Sheave member for belt-type continuously variable transmission and method of manufacturing the same

A method of manufacturing a sheave member for a belt-type continuously variable transmission that is provided with a sheave including a shaft portion and a sheave portion, the sheave portion surrounding the shaft portion and presenting a conical sheave surface which contacts the belt and which is radially outward of the shaft portion, the method comprising:

• a forming step in which a steel material is forged to form an intermediate product having a conical sheave surface;
• a carburization step in which the intermediate product is carburized by heating the intermediate product in a carburization gas;
• a gradual cooling step in which the intermediate product, after completion of the carburization step, is cooled at a cooling speed slower than a speed at which the microstructure of the intermediate product undergoes a martensitic transformation;
• a step of high frequency heating only a selected portion of the surface of the intermediate product to be strengthened by quenching, rather than the entire intermediate product, the selected portion including the conical sheave surface;
• a quenching step in which the selectively heated portion of the intermediate product is quenched by contact with water;
• and
• a finishing step in which the intermediate product is finished by a grinding to a final shape.