Prediction of the fatigue limit defining mechanism of nodular cast iron based on statistical microstructural features

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The microstructure and nodule count of large-size nodular cast iron components vary spatially. These variables are qualitatively known to affect the fatigue limit, yet no model exists to quantify the effects. Some of the physical aspects, such as the clustering of graphite nodules and the role of ferrite microhardness in ferritic–pearlitic nodular cast iron fatigue, have been unclear in the literature. This paper aims to clarify and quantify these aspects. In the absence of casting defects, the largest ferrite with a crack initiating graphite is shown to be the physical, and statistical, explanation for the mixed grade fatigue limit.