Evaluation of near surface defects and fatigue properties of cast iron

This research work aimed to find out means to ensure fatigue strength of cast components. Componenta carries out R&D to avoid casting defects which have detrimental effect on the fatigue properties. Extensive metallographic studies and fatigue experiments were herein performed to support this development work. Clear differences in the amount of degenerated graphite and defects near the casting surface were seen in the micrographs at different surface positions. An ultrasound scanning microscope was used to evaluate applicability of Rayleigh wave velocity measurements to detect and classify small surface defects. This technology was investigated as a candidate method for non-destructive quality control. Some fatigue crack initiation sites could be correlated with the detected surface defects, but the influence of defects on the fatigue properties could not be evaluated. The fatigue strengths of the studied variants were within a common scatter band. But the results of ultrasonic measurements are in perfect agreement with the microstructural measurements. They are also fully in line with the trends in fatigue lives and scatters.