Investigating of the effect of hardness, size and position of inclusions on the fatigue strength of the steel AISI 304

One of the most crucial factors influencing the strength and quality of steels is the presence of non-metallic inclusions. Studies demonstrated that non-metallic inclusions in industrial parts diminish their fatigue strength. On the other hand, their hardness is another influential parameter affecting the fatigue strength of steels. Therefore, this research investigated the impact of non-metallic inclusions on the fatigue strength of AISI 304 steel with three hardness of 170, 250, and 330 Vickers. This research revealed that as the hardness decreases, the fatigue strength of the part also decreases. Additionally, an examination of the failure surfaces of the parts using scanning electron microscopy (SEM) indicates that non-metallic inclusions are the root cause of fatigue failure in the samples. Finally, employing Murakami relations, parameters such as stress intensity factor and critical inclusion size were determined for steel with hardness levels of 170, 250, and 330 Vickers. The critical inclusion size for steel with hardness levels of 170, 250, and 330 Vickers was calculated as 32.7, 24.8, and 15 micrometers, respectively.