Formation Mechanism of Silica Inclusion during Solidification of Fe-Si-O Alloys

Abstract

During the repeated cooling and heating of Fe-Si-O alloys (0.07<Si%<0.81) from 1600°C to 1555°C, specimens were sampled from the melt at 1555°C by using Cu sampler, silica tube (inner diameter : 4mm) or silica sampler (10mm). The behavior of the oxide phases formed during solidification of the specimen was reported, with particular attention paid to the distribution and morphology of dendritic inclusion precipitated in the intercellular region of solidified structure. From a qualitative investigation of formation mechanism, it was concluded that very fine silica particles, presumably of several tens angstrom in size, were readily formed in the boundary layer enriched with silicon and oxygen, and the reaction Si+2O = SiO₂ proceeded there to equilibrium during solidification, and they were pushed along by the advancing solid and gradually accumulated just ahead of the solid-liquid interface. Silica inclusion was formed by successive adhesion of silica particles to the possible nuclei suspended in the liquid phase after enough accumulation was built up, and the morphology of silica inclusion was strongly influenced by the size of very fine silica particle.