Abstract
Irons containing various amount of C and Si were melted in a high frequency induction furnace with a 12kW, 3,000Hz motor generator unit. The melt was superheated to 1,530 deg C for nodularization treatment in a crucible using 1.6wt% of Fe-Si-Mg alloy. After the nodularizing reaction subsided, the melt was post-inoculated with Fe-Si and was poured in CO2 process sand mold with section sizes of 3mm, 6mm and 9mm. The presence of carbides and nodule count were determined with an image analyzing computer. The nodule count depended strongly on carbon equivalent and the relationship was expressed in a linear equation. For each cooling rate of specimen there was a characteristic nodule count (the critical nodule count) above which free carbide did not appear. The relationship between the critical nodule count and the cooling rate was expressed in the following quadratic equation ; N=0.58R2+19.07R+1.01, where N is the nodule count and R is the cooling rate.
