# US 10,480,043 B2 · Seamless steel pipe for line pipe and method for producing the same

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- Number: US 10,480,043 B2
- Document ID: US10480043B2
- Status: Granted
- Kind: B2
- Application number: 15/308,848
- Filed: 2015-05-12
- Published: 2017-03-09
- Granted: 2019-11-19
- Earliest claimed: 2014-05-16
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel & Sumitomo Metal Corporation
- Inventors: Yuji Arai; Yukimasa Ueda
- Web page: https://patentgrep.com/patent/US10480043B2

## CPC

- C21D 9/085: {Cooling or quenching}
- C21D 8/10: during manufacturing of tubular bodies
- C21D 9/08: for tubular bodies or pipes
- 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 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/22: with molybdenum or tungsten
- C22C 38/24: with vanadium
- C22C 38/28: with titanium or zirconium
- C22C 38/32: with boron
- C22C 38/38: with more than 1.5% by weight of manganese
- 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
- F16L 9/02: of metal (F16L9/16 - F16L9/22 take precedence)
- 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)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- F16L: PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL

## Abstract

A seamless steel pipe for line pipe has a chemical composition consisting, by mass percent, of C: 0.03-0.15%, Si: ≤0.50%, Mn: 1.0-2.0%, P: ≤0.050%, S: ≤0.005%, Cr: 0.1-1.0%, Al: 0.001-0.10%, N: ≤0.01%, Ni: 0.05-2.0%, B: 0.0003-0.0015%, Ca: 0.0002-0.0050%, Mo: 0.10-0.50%, Ti: 0.001-0.05%, Cu: 0-2.0%, Nb: 0-0.05%, V: 0-0.10%, the balance: Fe and impurities, and satisfying the conditions of 2Nb+4V+Mo≤0.50, wherein a metal micro-structure of the steel pipe contains 50% or more of bainite, in an area fraction, a wall thickness of the steel pipe is 25 mm or larger, and in a scale formed on the surface of the steel pipe, metal particles consisting mainly of Ni or Cu having an average circle-equivalent diameter of 0.1-5 mm exist. A distance from a boundary between the base metal of the steel pipe and the scale to a region in which the metal particles do not exist is 20 mm or longer.

## Claims

### Claim 1

A seamless steel pipe for line pipe having a chemical composition consisting, by mass percent, of
C: 0.03 to 0.15%,
Si: 0.50% or less,
Mn: 1.0 to 2.0%,
P: 0.050% or less,
S: 0.005% or less,
Cr: 0.1 to 1.0%,
Al: 0.001 to 0.10%,
N: 0.01% or less,
Ni: 0.05 to 2.0%,
B: 0.0003 to 0.0015%,
Ca: 0.0002 to 0.0050%,
Mo: 0.10 to 0.50%,
Ti: 0.001 to 0.05%,
Cu: 0 to 2.0%,
Nb: 0 to 0.05%,
V: 0 to 0.10%,
the balance: Fe and impurities, and
satisfying the following formula (i),
wherein a metal micro-structure of the steel pipe contains 50% or more of bainite, in an area fraction;
a wall thickness of the steel pipe is 25 mm or larger; and
in a scale formed on the surface of the steel pipe, metal particles consisting mainly of Ni or Cu having an average circle-equivalent diameter of 0.1 to 5 μm exist, and a distance from a boundary between the base metal of the steel pipe and the scale to a region in which the metal particles do not exist is 20 μm or longer:
2Nb+4V+Mo≤0.50 (i)
where each symbol of element in formula (i) represents the content (mass %) of each element.

### Claim 2 (depends on 1)

The seamless steel pipe for line pipe according to claim 1, wherein
the chemical composition contains, by mass percent,
one or more elements selected from
Cu: 0.01 to 2.0%,
Nb: 0.01 to 0.05%, and
V: 0.01 to 0.10%.

### Claim 3 (depends on 2)

The seamless steel pipe for line pipe according to claim 2, wherein at a position 10 μm distant from the boundary to the scale side, the number density of the metal particles observed per unit area is 5×103 pieces/mm2 or higher.

### Claim 4 (depends on 1)

The seamless steel pipe for line pipe according to claim 1, wherein at a position 10 μm distant from the boundary to the scale side, the number density of the metal particles observed per unit area is 5×103 pieces/mm2 or higher.

### Claim 5 (depends on 4)

A method for producing the seamless steel pipe for line pipe according to claim 4, wherein the steel pipe having the chemical composition consisting, by mass percent, of
C: 0.03 to 0.15%,
Si: 0.50% or less,
Mn: 1.0 to 2.0%,
P: 0.050% or less,
S: 0.005% or less,
Cr: 0.1 to 1.0%,
Al: 0.001 to 0.10%,
N: 0.01% or less,
Ni: 0.05 to 2.0%,
B: 0.0003 to 0.0015%,
Ca: 0.0002 to 0.0050%,
Mo: 0.10 to 0.50%,
Ti: 0.001 to 0.05%,
Cu: 0 to 2.0%,
Nb: 0 to 0.05%,
V: 0 to 0.10%,
the balance: Fe and impurities, and
satisfying the following formula (i),
is conveyed into a furnace after the finish of hot rolling, being heated in an atmosphere with the temperature of Ac3+50° C. or higher and the water vapor concentration of 5% or higher, and thereafter is subjected to quenching treatment in which accelerated cooling is performed at a rate of 10° C./s or higher, subsequently being tempered at a temperature of Ac1−50° C. or lower:
2Nb+4V+Mo≤0.50 (i)
where each symbol of element in formula (i) represents the content (mass %) of each element.

### Claim 6 (depends on 5)

The method for producing the seamless steel pipe for line pipe according to claim 5, wherein
the chemical composition contains, by mass percent,
one or more elements selected from
Cu: 0.01 to 2.0%,
Nb: 0.01 to 0.05%, and
V: 0.01 to 0.10%.

### Claim 7 (depends on 1)

A method for producing the seamless steel pipe for line pipe according to claim 1, wherein the steel pipe having the chemical composition consisting, by mass percent, of
C: 0.03 to 0.15%,
Si: 0.50% or less,
Mn: 1.0 to 2.0%,
P: 0.050% or less,
S: 0.005% or less,
Cr: 0.1 to 1.0%,
Al: 0.001 to 0.10%,
N: 0.01% or less,
Ni: 0.05 to 2.0%,
B: 0.0003 to 0.0015%,
Ca: 0.0002 to 0.0050%,
Mo: 0.10 to 0.50%,
Ti: 0.001 to 0.05%,
Cu: 0 to 2.0%,
Nb: 0 to 0.05%,
V: 0 to 0.10%,
the balance: Fe and impurities, and
satisfying the following formula (i),
is conveyed into a furnace after the finish of hot rolling, being heated in an atmosphere with the temperature of Ac3+50° C. or higher and the water vapor concentration of 5% or higher, and thereafter is subjected to quenching treatment in which accelerated cooling is performed at a rate of 10° C./s or higher, subsequently being tempered at a temperature of Ac1−50° C. or lower:
2Nb+4V+Mo≤0.50 (i)
where each symbol of element in formula (i) represents the content (mass %) of each element.

### Claim 8 (depends on 7)

The method for producing the seamless steel pipe for line pipe according to claim 7, wherein
the chemical composition contains, by mass percent,
one or more elements selected from
Cu: 0.01 to 2.0%,
Nb: 0.01 to 0.05%, and
V: 0.01 to 0.10%.