Power transmission shaft and constant velocity joint

The present invention relates to a power transmission shaft used in apparatuses such as automobiles and industrial machines to transmit torque via a constant velocity joint. The present invention also relates to a constant velocity joint used in apparatuses such as automobiles and industrial machines to transmit driving power. A power transmission shaft using the constant velocity joint is manufactured by applying induction hardening to graphite steel thereby to harden the surface layer and form a 2-phase structure of ferrite and martensite in the core thereof. The graphite steel contains 0.35 to 0.70% of C, 0.4 to 2.0% of Si, 0.3 to 1.5% of Mn, 0.025% or less S, 0.02% or less P, 0.01 to 0.1% of Al, 0.001 to 0.004% of B and 0.002 to 0.008% of N by weight as the basic components, with the rest comprising Fe and inevitable impurities.