HIGH ALLOY FOR OIL WELL USE

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Provided is a high alloy for oil well use, having high strength and exceptional hot workability and SCC resistance. This high alloy for oil well use contains, expressed in mass%, C : 0.03% or less, Si : 1.0% or less, Mn : 0.05-1.5%, P : 0.03% or less, S : 0.03% or less, Ni : 26.0-40.0%, Cr : 22.0-30.0%, Mo : at least 0.01% but less than 5.0%, Cu : 0.1-3.0%, Al : 0.001-0.30%, N : more than 0.05% but not more than 0.30%, O : 0.010% or less, Ag : 0.005-1.0%, Ca : 0-0.01%, Mg : 0-0.01%, and rare earth elements : 0-0.2%, with the remainder comprising Fe and impurities. The alloy satisfies the following expression (1) and expression (2), and has yield strength of 758 MPa or above. 5 × Cu + (1, 000 × Ag) 2 ≧ 40 (1) Cu + 6 × Ag - 500 × (Ca + Mg + REM) ≦ 3.5 (2) Here, the contained amounts (in mass%) are substituted for the element symbols in the expressions.