114
- Filed: 2022-08-24
- Published: 2024-06-20
- Granted: 2026-04-14
- Earliest claimed: 2021-08-24
- Assignees: Nippon Steel Stainless Steel Corporation
- Applicants: NIPPON STEEL Stainless Steel Corporation
- Inventors: Kohichi Tsuboi; Kazunari Imakawa; Shinichi Teraoka
- Web page: https://patentgrep.com/patent/US12601039B2

## CPC

- C22C 38/24: with vanadium
- C21D 6/00: Heat treatment of ferrous alloys
- C21D 6/004: {containing Cr and Ni}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {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 38/005: {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 38/22: with molybdenum or tungsten
- 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 38/52: with cobalt
- C22C 38/54: with boron
- C21D 2211/005: Ferrite
- 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)

## Abstract

The present invention has an object to provide a ferritic stainless steel having a broad range of suitable quenching temperature and a high hardness and excellent corrosion resistance after quenching and beautiful and useful as a material for martensitic stainless steel products and provide an industrially stable method for production. The ferritic stainless steel of the present invention is characterized by having a steel composition comprising, by mass %, C: 0.45% or more and 0.55% or less, Si: 0.10% or more and 1.00% or less, Mn: 0.1% or more and 1.0% or less, Cr: 12.0% or more and 15.0% or less, Ni: 0% or more and 1.0% or less, Mo: 0.50% or more and 0.80% or less, V: 0.10% or more and 0.20% or less, N: 0.015% or more and 0.100% or less, P: 0% or more and 0.040% or less, S: 0% or more and 0.030% or less, balance: Fe and impurities, having an average crystal grain size of a ferrite phase of 10 μm or less, and having carbides having a diameter of 1.5 μm or less of 0.8/μm2 or more.

## Claims

### Claim 1

A ferritic stainless steel
having a steel composition comprising, by mass %,
C: 0.45% or more and 0.55% or less,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and 1.0% or less,
Cr: 12.0% or more and 15.0% or less,
Ni: 0% or more and 1.0% or less,
Mo: 0.50% or more and 0.80% or less,
V: 0.10% or more and 0.20% or less,
N: 0.015% or more and 0.100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.030% or less, and
balance: Fe and impurities,
having an average crystal grain size of a ferrite phase of 10 μm or less, and
having carbides having a diameter of 1.5 μm or less of 0.8/μm2 or more.

### Claim 2 (depends on 1)

The ferritic stainless steel according to claim 1, wherein an occupancy ratio of the carbides having a diameter of 1.5 μm or less in a ferrite grain boundary length is 5.0% or more.

### Claim 3 (depends on 1)

The ferritic stainless steel according to claim 1, comprising,
instead of part of the Fe,
by mass %, one or more of
Al: 0.30% or less,
Nb: 0.070% or less,
B: 0.0030% or less,
Ti: 0.070% or less,
Sn: 0.12% or less,
Cu: 0.40% or less,
W: 1.000% or less,
Co: 0.500% or less,
Zr: 0.500% or less,
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Y: 0.1000% or less,
REM: 0.10% or less, and
Sb: 0.15% or less.

### Claim 4 (depends on 1)

A ferritic stainless steel sheet having a thickness of 0.4 to 6.0 mm, and having the features according to claim 1.

### Claim 5 (depends on 1)

A method for producing the ferritic stainless steel according to claim 1,
the method for producing the ferritic stainless steel comprising the steps of:
hot rolling a steel having a composition comprising, by mass %,
C: 0.45% or more and 0.55% or less,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and 1.0% or less,
Cr: 12.0% or more and 15.0% or less,
Ni: 0% or more and 1.0% or less,
Mo: 0.50% or more and 0.80% or less,
V: 0.10% or more and 0.20% or less,
N: 0.015% or more and 0.100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.030% or less, and
balance: Fe and impurities,
by a start temperature of 1150° C. or more and a finish temperature of 850° C. to 900° C. to obtain a hot rolled steel sheet,
then cooling the hot rolled steel sheet by a cooling rate of 0.07° C./s or more up to a temperature of 700° C. to 800° C., and,
after cooling, heating and holding the hot rolled steel sheet at a temperature of 700° C. to 800° C. for 20 minutes or more and 20 hours or less.

