On the Prediction of Residual Magnesium and Nodularity in Ductile Iron by Thermal Analysis

Morphology of graphite affects the mechanical and physical properties of cast irons. It is known that the spheroidal shape of graphite promotes both tensile strength and ductility. The morphology of graphite is generally quantified by the percent nodularity and/or graphite shape factors (e.g. roundness, sphericity, compactness, aspect ratio). From the quality control aspect, the nodularity is controlled by the residual magnesium content determined by the Optical Emission Spectrometry (OES). However, the nodularity is also affected by the cooling rate and the sulfur level. Therefore, the percent nodularity alone cannot be precisely predicted by the residual magnesium. In this study, the Thermal Analysis (TA) was used to predict the residual magnesium and the nodularity of ductile iron. The newly created TA demonstrated the reliable prediction as the effect of the residual magnesium, sulfur level and the cooling rate were combined in forms of cooling curves. The correlations of the residual magnesium, the Maximum Cooling Rate (MCR) and the angle of the cooling rate curve (θ) at the end of solidification were shown in this work. Finally, the relationships were used to encode in the software for the on-site prediction.