| 摘要 |
An outer ring (11), an inner ring (12) and a ball (13) serving as machine parts are each constituted of steel containing at least 0.60 mass % and not more than 1.50 mass % of carbon, at least 0.15 mass % and not more than 2.50 mass % of silicon, at least 0.30 mass % and not more than 1.50 mass % of manganese, and at least 0.20 mass % and not more than 2.00 mass % of chromium with the rest consisting of an impurity. A nitrogen concentration in surface layer portions (11B, 12B, 13B) under an outer ring rolling contact surface (11A), an inner ring rolling contact surface (12A) and a ball rolling surface (13A), each serving as a contact surface to be in contact with another part, is at least 0.3 mass %. An average quantity of residual austenite as a whole in each of the outer ring (11), the inner ring (12) and the ball (13) is not more than 20 volume %. |
