| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength seamless steel tube for oil wells with an excellent sulfide-stress-cracking (SSC) resistance. <P>SOLUTION: The seamless steel tube has: a composition which contains, in terms of mass%, 0.15 to 0.50% of C, 0.1 to 1.0% of Si, 0.3 to 1.0% of Mn, 0.015% or less of P, 0.005% or less of S, 0.01 to 0.1% of Al, 0.01% or less of N, 0.1 to 1.7% of Cr, 0.40 to 1.1% of Mo, 0.01 to 0.08% of V, 0.01 to 0.08% of Nb, and 0.0005 to 0.003% of B, and 0.40% or more of Mo as solid solution Mo; and a metallographic structure having tempered martensite phase as a main phase and former austenite grains with a grain size number of 8.5 or above and dispersing 0.06 mass% or more of substantially particulate M<SB POS="POST">2</SB>C precipitates. In addition, it is possible to achieve further improvement of SSC resistance characteristics by providing densified regions of Mo on former γ grain boundaries and by setting a dislocation density to 6.0×10<SP POS="POST">14</SP>/m<SP POS="POST">2</SP>or less. <P>COPYRIGHT: (C)2012,JPO&INPIT |