### Claim 6 (depends on 4)

A method for producing the ferritic stainless steel sheet according to claim 4,
the method for producing the ferritic stainless steel sheet comprising the steps of:
hot rolling a steel having a composition comprising, by mass %,
C: 0.45% or more and 0.55% or less,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and 1.0% or less,
Cr: 12.0% or more and 15.0% or less,
Ni: 0% or more and 1.0% or less,
Mo: 0.50% or more and 0.80% or less,
V: 0.10% or more and 0.20% or less,
N: 0.015% or more and 0.100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.030% or less, and
balance: Fe and impurities,
by a start temperature of 1150° C. or more and a finish temperature of 850° C. to 900° C. to obtain a hot rolled steel sheet,
then cooling the hot rolled steel sheet by a cooling rate of 0.07° C./s or more up to a temperature of 700° C. to 800° C.,
after cooling, heating and holding the hot rolled steel sheet at a temperature of 700° C. to 800° C. for 20 minutes or more and 20 hours or less,
pickling the hot rolled steel sheet after heating and holding,
cold rolling the pickled hot rolled steel sheet to obtain a cold rolled steel sheet, and
heat treating the cold rolled steel sheet at a temperature of 700° C. to 800° C.

### Claim 7 (depends on 2)

The ferritic stainless steel according to claim 2, comprising,
instead of part of the Fe,
by mass %, one or more of
Al: 0.30% or less,
Nb: 0.070% or less,
B: 0.0030% or less,
Ti: 0.070% or less,
Sn: 0.12% or less,
Cu: 0.40% or less,
W: 1.000% or less,
Co: 0.500% or less,
Zr: 0.500% or less,
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Y: 0.1000% or less,
REM: 0.10% or less, and
Sb: 0.15% or less.

### Claim 8 (depends on 2)

A ferritic stainless steel sheet having a thickness of 0.4 to 6.0 mm, and having the features according to claim 2.

### Claim 9 (depends on 3)

A ferritic stainless steel sheet having a thickness of 0.4 to 6.0 mm, and having the features according to claim 3.

### Claim 10 (depends on 7)

A ferritic stainless steel sheet having a thickness of 0.4 to 6.0 mm, and having the features according to claim 7.

### Claim 11 (depends on 1)

A method for producing the ferritic stainless steel according to claim 1,
the method for producing the ferritic stainless steel comprising the steps of:
hot rolling a steel having a composition comprising, by mass %,
C: 0.45% or more and 0.55% or less,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and 1.0% or less,
Cr: 12.0% or more and 15.0% or less,
Ni: 0% or more and 1.0% or less,
Mo: 0.50% or more and 0.80% or less,
V: 0.10% or more and 0.20% or less,
N: 0.015% or more and 0.100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.030% or less, and
balance:
Fe,
by mass %, one or more of
Al: 0.30% or less,
Nb: 0.070% or less,
B: 0.0030% or less,
Ti: 0.070% or less,
Sn: 0.12% or less,
Cu: 0.40% or less,
W: 1.000% or less,
Co: 0.500% or less,
Zr: 0.500% or less,
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Y: 0.1000% or less,
REM: 0.10% or less, and
Sb: 0.15% or less,
and impurities,
by a start temperature of 1150° C. or more and a finish temperature of 850° C. to 900° C. to obtain a hot rolled steel sheet,
then cooling the hot rolled steel sheet by a cooling rate of 0.07° C./s or more up to a temperature of 700° C. to 800° C., and,
after cooling, heating and holding the hot rolled steel sheet at a temperature of 700° C. to 800° C. for 20 minutes or more and 20 hours or less.

### Claim 12 (depends on 4)

A method for producing the ferritic stainless steel sheet according to claim 4, the method for producing the ferritic stainless steel sheet comprising the steps of:
hot rolling a steel having a composition comprising, by mass %,
C: 0.45% or more and 0.55% or less,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and 1.0% or less,
Cr: 12.0% or more and 15.0% or less,
Ni: 0% or more and 1.0% or less,
Mo: 0.50% or more and 0.80% or less,
V: 0.10% or more and 0.20% or less,
N: 0.015% or more and 0.100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.030% or less, and
balance:
Fe,
by mass %, one or more of
Al: 0.30% or less,
Nb: 0.070% or less,
B: 0.0030% or less,
Ti: 0.070% or less,
Sn: 0.12% or less,
Cu: 0.40% or less,
W: 1.000% or less,
Co: 0.500% or less,
Zr: 0.500% or less,
Ca: 0.0050% or less,
Mg: 0.0050% or less,
Y: 0.1000% or less,
REM: 0.10% or less, and
Sb: 0.15% or less,
and impurities,
by a start temperature of 1150° C. or more and a finish temperature of 850° C. to 900° C. to obtain a hot rolled steel sheet,
then cooling the hot rolled steel sheet by a cooling rate of 0.07° C./s or more up to a temperature of 700° C. to 800° C.,
after cooling, heating and holding the hot rolled steel sheet at a temperature of 700° C. to 800° C. for 20 minutes or more and 20 hours or less,
pickling the hot rolled steel sheet after heating and holding,
cold rolling the pickled hot rolled steel sheet to obtain a cold rolled steel sheet, and
heat treating the cold rolled steel sheet at a temperature of 700° C. to 800° C.