EA4T railway axle steel fatigue behavior under very high-frequency fatigue loading

One of the most loaded components of the train, with very long operation time, is a railway axle. During its operation, the conventional fatigue limit of 10(7) cycles is reached easily and information about fatigue behavior for a higher number of cycles is missing. Therefore, the fatigue behavior of railway axle EA4T heat-treated steel with a bainitic microstructure was examined under very high-frequency fatigue loading. S-N curve shift to the higher number of cycles at the same stress amplitude due to the testing frequency increase was observed. However, the same fatigue endurance limit of 375 MPa was determined for 10(7) cycles at a frequency of 120 Hz and for 10(10) cycles at a frequency of 20 kHz. Due to homogenous and fine bainitic structure in a whole tested volume of material, the same fatigue crack initiation and propagation mechanism was observed to be characteristic for all the tested specimens, regardless of the used testing frequency and stress amplitude. Surface and subsurface non-inclusion fatigue crack initiation was responsible for the failure of the specimens. Obtain results confirm, that fatigue endurance limit determined by traditional high fatigue test can be used also for several orders higher number of cycles.