To provide a pinion shaft in which breakage is hard to occur even if flaking is caused therein.
In the method for producing a shaft, a raw material is composed of an alloy steel having a carbon (C) content of, by weight, 0.9 to 1.5%, a chromium (Cr) content of 0.9 to 1.2%, a silicon (Si) content of 0.4 to 0.8%, a manganese (Mn) content of 0.9 to 1.2%, and the balance iron with inevitable impurities. Then, quenching and tempering are performed without carrying out treatment of introducing nitrogen into a surface layer part, thus the hardness of the surface layer part is controlled to ≥700 by Vickers hardness (Hv), the hardness of the core part is controlled to ≤260 by Vickers hardness (Hv), the content of retained austenite in the surface layer part is controlled to 15 to 50 vol.%, and the content of austenite in the core part is controlled to zero.
Yoshiaki Naito
Cui Shu Tetsu