The Anisotropic Fatigue Behavior of Forged Steel

A study was conducted to investigated two different types of anisotropic fatigue behavior of forged steel. The second type of anisotropic fatigue behavior was observed in forged or rolled hardened steels, in which the UTS > 1000MPa. This behavior was attributed to the existence of elongated manganese sulfide (MnS) inclusions, oriented parallel to the rolling or forging direction. It was observed that the resulting oriented microstructure led to a continuous decrease in the fatigue limit with increasing fibering orientation angle and showed a minimum at 90° when the inclusions were perpendicular to the stress axis. It was also observed that the fatigue behavior was more pronounced in a standard sulfur steel (50CD4 QS) with a dense MnS population as compared in a low sulfur steel (50CD4 LS). This implied that the anisotropy level depended on the volume and distribution of inclusion and the mechanical properties of the material matrix.