| abstract |
A thick-wall oil-well steel pipe which has a wall thickness of 40 mm or more, and has excellent SSC resistance and high strength (827 MPa or more), in which variation in strength in the wall-thickness direction is small is provided. The above described thick-wall oil-well steel pipe has a chemical composition containing, in mass%, C: 0.40 to 0.65%, Si: 0.05 to 0.50%, Mn: 0.10 to 1.0%, P: 0.020% or less, S: 0.0020% or less, sol. Al: 0.005 to 0.10%, Cr: more than 0.40 to 2.0%, Mo: more than 1.15 to 5.0%, Cu: 0.50% or less, Ni: 0.50% or less, N: 0.007% or less, and O: 0.005% or less. Further, the number of carbide which has a circle equivalent diameter of 100 nm or more and contains 20 mass% or more of Mo is 2 or less per 100µm 2 . Furthermore, the above described thick-wall oil-well steel pipe has yield strength of 827 MPa or more, and the difference between a maximum value and a minimum value of the yield strength in the wall-thickness direction is 45 MPa or less. |