Nippon Steel Corporation

Usui Co., Ltd.

Tsugumi Yamazaki

Taizo Makino

Tatsuya Masuda

Katsunori Nagao

Masahiro Yamazaki

Hiroaki Kondo

Tsutomu Okuyama

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

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Shizuoka, Japan

Tsugumi Yamazaki