The morphology and chemistry evolution of inclusions in Fe-Si-Al-O melts

This study aims to elucidate the process of inclusion precipitation in Fe-Si and Fe-Si-Al melts. Deoxidation experiments were carried out in a vacuum induction furnace (VIF) at 1873 K (1600 °C). In the Si-deoxidation experiments, spherical SiO₂ of 1∼2 μm diameter was dominant. When 3 wt pct Si and 300 ppm Al were added, such that Al₂O ₃ and mullite were thermodynamically stable, the resulting inclusions depended on the addition sequence. When aluminum was added before silicon, spherical aluminum oxides were dominant after the Al addition, but after the Si addition, the number and size of alumina decreased and Al-Si oxides and mullite appeared with increasing time. When silicon was added before aluminum, spherical SiO₂ was dominant after the Si addition, but after the Al addition, spherical and polygonal alumina inclusions were dominant. When Al/Si was added simultaneously, polygonal alumina inclusions were dominant initially, but with time, Al-Si oxide and mullite inclusions increased in numbers. If the Al amount in the Al/Si addition was increased to 600 ppm, only alumina was found. This study shows how, under similar thermodynamic conditions, the transient evolution of inclusions in iron melts in the Si-Al-O system differ depending on the alloy addition sequence.