Oil-well steel pipe having excellent sulfide stress cracking resistance
View Patent ↗To provide an oil-well steel pipe having excellent SSC resistance. The oil-well steel pipe according to the present invention contains, by mass percent, C: 0.15 to 0.35%, Si: 0.1 to 0.75%, Mn: 0.1 to 1.0%, Cr: 0.1 to 1.7%, Mo: 0.1 to 1.2%, Ti: 0.01 to 0.05%, Nb: 0.010 to 0.030%, Al: 0.01 to 0.1%, P: at most 0.03%, S: at most 0.01%, N: at most 0.007%, and O: at most 0.01%, the balance being Fe and impurities. The Ti content and the Nb content in a residue obtained by bromine-methanol extraction satisfy equation (1): 100×[Nb]/([Ti]+[Nb])≦27.5 (1) where the Ti content (mass %) and the Nb content (mass %) in the residue are substituted for [Ti] and [Nb].
1. An oil-well steel pipe containing, by mass percent,
C: 0.15 to 0.35%,
Si: 0.1 to 0.75%,
Mn: 0.1 to 1.0%,
Cr: 0.1 to 1.7%,
Mo: 0.1 to 1.2%,
Ti: 0.01 to 0.05%
Nb: 0.010 to 0.030%, and
Al: 0.01 to 0.1%,
B: at most 0.0050%,
the balance being Fe and impurities, P, S, N and O in the impurities being
P: at most 0.03%,
S: at most 0.01%,
N: at most 0.007%, and
O: at most 0.01%,
wherein the Ti content and the Nb content in a residue obtained by bromine-methanol extraction satisfy equation (1):
100×[Nb]/([Ti]+[Nb])≦27.5 (1)
where the Ti content (mass %) and the Nb content (mass %) in the residue are substituted for [Ti] and [Nb],
the oil-well steel pipe has a yield strength of 654 MPa or more and a prior austenite grain size number of 7.5 or larger.
2. The oil-well steel pipe according to claim 1 , containing V: at most 0.50% in place of some part of Fe.
3. The oil-well steel pipe according to claim 1 , containing Ca: at most 0.0050% in place of some part of Fe.
4. The oil-well steel pipe according to claim 2 , containing Ca: at most 0.0050% in place of some part of Fe.
5. The oil-well steel pipe according to claim 1 , wherein the C content is 0.20 to 0.35 mass %.