Nippon Steel Corporation

Takuji Nakahata

Hisashi Amaya

Hideki Takabe

Daisuke Matsuo

Tsutomu Okuyama

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)

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Tokyo, Japan

Takuji Nakahata