A comparison of rolling contact fatigue behaviour of 17NiCrMo6-4 case-hardened disc specimens and gears

A two-disc test rig employed to assess the contact fatigue performance of gear materials is presented. Tests were performed on both shot-peened and un-peened 17NiCrMo6-4 discs, designed to recreate the meshing conditions between the sun and planet gears of planetary gear sets in the wheel hubs of off-highway vehicles. The mechanisms leading to pitting damage in disc specimens are discussed. Disc specimens with the same slide-to-roll ratio as that of the sun gears exhibited similar crater morphology but had 44% higher capacity in terms of contact pressure. This difference was attributed to changes in the disc geometry due to wear and micropitting during the tests, which enhanced the conformity between the contact surfaces and thus reduced the contact pressure for a given applied load.