| 摘要 |
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/mm2 or 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 20μm is 20μm 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.
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