Evolution Mechanism of Nonmetallic Inclusions in Fe‐1.5Al‐xSi (x = 0.5–3.0 wt%) Alloyed Steels

The effects of Si content of steel melts containing 1.5% Al as well as alloying sequence of Si and Al on the evolution of inclusions are investigated. The SiO2 inclusion is primarily formed when Si (=0.5–3.0 wt%) is added to the melts at 1873 K, and the area fraction (AF) of the inclusions decreases over time. The subsequent addition of 1.5% Al to the Si‐alloyed steel (i.e., 3.0Si→1.5Al) increases the AF of inclusions due to the formation of Al2O3. The population density function (PDF) analysis for the preferential Si alloying shows a fractal distribution, indicating that the inclusions grow by a collision mechanism. PDF analysis shows a lognormal distribution because Al2O3 inclusion is formed and grows after subsequent Al alloying. Alternatively, when 1.5% Al is preferentially added to steel, Al2O3 clusters are formed. The AF of Al2O3 cluster decreases over time. When 3.0% Si is subsequently added to the Al‐alloyed steel (i.e., 1.5Al→3.0Si), singular Al2O3 particles are mainly observed. Because the Al alloying results in the formation of Al2O3 regardless of the alloying sequence and Si content, it is important to float up and separate Al2O3 cluster to improve the cleanliness of high‐Si‐Al‐alloyed steels such as electrical steels.