Steel gear and manufacturing method for the same

Abstract

A steel gearincludes a generally cylindrical outer peripheral ring portion, on an outer peripheral surfaceof which a toothed shapeis formed, and a flange portionprovided to extend radially inward from an inner peripheral surfaceof the outer peripheral ring portion. The outer peripheral ring portionincludes a first projecting portionthat projects toward one side in the axial direction with respect to a coupling position at which the first projecting portionis coupled to the flange portion, and a second projecting portionthat projects toward the other side in the axial direction with respect to a coupling position at which the second projecting portionis coupled to the flange portion. The axial length of the first projecting portionis longer than the axial length of the second projecting portion. The outer peripheral ring portionincludes a carburized layerformed in a surface layer of the toothed shape, and a thermal history layerformed in a region including the carburized layerand at a depth, in the inward direction from the outer peripheral surface, larger than the depth of the carburized layer, the thermal history layerhaving a history of being heated through high-frequency induction heating until becoming austenite. The depth T of the thermal history layerin the inward direction from a tooth bottomof the toothed shapeis larger at the second projecting portionthan at the first projecting portion