Abstract
A second phase was introduced around graphite nodules in ferritic spheroidal graphite cast iron and graphite steel by induction quenching and tempering at 200°C or 550°C to improve their fatigue characteristics. Completely reversed bending fatigue tests were carried out. The treated irons have the endurance limit superior to that of spheroidal graphite cast irons having ferritic, bull's eye and pearlitic structures. The endurance limit of the treated cast irons and graphite steels rises by increasing the volume fraction of the second phase, but that of the graphite-tempered sorbite steel (1.2%C: with nodular graphite like malleable cast iron) having the second phase volume fraction 40% or more is lower than that of the 10% material. Such an improvement in fatigue characteristics is attributed to the fact that the harder phase introduced around the graphite nodules prevents initiation of fatigue crack at the graphite-matrix interface.
