| abstract |
Provided is a steel material and an oil well steel pipe having excellent SSC resistance even under a high pressure H 2 S environment. The steel material according to the present invention is, by mass%, C: 0.15 to 0.45%, Si: 0.10 to 1.0%, Mn: 0.10 to 0.8%, P: 0.050% or less S: 0.010% or less, Al: 0.01 to 0.1%, N: 0.010% or less, Cr: 0.1 to 2.5%, Mo: 0.35 to 3.0%, Co: 0.05 to 2.0%, Ti: 0.003 to 0.040%, Nb: 0.003 to 0.050%, Cu: 0.01 to 0.50% and Ni: 0.01 to 0.01 It contains 0.50% and satisfies the following formula. The former austenite grain size of the microstructure is less than 5 μm and the block size is less than 2 μm. In total, it contains 90% by volume or more of tempered martensite and tempered bainite. C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) /15-Co/6+α≧0.70 (1) (3C + Mo + 3Co) / (3Mn + Cr) ≧ 1.0 (2) |