| 摘要 |
A vehicle wheel bearing apparatus has an outer member formed, on its inner circumference, with double row outer raceway surfaces. An inner member includes a wheel hub integrally formed with a wheel mounting flange at its one end. The wheel hub outer circumference surface has double row inner raceway surfaces arranged opposite to the double row outer raceway surfaces. Double row balls are freely rollably contained between the outer raceway surfaces and inner raceway surfaces, respectively, of the outer member and the inner member. A pitch circle diameter of the double row ball group of the outer-side is larger than a pitch circle diameter of the double row ball group of the inner-side. At least the outer member and the wheel hub are formed of medium/high carbon steel including carbon of 0.40~0.80% by weight. The inner and outer raceway surfaces are formed, respectively, with predetermined hardened layers with a surface hardness of 58~64 HRC. The grain size number of austenite crystal grains of the metallographic structure in the hardened layers is selected larger than #7.
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