A comparative study of the fatigue behavior of two heat-treated nodular cast irons

The mechanical strength of nodular cast iron (NCI) can be improved by heat treatment. Isothermal Ductile Iron (IDI) competes with Austempered Ductile Iron (ADI) for applications subject to dynamic loading. The preliminary metallographic analysis of ADI and IDI showed similar graphite nodule characteristics but different metallic matrix structure. An extensive mechanical characterization of the two materials determined and compared (i) the high cycle fatigue strength, (ii) the fatigue crack growth rates and threshold ΔKth, (iii) the typical crack propagation mechanisms, and (iv) the material heterogeneity in terms of local tensile tests.