To provide a pinion shaft and a planetary gear device capable of elongating service life even when they are used under high temperature with high-speed rotation.
The pinion shaft 5 rotatably supporting a pinion gear 3 of the planetary gear device is fixed to a carrier 4 by caulking. The pinion shaft 5 is composed of high carbon chrome bearing steel. High frequency hardening treatment is performed only on a part of a rolling face, of an outer peripheral face of the pinion shaft 5, following carbonitriding treatment and annealing treatment, and further tempering treatment is performed. The amount of residual austenite on a surface layer portion of the pinion shaft 5 is 15 vol.% or more, and the amount of residual austenite of a core portion is 0 vol.%. Further at least a longitudinal end portion of the core portion has spheroidal cementite and pearlite structure. Further the hardness of the longitudinal end portion is Hv300 or less.
Yoshiaki Naito
Cui Shu Tetsu