# US 10,308,994 B2 · Seamless steel tube for fuel injection

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- Number: US 10,308,994 B2
- Document ID: US10308994B2
- Status: Granted
- Kind: B2
- Application number: 15/300,810
- Filed: 2015-03-20
- Published: 2017-01-26
- Granted: 2019-06-04
- Earliest claimed: 2014-04-03
- Assignees: Jfe Steel Corporation
- Applicants: JFE Steel Corporation
- Inventors: Yoshikazu Kawabata; Manabu Nishino; Makio Gunji
- Web page: https://patentgrep.com/patent/US10308994B2

## CPC

- C21D 9/14: wear-resistant or pressure-resistant pipes
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 1/28: Normalising
- C21D 7/02: by cold working
- C21D 8/10: during manufacturing of tubular bodies
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/06: containing aluminium
- C22C 38/58: with more than 1.5% by weight of manganese
- F02M 55/02: Conduits between injection pumps and injectors {, e.g. conduits between pump and common-rail or conduits between common-rail and injectors}
- F02M 61/166: {Selection of particular materials}
- C21D 9/08: for tubular bodies or pipes
- C21D 2211/001: Austenite
- F02M 2200/9053: Metals
- 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)
- F02M: SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF

## Abstract

A seamless steel tube has a particular composition and a structure with an average prior γ grain size of 150 μm or less in an axial cross-section after cold drawing and heat treatment. The structure retards the growth of a fatigue crack. The steel tube has a tensile strength TS of 500 MPa or more and good internal pressure fatigue resistance and is suitable for use as a fuel injection tube under high injection pressures. The composition of the steel tube may further contain at least one of Cu, Ni, Cr, Mo, and B; at least one of Ti, Nb, and V; and/or Ca.

## Claims

### Claim 1

A seamless steel tube for fuel injection having a composition comprising, by mass, 0.155% to 0.21% C, 0.01% to 0.49% Si, 1.20% to 2.1% Mn, 0.005% to 0.25% Al, and 0.0010% to 0.010% N and containing, as impurities, 0.030% or less P, 0.025% or less S, and 0.005% or less O, the balance being Fe and incidental impurities, the composition satisfying condition (1):
[Al %]×[N %]≤27×10−5 (1)
wherein Al % and N % are the contents (% by mass) of Al and N, respectively,
the steel tube having a structure with an average prior γ grain size of 150 μm or less in an axial cross-section after cold drawing and heat treatment, and
a tensile strength TS of 500 MPa or more.

### Claim 2 (depends on 1)

The seamless steel tube according to claim 1, wherein the composition further comprises, by mass, at least one of 0.70% or less Cu, 1.00% or less Ni, 1.20% or less Cr, 0.50% or less Mo, and 0.0060% or less B.

### Claim 3 (depends on 1)

The seamless steel tube according to claim 1, wherein the composition further comprises, by mass, at least one of 0.20% or less Ti, 0.050% or less Nb, and 0.20% or less V.

### Claim 4 (depends on 2)

The seamless steel tube according to claim 2, wherein the composition further comprises, by mass, at least one of 0.20% or less Ti, 0.050% or less Nb, and 0.20% or less V.

### Claim 5 (depends on 1)

The seamless steel tube according to claim 1, wherein the composition further comprises, by mass, 0.0040% or less Ca.

### Claim 6 (depends on 2)

The seamless steel tube according to claim 2, wherein the composition further comprises, by mass, 0.0040% or less Ca.

### Claim 7 (depends on 3)

The seamless steel tube according to claim 3, wherein the composition further comprises, by mass, 0.0040% or less Ca.

### Claim 8 (depends on 4)

The seamless steel tube according to claim 4, wherein the composition further comprises, by mass, 0.0040% or less Ca.