Graphite nodules and fatigue crack propagation micromechanisms in a ferritic ductile cast iron

Since 1948, ductile cast irons (DCIs) are able to combine the toughness of steels with the good castability of grey irons. They are widely used in a number of applications, for example wheels, gears, and crankshafts in cars and trucks. Their fatigue crack propagation resistance depends on loading conditions, chemical composition, matrix microstructure and graphite elements morphology (graphite volume fraction, graphite elements nodularity, graphite elements distribution and dimensions). In this work, a ferritic DCI was investigated focusing fatigue crack propagation micromechanisms: step by step fatigue crack propagation tests were performed considering compact-type specimens, and crack propagation micromechanisms were investigated by means of scanning electronmicroscope and digitalmicroscope lateral surfaces observations, considering different loading conditions. Furthermore, overloads were also considered during fatigue crack propagation, investigating their influence on DCI fatigue crack propagation micromechanisms.