| 简介 |
PROBLEM TO BE SOLVED : To provide a seamless steel tube having a 125 ksi level yield strength and excellent low temperature toughness.
SOLUTION : The seamless steel tube contains, by mass%, C : 0.21 to 0.35%, Si : 0.10 to 0.50%, Mn : 0.05 to 1.00%, P : 0.025% or less, S : 0.010% or less, Al : 0.005 to 0.100%, N : 0.010% or less, Cr : 0.10 to 1.30%, Mo : 0.05 to 1.00%, Ti : 0.002 to 0.040% and V : 0 to 0.30%, Nb : 0 to 0.050%, B : 0 to 0.0050% and further Ca : 0.0010 to 0.0060% and/or rare earth elements : 0.0010 to 0.0060% and the balance Fe with impurities. A crystal grain size number of a prior austenite is 7.0 or more. The number of a specific sulfide-based inclusion with a major axis of 1 μm or more is 5000/100 μm2 or less and average aspect ratio sis 3.4 or less.
SELECTED DRAWING : Figure 1
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