Thermal analysis of compacted graphite cast irons containing various levels of Mg and S

Abstract

Thermal analysis was carried out during solidification of cast irons containing various levels of magnesium (0.006%-0.036%) and high initial levels of sulfur (0.023%-0.031%). The cast irons studied had a near-eutectic composition, and were treated with a Fe-Si-Mg alloy. Seven heats were performed and for each of them four samples of liquid metal were taken for chemical and thermal analysis. The non inoculated samples showed microstructures containing either flake or compacted graphite (with nodularity values below 53%). The graphite shape was related, by a statistical approach, to the parameters of the cooling curves. Simple thermal analysis was unable to differentiate between irons with “good” compacted graphite with nodularity below 20% and those with nodularity values between 20 and 53%. The correlations between the parameters resulting from derivative thermal analysis and nodularity of CG irons were obtained, but the error due to data scattering could not be neglected. The uncertainty observed in the correlations may be overcome if the strategy for CG iron production is based on a treatment target window where only the undertreated melts would be corrected.