Overload effects on fatigue cracks in a ferritized ductile cast iron

Abstract Ductile cast irons offer an interesting combination of good castability and high mechanical properties, with acceptable costs. This is due to the peculiar graphite nodules shapes obtained not by means of long and expensive heat treatments but by means of the chemical composition control. The relevant mechanical properties of these grades in the as cast conditions can be further modified and improved controlling the matrix microstructure, both modifying the alloys chemical compositions and/or optimizing different heat treatments (e.g., austempering). High temperature heat treatments can imply a modification of the graphite nodules shape due to the carbon atoms solid diffusion process. In this work, the influence of the modification of graphite nodules shape, induced by heat treatment for DCI ferritization, on the damaging mechanisms is investigated, focusing their role on the fatigue crack tips damaging mechanisms after overloadings.