Patent ID: 8070890

Claim:
An induction-hardened hollow driving shaft, comprising: as a raw material, a steel pipe that contains, by mass %, 0.30 to 0.47% C, 0.22% or less Si, 0.3 to 2.0% Mn, 0.018% or less P, 0.005% or less S, 0.15 to 1.0% Cr, 0.001 to 0.05% Al, 0.005 to 0.05% Ti, 0.004% or less Ca, 0.01% or less N, 0.0005 to 0.005% B, 0.0050% or less O (oxygen) and the balance Fe and impurities and of which Beff defined by an equation (a) or (b) below is 0.0001 or more, wherein a prior austenite grain size number (JIS G0551) after hardening is 9 or more, whereas, here with Ti, N and B each representing a content by %, in the case of Neff=Nâˆ’14Ã—Ti/47.9â‰§0, Beff=Bâˆ’10.8Ã—(Nâˆ’14Ã—Ti/47.9)/14â€ƒâ€ƒ(a), and similarly in the case of Neff=Nâˆ’14Ã—Ti/47.9<0, Beff=Bâ€ƒâ€ƒ(b).