<div class="htmlview paragraph">The fatigue behavior of five microalloyed steels, processed with hardnesses between 25-28 HRC containing microstructures ranging from precipitation-hardened ferrite-pearlite to bainite, were evaluated in both low cycle (strain controlled) and high cycle (stress controlled fatigue. The vanadium-bearing steels included, 15R30V, 1522 MoVTi, 1522 MoVTiS, 1534 MoVTi, and 1534 MoVTiSi. Conventional quench and tempered 4140 steel was used as a reference.</div> <div class="htmlview paragraph">Low cycle fatigue (LCF) data for all steels were similar. Subtle microstructural-dependent differences in the high-strain amplitude region of the LCF curves were attributed to the effects of retained austenite, present in some of the non-traditional bainitic steels. In high cycle fatigue, all steels exhibited similar properties, except for the ferrite-pearlite steel (15R30V) which exhibited the lowest endurance limit, an observation which was attributed to crack nucleation in coarse-grained ferrite.</div>