Influence of artificial defects on fatigue strength of EA4T axle steel repaired by 316L extreme high-speed laser cladding

This study systematically evaluates the damage tolerance of EA4T railway axle steel repaired by extreme high-speed laser-clad 316 L. The effects of electro-discharge machining (EDM) notches and impact-induced defects on fatigue behavior were compared. Tension-compression fatigue tests show that fatigue strength decreases with defect size for both types of notches. However, impact-damaged specimens exhibit higher fatigue strength than EDM-notched specimens at identical sizes. Microstructural analysis attributes the poor performance of EDM-notched specimens to multi-crack initiation in the brittle recast layer, while impact-notched specimens primarily undergo single-crack initiation. Modeling results indicate that EDM defects align well with El-Haddad predictions, whereas impact defects exceed these predictions due to beneficial plastic deformation and compressive residual stresses. At low impact velocities (<200 m/s), stress concentration at the repair interface has negligible influence on fatigue strength. At higher velocities, however, the combined effects of residual tensile stresses at notch edges and cyclic loading lead to final failure by overload. Subsequent fatigue cracks initiate from these fractures, reducing overall strength. Compared with the EA4T base material (234 HV 0.1 ), the EHLA-316 L coating (227 HV 0.1 ) shows superior impact resistance. This advantage is attributed to its higher work-hardening capacity (n = 0.41 vs. 0.19) and longer phase of uniform plastic deformation. Nevertheless, the lower fatigue crack growth threshold of 316 L limits its damage tolerance when pre-existing defects are present. These findings elucidate the fatigue behavior of EHLA-316 L repaired specimens under various damage conditions and provide crucial guidance for optimizing material selection in axle rehabilitation.