The interaction between non-metallic inclusions and surface roughness in fatigue failure and their influence on fatigue strength

In this study, the influence of non-metallic inclusions on the fatigue behavior of 30MnVS6 steel containing different inclusion sizes and surface roughness has been investigated. Scanning electron microscope (SEM) was used to examine fatigue fracture origins. It was concluded that the non-metallic inclusions were dominant fatigue crack initiation sites in both smooth and rough specimens. This was justified by the calculation of stress intensity factor generated by both surface roughness and non-metallic inclusions, based on Murakami’s model. In addition, it was found that for a given stress, the critical inclusion size could be increased by eliminating the surface roughness.

► The fatigue strength of a tested steel was affected by inclusions and surface notches.
► Inclusions were the main fatigue crack sources even in rough specimens.
► The stress intensity factor represented the behavior of inclusions properly.
► In rough steels the effect of inclusions was intensified by surface roughness.
► The critical inclusion size increased when surface roughness was removed.