Abstract
In order to clarify the mechanism of blowhole formation, an experimental study has been made of unidirectional solidification of iron for carbon contents of the melt of 0.01 to 0.40% at a solidification rate of about 5mm/min. Critical composition for blowhole formation has been determined. Above 0.15% carbon the critical oxygen concentration is almost constant (0.0025%), while it increases with decreasing carbon content below 0.15%. A macroblowhole originates from a small blowhole formed in the interdendritic area. A model based on the equilibrium solidification suggests that the small blowhole is formed without supersaturation of carbon and oxygen in the interdendritic liquid. The growth of blowholes which proceeds at oxygen contents below the critical concentration is accounted for by the model of steady growth of cyclindrical blowholes.
