# US 12,000,364 B2 · Steel pipe for fuel injection pipe and fuel injection pipe using the same

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- Number: US 12,000,364 B2
- Document ID: US12000364B2
- Status: Granted
- Kind: B2
- Application number: 15/121,058
- Filed: 2015-02-23
- Published: 2016-12-22
- Granted: 2024-06-04
- Earliest claimed: 2014-02-25
- Assignees: Usui Co., Ltd.; Nippon Steel Corporation
- Applicants: Usui Kokusai Sangyo Kaisha, Ltd.; Nippon Steel & Sumitomo Metal Corporation
- Inventors: Tatsuya Masuda; Tsugumi Yamazaki; Taizo Makino; Katsunori Nagao; Tsutomu Okuyama
- Web page: https://patentgrep.com/patent/US12000364B2

## CPC

- F02M 55/02: Conduits between injection pumps and injectors {, e.g. conduits between pump and common-rail or conduits between common-rail and injectors}
- C21D 8/10: during manufacturing of tubular bodies
- C21D 9/14: wear-resistant or pressure-resistant pipes
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- 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 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/22: with molybdenum or tungsten
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- 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
- C21D 7/10: of the whole cross-section, e.g. of concrete reinforcing bars
- C21D 9/08: for tubular bodies or pipes
- C21D 2211/002: Bainite
- C21D 2211/008: Martensite
- F02M 2200/9061: Special treatments for modifying the properties of metals used for fuel injection apparatus, e.g. modifying mechanical or electromagnetic properties
- F02M: SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- 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)

## Abstract

A steel pipe has a composition consisting, by mass percent, of, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, Mn: 0.3 to 2.0%, Al: 0.005 to 0.060%, N: 0.0020 to 0.0080%, Ti: 0.005 to 0.015%, Nb: 0.015 to 0.045%, Cr 0 to 1.0%, Mo: 0 to 1.0%, Cu: 0 to 0.5%, Ni: 0 to 0.5%, V: 0 to 0.15%, and B: 0 to 0.005%, the balance being Fe and impurities. As impurities, contents are Ca: 0.001% or less, P: 0.02% or less, S: 0.01% or less, and O: 0.0040% or less. The micro-structure is tempered martensitic or tempered martensite and tempered bainite, in which a prior-austenite grain size number is 10.0 or more. Tensile strength is TS 800 MPa or higher. Critical internal pressure is [0.3′TS′a] or more, a=[(D/d)2−1]/[0.776′(D/d)2], D: pipe outer diameter (mm), d: pipe inner diameter (mm).

## Claims

### Claim 1

A steel pipe for fuel injection pipe having a chemical composition consisting, by mass percent, of
C: 0.12 to 0.27%,
Si: 0.05 to 0.40%,
Mn: 0.3 to 2.0%,
Al: 0.005 to 0.060%,
N: 0.0020 to 0.0080%,
Ti: 0.005 to 0.015%,
Nb: 0.015 to 0.045%,
Cr: 0 to 1.0%,
Mo: 0 to 1.0%,
Cu: 0 to 0.5%,
Ni: 0 to 0.5%,
V: 0 to 0.15%, and
B: 0 to 0.005%,
the balance being Fe and impurities, and
contents of Ca, P, S, and O in the impurities being
Ca: 0.0001 to 0.0007%,
P: 0.02% or less,
S: 0.01% or less, and
O: 0.0040% or less,
and having a metal micro-structure consisting of a tempered martensitic structure, or a mixed structure of tempered martensite and tempered bainite, in which a prior-austenite grain size number is 10.0 or more, wherein
the steel pipe has an outer diameter of 20 mm or less, an inner diameter 2.5 mm or more, a wall thickness of 1.5 mm or more, a tensile strength of 800 MPa or higher, and a critical internal pressure satisfying a following formula (i):
IP≥0.3×TS×α (i)
α=[(D/d)2−1]/[0.776×(D/d)2] (ii)
where, in the above formula (i), IP denotes a critical internal pressure (MPa), TS denotes a tensile strength (MPa), and α is a value represented by the above formula (ii), and where, in the above formula (ii), D denotes an outer diameter (mm) of the steel pipe for fuel injection pipe, and d denotes an inner diameter (mm) of the steel pipe for fuel injection pipe.

### Claim 2 (depends on 1)

The steel pipe for fuel injection pipe according to claim 1, wherein
the chemical composition contains, by mass percent,
one or more elements selected from
Cr: 0.2 to 1.0%,
Mo: 0.03 to 1.0%,
Cu: 0.03 to 0.5%,
Ni: 0.03 to 0.5%,
V: 0.02 to 0.15%, and
B: 0.0003 to 0.005%.

### Claim 3 (depends on 1)

The steel pipe for fuel injection pipe according to claim 1, wherein
the outer diameter and the inner diameter of the steel pipe satisfy a following formula (iii):
D/d≥1.5 (iii)
where, in the above formula (iii), D denotes the outer diameter (mm) of the steel pipe for fuel injection pipe, and d denotes the inner diameter (mm) of the steel pipe for fuel injection pipe.

### Claim 4 (depends on 1)

A fuel injection pipe comprising the steel pipe for fuel injection according to claim 1.

### Claim 5 (depends on 2)

The steel pipe for fuel injection pipe according to claim 2, wherein
the outer diameter and the inner diameter of the steel pipe satisfy a following formula (iii):
D/d≥1.5 (iii)
where, in the above formula (iii), D denotes the outer diameter (mm) of the steel pipe for fuel injection pipe, and d denotes the inner diameter (mm) of the steel pipe for fuel injection pipe.

### Claim 6 (depends on 2)

A fuel injection pipe comprising the steel pipe for fuel injection according to claim 2.

### Claim 7 (depends on 3)

A fuel injection pipe comprising the steel pipe for fuel injection according to claim 3.

### Claim 8 (depends on 5)

A fuel injection pipe comprising the steel pipe for fuel injection according to claim 5.