An investigation about the influence of deep rolling on fatigue crack growth in railway axles made of a medium strength steel

•Tendency of crack growth curves and thresholds to overlap below R=−2.•No crack initiation for small flaws, unusual cracking for the largest ones.•Complex surface damage pattern around the tips of the initial notches.•Crack propagation happened for very high ΔKmax/ΔKth ratios.•No-interaction crack propagation models agree with experimental evidence. Over the last years, deep rolling has been adopted to improve the fatigue strength of railway axles, but very few scientific analyses and studies of this phenomenon are available in the literature. For this reason, the present research investigates some aspects related to the influence of this technological process on fatigue crack growth in railway axles made of EA4T steel grade. Firstly, special full-scale specimens were prepared applying the industrial deep-rolling process. The measurement of the resulting compressive residual stress field was then performed by X-ray diffraction and prompted an experimental crack growth campaign, on small-scale SE(B) and SE(T) specimens, to investigate the behavior of the material at very negative stress ratios. Crack growth tests were then carried out on full-scale specimens and the results successfully compared to those obtained by a simple no interaction predictive model built up considering both the characterized behavior of the material and the measured residual stress field.