Investigation of the Difference Between Carbon Equivalent from Carbon Saturation Degree and that from Liquidus

Carbon equivalent of cast iron is known as the following equation: CE = [%C] + (1/3) [%Si]. This equation is basically calculated from the carbon solubility in hypereutectic composition. On the other hand, liquidus from hypoeutectic to eutectic composition in Fe–C phase diagram is well known. Liquidus temperature (hereinafter referred to as T L ) can be measured easily with thermal analysis by focusing primary crystallization temperature. In this study, the effects of elements on T L and carbon equivalent in cast iron were examined from the view point of cooling curve, carbon flotation, and internal shrinkage, and a more accurate equation for calculating carbon equivalent is suggested. It is revealed by the experiment that the relationship between T L and elements from hypoeutectic to eutectic composition is as follows; T L (°C) = 1625 − 110 [%C] − 25 [%Si] + 3 [%Mn] − 35 [%P] − 71 [%S] − 2 [%Ni] − 7 [%Cr]. Dividing this equation by carbon coefficient, the carbon equivalent equation of liquidus (hereinafter referred to as CE L ) from hypoeutectic to eutectic composition is obtained as follows: CE L = [%C] + 0.23 [%Si] − 0.03 [%Mn] + 0.32 [%P] + 0.64 [%S] + 0.02 [%Ni] + 0.06 [%Cr]. This CE L is different from the commonly used CE since it is determined from liquidus. We investigated how the difference of carbon equivalent (CE/CE L ) application in the range of hypoeutectic to eutectic composition affected on the cast iron and revealed that CE L = [%C] + 0.23 [%Si] should be applicable.