Abstract
The authors investigated the influences of difference in hardness of mating gears and their roughnesses on the surface durability, using hobbed gears (gear ratio 1:1) and rollers with various roughnesses. It is found that the pitting life of hobbed gears with combination of unequal hardnesses is shorter than that of ones with equal hardnesses. And, it is considered that the surface of softer steel is damaged by the surface asperities of harder steel when the initial roughness is large. furthermore, form the results of roller tests, it is found that the hardness increases at the surface of softer steel with the number of cycles. This fact is critical for the initiation of fatigue cracks. Therefore, in the case of HB≈340 (hardened and tempered) steel, it is clear that pitting is much influenced by the relationship between difference in hardness and initial surface roughness.
