Pearlitic ductile cast iron: damaging micromechanisms at crack tip
Ductile cast irons (DCIs) are characterized by a wide range of mechanical properties, mainly
depending on microstructural factors, as matrix microstructure (characterized by phases volume fraction, grains
size and grain distribution), graphite nodules (characterized by size, shape, density and distribution) and defects
presence (e.g., porosity, inclusions, etc.). Versatility and higher performances at lower cost if compared to steels
with analogous performances are the main DCIs advantages.
In the last years, the role played by graphite nodules was deeply investigated by means of tensile and fatigue
tests, performing scanning electron microscope (SEM) observations of specimens lateral surfaces during the
tests (“in situ” tests) and identifying different damaging micromechanisms.
In this work, a pearlitic DCIs fatigue resistance is investigated considering both fatigue crack propagation (by
means of Compact Type specimens and according to ASTM E399 standard) and overload effects, focusing the
interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules).
On the basis of experimental results, and considering loading conditions and damaging micromechanisms, the
applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in ferritic
DCIs is critically analyzed, mainly focusing the stress intensity factor amplitude role.