**5. Conclusions**

This chapter highlights the impact of nonmetallic inclusions on the quality and performance of a cast product and how this can ultimately cause premature component failure. The practical application of root cause analysis methods in resolving failure problems is discussed using a failed automotive brake rotor as a case study. The investigation concluded that the automotive brake rotor failed prematurely due to the influence of nonmetallic inclusions in the swan neck of the rotor. The inclusions were concentrated at approximately 1.620 ± 0.237 mm away from the disc's inner radial perimeter, reducing the design thickness of the rotor's swan neck. A cluster of inclusions in the rotor's neck region provided stress concentration and crack initiation sites. Multiple microcracks were initiated within and around the oxide inclusions and propagated through the interface between the flaky graphite and the pearlitic matrix. Examination of the rotor's hardness, chemical composition and microstructure suggested that the failed disc had been produced from the appropriate gray cast iron material and met the specification requirements; and that there were no deficiencies or abnormalities found with the disc material. The evaluation revealed that nonmetallic inclusions were the primary cause of the failure, and preventive recommendations were provided to forestall future recurrence and ensure high-quality castings.
