Thermal and thermochemical treatments against fretting failure applied to power transmissions

Abstract

Some power transmission components are subject to the fretting corrosion failure mode, which results in rapid wear of mating surfaces or premature fatigue crack initiation. Fretting corrosion is generated by micro-movements of surfaces in contact. In mechanical transmissions, it is found in particular on shrink-fit connections (bearing rings, for example) and on key and spline connections when they are misaligned or not with the well design fit.The sectoral board for mechanical transmissions and rolling bearings and CETIM is investigating the potential of technical solutions (materials, heat treatment, lubrication, etc.) to prevent fretting. This article presents a study of the impact of thermal and thermochemical heat treatments of steels used in power transmissions on the appearance, morphology and intensity of corrosion fretting.Among the materials and heat treatments commonly used in mechanical transmissions (NF EN 683, ISO 6336-5), the following variants were studied: through-hardened steels (42CrMo4, 100Cr6), surface-hardened steels (42CrMo4), case-hardened steels (20MnCr5) and nitrided steels (42CrMo4). These variants are compared using a standardized ASTM G204 test, which involves oscillating a pressurized, lubricant-free pin (100Cr6) on a plate (the tested variant) for 24 hours. The peak-to-peal slip amplitude range is set at 50µm or 100µm. Tangential forces during testing, then the volume loss of pin and plate after testing, were measured, analysed and compared. The experimental study reveals wear resistance and depend on heat and thermochemical treatment as well as slip amplitudes. Through hardened 100Cr6 has better fretting resistance than nitrided 42CrMo4 for 50µm amplitude, but the results are completely reversed at 100µm amplitude.