In order to apply a new u, material to the power transmission gears. the load-carrying capacity of the gear pairs with a combination of through-hardened steel (JIS SCM435) and as-cast spheroidal graphite cast iron ( FCD80 ) was s investigated by using a power circulating-type gear testing machine. The test results reveal that this combination of materials greatly influences the surface durability. The pinion (SCM35 ground gear) mating with a FCD80 hobbed gear operates better than that with a SCM435 hobbed gear. In the driven gears, the pitting fatigue life of FCD80 hobbed gears is longer than that of SCM435 hobbed gears or finish-hobbed gears. In the case of ground gears with a smooth tooth surface. the value of the endurance limit for the surface durability becomes greater in the FCD80 gears as well as in the SCM435 gears. From these considerations, it is found that gear pairs with a combination of SCM435 and FCD80 can be used for industrial gear units.
