Abstract
Ultrasonic fatigue tests were carried out on two automotive steels: AISI/SAE 4140T and 1045, to investigate the fatigue endurance of these materials and the mechanisms of crack initiation and propagation under this modality of loading. Tests were obtained at room temperature and without control of environmental humidity; the last parameter was maintained between 50 and 65%.Ultrasonic fatigue results show that the effect of non-metallic inclusions plays an important role in the decay of fatigue endurance for the 4140T steel, together with the effect of previous heat treatments. Concerning1045 steel, non-metallic inclusions play an important role too, but this time the temperature and variation of ductility with temperature induce an effect on the ultrasonic fatigue endurance. Finally, the fracture surfaces were analyzed in order to obtain the principal trends of crack initiation and propagation on these steels, under the ultrasonic loading modality.
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