Attached is some old AGMA 411.02 data of root stress & contact stress vs load cycles for grade 2 aircraft spur/helical power gears. Suitable for carburized AMS 6265 (VIM-VAR 9310).
There is not much published fatigue data for Ferrium C61/C63/C64 alloys, since they are a fairly recent development. You can try downloading a datasheet for C61 from the Carpenter Technology website. It might include some limited tensile fatigue data.
My experience is mostly related to aircraft drives. For flight critical gears AMS 6509 (VIM-VAR C64) is now commonly used primarily for its high tempering temperature, which provides excellent performance in a loss-of-lube condition. The material is vacuum carburized (AMS 2759/7) and direct high-pressure gas quenched. Another benefit of C64 is its greater core strength vs X53/9310. Here is a paper that provides some limited bending fatigue data for C64.
The AGMA gear data I posted is suitable for carburized double-vacuum-melt quality 9310. To determine what value to use, you need to calculate your bending and contact stress levels at a specific load and number of cycles. This single composite load/cycle value is usually calculated using Miner's rule based on a load or mission spectrum.
