| 摘要 |
A seamless steel tube comprising, in mass %, C: 0.30 to 0.50%, Si: 0.5% or less, Mn: 0.3 to 2.0%, P: 0.025% or less, S: 0.005% or less, Cr: 0.15 to 1.0%, Al: 0.001 to 0.05%, Ti: 0.005 to 0.05%, N: 0.02% or less, B: 0.0005 to 0.01% and O (oxygen): 0.0050% or less, wherein Beff defined in following equation (a) or (b) takes a value of 0.0001 or more, where Beff=B-10.8x(N-14xTi/47.9)/14 - - - (a) when Neff=N-14xTi/47.9>=0, and Beff=B - - - (b) when Neff=N-14xTi/47.9<0, thus enabling to provide seamless steel tubes having excellent cold workability, hardenability, toughness and torsion fatigue strength and being most suitable for hollow shaft blanks for use in making one-piece type hollow drive shafts as well.
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