Patent ID: 8302309

Claim:
A method of producing a bearing device for a wheel, the bearing device including an inner member and an outer member rotatable relative to each other through a plurality of rolling elements, one of the inner member and the outer member being a component part, the method comprising: forming the component part by hot forging, wherein during or at the end of the hot forging of the component part, a portion of the component part is cooled by showering a coolant over the component part or by controlling a cooling speed and temperature, whereby a matrix of the component part represents a standard structure and a surface portion of the component part represents a non-standard structure, and wherein the non-standard structure is a mixed structure comprising at least two or more of the following structures a fine ferrite-pearlite structure which is obtained by showering a coolant over the component part to locally cool it and subsequently self-recuperating it; a fine ferrite-pearlite structure which is obtained by showering a coolant over the component part to locally cool it preceding the hot forging; a tempered martensite structure, which is obtained by at the end of the hot forging by partially cooling the component part down to a martensite start point or lower, followed by heat-recuperating and tempering; an upper bainite structure, which is obtained by cooling the component part down to a temperature about equal to the room temperature at a predetermined cooling speed at the end of the hot forging; and a lower bainite structure, which is obtained by cooling the component part down to a temperature about equal to the room temperature at a predetermined cooling speed at the end of the hot forging.