Experimental evaluation and modeling of sulfur content and anisotropy of sulfide inclusions on fatigue behavior of steels

This paper presents and discusses experimental results on the effect of sulfur content and sulfide inclusions on fatigue behavior of steels with different sulfur and hardness levels under different loading directions. Ductility and toughness of the transverse samples were found to reduce considerably by the increase in sulfur content, while the differences in the yield and ultimate tensile strengths were not significant. High sulfur resulted in significant adverse effect of inclusions on fatigue behavior of the transverse samples, particularly in the long life regime. The difference between the high and low sulfur materials was larger at the higher hardness level. Both sub-surface and surface failure modes were observed at long lives, where the sub-surface failures exhibited much longer life. The √area parameter was used to estimate the fatigue limit of the materials used, resulting in reasonable estimations in most cases. Roessle–Fatemi equation, which is used to predict the strain-life curve of steels based on hardness, was modified in order to incorporate the effects of sulfur under transverse loading. It is shown that this modified equation results in relatively good predictions of fatigue lives.