Influence of non-metallic inclusions on the fatigue properties of heavily cold drawn steel wires

The influence of non-metallic inclusions on the fatigue properties of heavily cold drawn steel wires is studied. Through a fractography study it is possible to link the inclusion properties, such as chemical composition, geometry, size and location, to the fatigue properties.Comparing the Stress Intensity Factors (SIF) of non-metallic inclusions to the threshold value for long crack growth shows that the defect size that should be used to calculate the SIF is larger than the inclusion size itself. This is validated using Scanning Electron Microscopy (SEM) in combination with a Focused Ion Beam (FIB). This SEM/FIB study shows that the region around non-metallic inclusions is characterized by alterations in the microstructure that should be taken into account. It is calculated that the SIF increases with 16.5±3.6% compared to Murakami’s way of calculating SIF of non-metallic inclusions.