PURPOSE: To obtain the title gear excellent in strength and vibration damping ability by integrating an outer ring made of nodular graphite cast iron on the tooth side and an inner ring made of flake graphite cast iron on the shaft hole side by fitting, and then austempering the integrated material under specified conditions.

CONSTITUTION: The gear is composed of the outer ring 1 and the inner ring 2, and a tooth 3 is provided to the periphery of the outer ring 1 and the shaft hole 4 to the inner periphery of the inner ring 2. The outer ring 1 is made of high-strength nodular graphite cast iron, and the inner ring 2 is made of the flake graphite cast iron having excellent vibration damping ability. The outer ring 1 and the inner ring 2 are integrated by fitting, and the integrated material is austempered into austenite at 850-950°C and then into bainite at 220-350°C. By this method, a gear wherein the strength and vibration damping ability are appropriately balanced is obtained. Furthermore, a mixed structure of bainite and residual austenite is obtained by the austempering, the interface between both structures contributes to the improvement of the vibration damping ability, and the vibration damping ability of the nodular graphite cast iron and the strength of the flake graphite cast iron are improved.