Monotonic and fatigue test results on three nodular irons with different mean nodule sizes are reported. Scanning electron microscope studies of the fracture surfaces indicate that the controlling fatigue cracks initiate from the most severe flaw such as microshrinkage cavities, slag inclusions or porosity. The effect of precycling on fatigue life is explored. Predictive techniques sometimes used for estimating the fatigue resistance of wrought metals are shown to be unsatisfactory for this nodular iron.
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