Patent ID: 8366322

Claim:
A shaft member for a fluid dynamic bearing device, comprising a recess for causing a dynamic pressure effect of a fluid in a bearing clearance, which is formed thereon by rolling, a surface layer portion of the recess and a surface layer portion of a surrounding region of the recess comprise a nitride layer, in which nitrogen is diffused and penetrated in a material of the shaft member, formed by nitriding after the rolling, a first work hardened layer that is a layer in which work hardening has been caused by the rolling is formed so as to overlap with an outermost surface layer portion of the nitride layer in the recess, and a second work hardened layer that is a layer in which work hardening has been caused by barreling is formed so as to overlap with an outermost surface layer portion of the nitride layer in the surrounding region of the recess, the hardness of an entire lower layer region of the surface layer portion is equal to or less than 400 Hv.