Steel bar for downhole member, and downhole member
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]−4×[total Mo amount in precipitate at R/2 position]≥1.30 (1) [Total Mo amount in precipitate at center position]−[total Mo amount in precipitate at R/2 position]≤0.03 (2)
1. A steel bar for a downhole member, the steel bar having a diameter of 152.4 to 215.9 mm and having a chemical composition consisting of, 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,
N: 0.05 or less,
B: 0 to 0.005,
Ca: 0 to 0.008, and
Co: 0 to 0.5,
with the balance being Fe and impurities,
wherein:
when an Mo content in the chemical composition of the steel bar for a downhole member is defined as [Mo amount] (mass %), and an Mo content in precipitate at a position that bisects a line connecting a surface of the steel bar for a downhole member to a center of a cross-section perpendicular to a lengthwise direction of the steel bar for a downhole member is defined as [total Mo amount in precipitate at R/2 position] (mass %), the steel bar for a downhole member satisfies Formula (1), and
when an Mo content in precipitate at a center position in a cross-section perpendicular to the lengthwise direction of the steel bar for a downhole member is defined as [total Mo amount in precipitate at center position], the steel bar for a downhole member satisfies Formula (2);
[Mo amount]−4×[total Mo amount in precipitate at R/2 position]≤1.30 (1)
[Total Mo amount in precipitate at center position]−[total Mo amount in precipitate at R/2 position]≤0.03 (2).
2. The steel bar for a downhole member according to claim 1 ,
wherein the chemical composition contains, in lieu of a part of Fe, one or more elements selected from a group consisting of:
B: 0.0001 to 0.005 mass %, and
Ca: 0.0005 to 0.008 mass %.
3. The steel bar for a downhole member according to claim 1 ,
wherein the chemical composition contains, in lieu of a part of Fe:
Co: 0.05 to 0.5 mass %.
4. The steel bar for a downhole member according to claim 2 ,
wherein the chemical composition contains, in lieu of a part of Fe:
Co: 0.05 to 0.5 mass %.