Influence of surface defects on the fatigue crack initiation in pearlitic steel

Tensile fatigue tests were performed under load control, with constant stress range Δσ on pearlitic steel wires, from the hot rolled bar to the commercial prestressing steel wire (which has undergone seven cold drawing steps). Results show that fatigue cracks in pearlitic steels initiate at the wire surface starting from small defects, whose size decreases with the drawing process. Fatigue cracks created from defects (initiation phase) exhibit a fractographic appearance consisting of ductile microtearing events which can be classified as tearing topography surface or TTS, and exhibit a remarkably lower spacing in the prestressing steel wire than in the hot rolled bar. In addition, some S-N tests were performed in both material forms under a stress range of about half the yield strength. In these tests, the main part of the fatigue life corresponds to the propagation stage in the hot rolled bar whereas such a main part of the life is associated with the initiation stage in the case of the prestressing steel wire