The Effect of Inclusions on Through-thickness Directional Fatigue Behavior of S355N Steel Plate

Microalloyed S355N steel plates are extensively used in bridge and high-rise building structures. One of the factors affecting the mechanical properties is the size and morphology of inclusions. In this research, microalloyed S355N steel plates with different sizes of inclusions were examined. One contained long manganese sulfide inclusions (LI material) and the other had short ones (SI material). Fatigue and tensile tests were carried out in through-thickness direction of both materials. Additionally, the fatigue test results were verified by “statistics of extreme value” (SEV) method. The tensile and fatigue tests revealed that toughness and fatigue limit of LI material were 65% and 30% less than those of SI, respectively. The SEV analysis conservatively predicted the fatigue limit of SI material. However, it was not accurate enough in the case of LI. These results could be explained using the behavior of manganese sulfide inclusions as short fatigue cracks in steels.