| 摘要 |
Provided is a low-alloy steel pipe for an oil well that has a yield stress of 965 MPa (140 ksi) or higher and that makes it possible to stably obtain excellent SSC resistance. The low-alloy steel pipe for an oil well is provided with a structure that comprises: a chemical composition that contains, in mass%, 0.40-0.65% of C, 0.05-0.50% of Si, 0.10-1.00% of Mn, 0.020% or less of P, 0.0020% or less of S, 0.15% or less of Cu, 0.40-1.50% of Cr, 0.50-2.50% of Mo, 0.05-0.25% of V, less than 0.01% of Ti, 0.01-0.2% of Nb, 0.010-0.100% of sol.Al, 0.006% or less of N, 0-0.0015% of B, 0-0.003% of Ca, and a remainder of Fe and unavoidable impurities; tempered martensite; and less than 2% by volume fraction of residual austenite. The crystal grain size number of former austenite grains in the structure is 9.0 or higher. Among the packet, block, and lath boundaries in the tempered martensite, the equivalent circular diameter of a sub-structure that is surrounded by boundaries having a crystal orientation difference of 15° or higher is 3 µm or less. |
