High-silicon and molybdenum (SiMo) ductile iron is a common heat-resistant alloy that may be exposed to high-temperature wear during service in many of its applications. The wear behavior of four SiMo ductile iron alloys was evaluated at different temperatures up to 750 °C. This research focuses on the influence of various Mo contents on the microstructure, structural stability, and hence, the wear performance of such alloys. Thermodynamic calculations proposed the phase diagrams, critical transformation temperatures, and phase volume fractions in all samples by means of Thermo-Calc software. The dilatometry measurements were carried for confirming the theoretical results of Thermo-Calc thermodynamic calculations. The results revealed that the microstructure of SiMo ductile cast iron consists of nodular graphite and a ferrite matrix with carbides embedded in the fine precipitates at the grain boundary regions. The type of carbides and the nature of these fine precipitates are discussed according to EDX and SEM results. Adding molybdenum enhanced the wear performance of SiMo by decreasing the weight loss by about 40–70% compared to a Mo-free alloy. This is due to the increased molybdenum carbides, which increase hardness and improve wear resistance in SiMo alloys. The high temperatures have a negative effect on reducing the wear resistance at 250 °C. On the other hand, the wear resistance unexpectedly started to increase at higher temperatures of 500 °C and 750 °C because of the contribution of oxidative wear with abrasive wear by forming a protective oxide layer. Furthermore, the obtained results supported the idea that adding molybdenum improves wear resistance at high temperatures. Hence, SiMo has the potential to be wear-resistant material in wider applications requiring high-temperature wear resistance.

Standard SiMo ductile cast iron automotive alloys are typically subjected to various hostile environmental conditions. For the current investigation, SiMo with a silicon content of 5% and molybdenum contents ranging from 0 to 1.5% was used. In two corrosive environments of 0.6 M NaCl and 0.5 M H2SO4, the study intends to present the corrosion behavior of high silicon molybdenum ductile cast iron (SiMo). Moreover, the impact of changing Mo on the microstructural characteristics has been investigated. The SEM-EDX examinations revealed that the nodule counts, M6C carbides, and lamellar pearlite increased while the ferritic matrix decreased with increasing Mo contents. It is clear that the addition of Mo reduces cast iron's rate of corrosion and thus increases its corrosion resistance. The results showed that SiMo cast iron alloy with 1.0 wt% Mo had a lower corrosion current (Icorr) in 0.6 M NaCl solution while lower corrosion current (Icorr) with the cast iron containing 1.5 wt% Mo in 0.5 M H2SO4 solution, which resulted in the lowest corrosion rate. The occurrence of a galvanic couple between the alloy matrix and the graphite nodules results in electrochemical corrosion, with the largest corrosion rates taking place at Mo-free alloy in both media.