Corrosion Behavior of SiMo Ductile Cast Iron in Different Corrosive Environments

Abstract

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.