Nippon Steel Corporation

Usui Co., Ltd.

Nippon Steel Sumitomo Metal Corporation

Usui Kokusai Sangyo Kaisha Limited

Tsutomu Okuyama

Hisashi Amaya

Hideki Takabe

Taizo Makino

Daisuke Matsuo

Tatsuya Masuda

Katsunori Nagao

Tsugumi Yamazaki

Takuji Nakahata

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 bar for a downhole member is provided that is excellent in SCC resistance and SSC resistance. A martensitic stainless steel bar material for a downhole member of the present embodiment has a chemical composition that contains, by mass %, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.01% or less, Cu: 0.10 to 2.50%, Cr: 10 to 14%, Ni: 1.5 to 7.0%, Mo: 0.2 to 3.0%, Ti: 0.05 to 0.3%, V: 0.01 to 0.10%, Nb: 0.1% or less, Al: 0.001 to 0.1% and N: 0.05% or less, with the balance being Fe and impurities, and satisfies Formula (1) and Formula (2).[Mo]&#x2212;4&#xd7;[total Mo amount in precipitate at R/2 position]&#x2265;1.30&#x2003;&#x2003;(1)[Total Mo amount in precipitate at center position]&#x2212;[total Mo amount in precipitate at R/2 position]&#x2264;0.03&#x2003;&#x2003;(2)

Steel bar for downhole member, and downhole member

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Tokyo, Japan

Tsutomu Okuyama