Patent ID: 6969201

Claim:
A wheel bearing device comprising: an outer member formed with double-row outer races on an inner periphery thereof; an inner member having a wheel hub having a flange for attachment of a wheel and a fitting member fitted to either one of an inner periphery and an outer periphery of the wheel hub, the inner member being formed with double-row inner races on an outer surface thereof, one of the wheel hub and the fitting member that is located inside being expanded radially outward by plastic deformation, thereby uniting the wheel hub and the fitting member; and double-row rollers interposed between the outer races and inner races, wherein at least one of the wheel hub and the fitting member is made of a steel material comprising iron, 0.5 to 0.7 weight % of carbon, 0.1 to 1.5 weight % of silicon, 0.6 to 1.0 weight % of manganese, and inevitable impurities, wherein said steel material has an austenite grain size number of 3 or more.