Distribution of non-metallic inclusions in IF steel slab

In order to explore the distribution of inclusions in the thick direction of the IF steel slab, scanning detection was conducted on the section of the slab using SEM. It was found that inclusions in the slab were mainly TiN, Al₂O₃ and Al-Ti-O inclusions, and TiN and Al-Ti-O inclusions were mainly near the surface. From the surface to the center of the slab, the average size of TiN and Al-Ti inclusions was gradually decreased. The distribution of Al₂O₃ inclusions was relatively uniform, whlie inclusions larger than 5 μm or 10 μm mainly distributed on the fixed side of the slab. The evolution behavior of inclusions during solidification and cooling processes was calculated by thermodynamics, and it was found that in the molten steel were Al₂O₃, while inclusions eventually changed to TiN and Al₂O₃ due to the precipitation of TiN during solidification and cooling processes. Based on the calculation of the precipitation temperature and the solidification rate of TiN, it can be found that with the increased of T.N content from 15 ppm to 35 ppm, the precipitation temperature of TiN increased from 1 515 ℃ to 1 535 ℃, and the critical precipitation solidification rate decreases from 0.89 to 0.79.