Effect of Si content and Sn addition on solidification behavior and graphite morphology of compacted graphite iron

Compacted graphite iron is mostly produced by simultaneous treatment with spheroidizing elements (Mg, Ce) and anti-spheroidizing elements (Al, Ti and Sn). Because the CGI is the most sensitive type of cast iron to the thickness variation, higher cooling rates lead to increase in the amount of nodular graphite in the microstructure. Therefore, the most important difficulty in casting such alloys is obtaining high percentage of compacted graphite in sections where cooling rate is high. The aim of this study was to investigate the role of silicon and tin on solidification behavior and graphite morphology at different cooling rates. Different values of silicon and tin contents in base metal were cast in step blocks with different cooling rates by in-mould process. The results showed that at lower cooling rates (1.35 and 1.85 ), the percentage of compacted graphite and graphite aspect ratio were decreased by increasing of silicon content. Increment of the amount of carbon equivalent which promotes the nodular graphite nucleation is the main reason of this phenomenon. In addition, increasing of nodular graphite percentage at higher cooling rates (3.9 and 8.9 ), decreases the amount of compacted graphite and graphite aspect ratio. Moreover, at the cooling rate of 18.3 , which is the critical cooling rate for cast irons, increasing of Si content up to 3.6% did not change the morphology of graphite phase but increased the tailed spheroidal graphite and reduced the formation of carbide. The results also showed that raising tin content from 0.03% to 0.15%, increases percentage of compacted graphite and graphite aspect ratio at lower cooling rates (1.35 and 1.85 ) , but higher cooling rate reduces this effect of tin in increasing of compacted graphite iron.