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

摘要

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 (degrees 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 CEL) from hypoeutectic to eutectic composition is obtained as follows: CEL = [%C] + 0.23 [%Si] - 0.03 [%Mn] + 0.32 [%P] + 0.64 [%S] + 0.02 [%Ni] + 0.06 [%Cr]. This CEL is different from the commonly used CE since it is determined from liquidus. We investigated how the difference of carbon equivalent (CE/CEL) application in the range of hypoeutectic to eutectic composition affected on the cast iron and revealed that CEL = [%C] + 0.23 [%Si] should be applicable.