Microstructure evolution and very-high-cycle fatigue crack initiation behavior of a structural steel with two loading intermittence modes

The effects of fatigue loading intermittence on specimens manufactured on two locations in a railway wheel were experimentally investigated: (i) in the rim and (ii) web plate (WP). The specimens with 50 ms pause presented a substantially lower fatigue strength in comparison to those with 300 ms pause. The microstructure evolution indicated the occurrence of martensitic transformation and discontinuous dynamic recrystallization. Rim and WP show respective preference for crack initiation, i.e. inclusion or matrix. Slip on {1 1 0} and {1 1 2} plane families prevails in ferrite. The pearlitic lamellae aligned at 45 degrees relative to applied tension indicates that crack initiates and propagates along the ferrite-cementite interface due to stress concentration as a result of inhomogeneous deformation.