Patent ID: 7824106

Claim:
A bearing device for a wheel comprising an outer member having a plurality of rows of raceway surfaces on an inner periphery thereof, an inner member having raceway surfaces in opposed relation to said raceway surfaces, and rolling elements interposed between the plurality of rows of said raceway surfaces in opposed relation to each other, wherein said inner member includes a first inner member and a second inner member, said first inner member and said second inner member are coupled to each other by caulking said first inner member, and the wheel is rotatably supported on a vehicle body, a grain size number of an austenite grain of at least the caulked portion is not less than 6, a ferrite area ratio of said caulked first inner member is 10 to 30 volume %, and a particulate ferrite is included, and said inner member has the ferrite pearlite structure containing said austenite grain with dispersed particles of said particulate ferrite.