Improving High-Temperature Performance of High Si-Alloyed Ductile Iron by Altering Additions

High alloyed Si ferritic ductile irons can offer potential benefits because they combine high strength, ductility at room temperature, and low oxidation rate at high temperature. However, there is one known drawback and that is these cast irons have limited performance during thermal cycling due to a significant drop of ductility at warm temperatures. This decrease in ductility has been linked to poisoning ferrite grain boundaries by Mg. Therefore, thermodynamic simulations were used to identify altering additions which were able to meditate this negative effect by forming intermetallic phases with Mg. To verify thermodynamic predictions, three alloys were cast including a base and two high Si ductile irons with additions of P and Sb. High-temperature performance of these alloys was experimentally verified including tensile properties at warm temperatures (350–550 °C), oxidation in air at temperatures (700–800 °C), and thermal cycling between 300 and 800 °C. SEM and TEM analyses confirmed that the studied additions reacted with Mg forming different compounds which could prevent poisoning ferrite grain boundaries and improve high-temperature performance of high Si ductile iron.