Formation of CO Macroblowholes during Solidification of Iron-Carbon Alloy Ingot

Abstract

Formation of CO macroblowholes during solidification of Fe-C alloys containing 0.03-0.3% C cast into a mold has been investigated. Critical composition for blowhole formation was determined from examining four types of formation of macroblowholes. Critical oxygen concentration decreases with increasing carbon content from 0.05% to 0.15%, while it is constant above 0.15% carbon. Below 0.05% carbon, the critical oxygen concentration tends to be almost constant. Microporosities formed in the interdendritic region grow to macroblowholes. The number of microporosities increases with increasing oxygen content. The mechanism of macroblowhole formation is explained. The critical composition for blowhole formation of 0.1% carbon is calculated theoretically using a model on the basis of experimental data of solidification rate and primary dendrite arm spacing. Good agreement is found between calculation and experiment for the critical composition.