Fatigue and fracture resistance of ferritic ductile cast iron: the effect of Sb and solidification time

In this paper, we explore the effect of inoculants and solidification time on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI). For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on three different material conditions. They are produced under fast cooling (solidification time 2h45min), representative of thin walled castings, and very slow cooling (solidification time 10-13h), representative of thick walled castings, this latter with and without the addition of Sb. It has been found that the long solidification time leads to an overgrowth and degeneration of the spheroidal graphite nodules. The addition of Sb avoids the formation of chunky graphite observed in the slowly cooled condition but results in large exploded graphite nodules. These effects impact negatively on tensile strength, total elongation and fatigue strength. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of the fast cooled condition. Metallurgical and fractographic analyses are carried out to explain this behaviour.