Nippon Steel Corporation

Sumitomo Metal Industries, Inc.

Usui Co., Ltd.

Usui Kokusai Sangyo Kaisha Limited

Nippon Steel Sumitomo Metal Corporation

Katsunori Nagao

Taizo Makino

Tatsuya Masuda

Tsugumi Yamazaki

Masahiro Yamazaki

Kikuo Asada

Shoichiro Usui

Keisuke Hitoshio

Hiroaki Kondo

Tsutomu Okuyama

Osamu Endo

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)−1]/[0.776′(D/d)], D: pipe outer diameter (mm), d: pipe inner diameter (mm).

Steel pipe for fuel injection pipe and fuel injection pipe using the same

A steel pipe for fuel injection pipe has a tensile strength of 500 to 900 MPa and a yield ratio of 0.50 to 0.85, and has a critical internal pressure (IP) satisfying [IP&#x2265;0.41&#xd7;TS&#xd7;&#x3b1;] (&#x3b1;=[(D/d)&#x2212;1]/[0.776&#xd7;(D/d)], where TS: tensile strength (MPa) of the steel pipe, D: steel pipe outer diameter (mm), and d: steel pipe inner diameter (mm)), wherein a circumferential-direction residual stress on an inner surface of the pipe is &#x2212;20 MPa or lower after the steel pipe is split in half in a pipe axis direction.

Steel pipe for fuel injection pipe and method for producing the same

There is provided a steel pipe for fuel injection pipe that assures prolonged fatigue life and high reliability by securing a high critical internal pressure, at which fatigue fracture does not occur, while the material strength is high. A steel pipe for fuel injection pipe consisting of, by mass percent, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, and Mn: 0.8 to 2.0%, the balance being Fe and impurities, the impurities containing Ca: 0.001% or less, P: 0.02% or less, and S: 0.01% or less, wherein the tensile strength thereof is not lower than 900 N/mm, and the maximum diameter of a nonmetallic inclusion present during at least 20 &#x3bc;m depth from the inner surface of the steel pipe is not larger than 20 &#x3bc;m. Further, this steel pipe can contain one or more kinds of Cr: 1% or less, Mo: 1% or less, Ti: 0.04% or less, Nb: 0.04% or less, and V: 0.1% or less.

Manufacturing method for a steel pipe for fuel injection pipe

To provide a steel pipe as a fuel injection pipe with high material strength, high internal pressure limit free from fatigue failure, prolonged fatigue life, and high reliability. A steel pipe as a fuel injection pipe of 500 N/mmor higher tensile strength comprising, by mass, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, and Mn: 0.8 to 2.0%, and the balance being Fe and impurities, the contents of Ca, P, and S in the impurities being Ca: 0.001% or less, P: 0.02% or less, and S: 0.01% or less, respectively, characterized in that the maximum diameter of nonmetallic inclusions present in at least in a region extending from the inner surface of the steel pipe to a depth of 20 &#x3bc;m is 20 &#x3bc;m or less. Further, this steel pipe may contain, in place of a portion of Fe, at least one selected from among Cr: 1% or less, Mo: 1% or less, Ti: 0.04% or less, Nb: 0.04% or less, and V: 0.1% or less.

Steel pipe as fuel injection pipe

Growing community of inventors

Tokyo, Japan

Katsunori Nagao