Inclusions in IF steel continuous casting slab and hot rolled sheet

Inclusions are important factors affecting the surface quality of IF steel. This paper studied the IF steel slab and hot-rolled plate produced by a domestic factory. The two-dimensional morphology, size, quantity, distribution and composition of inclusions were analyzed by optical microscope, scanning electron microscope and energy spectrum. The results show that the rolling action of hot rolling process makes the inclusion gathered at 1/4 of the width of continuous casting billet migrate to the edge. This results in the highest inclusion index at the edge of the hot rolled plate, indicating that the inclusion accumulation zone is hereditary during the rolling process. Compared with the constant casting billet, the inclusion percentage under 20 meters in the hot-rolled plate increases slightly, while the inclusion percentage above 50 meters decreases slightly. During the hot rolling process, the inclusion of large alumina particles in the continuous casting slab is extruded and deformed into long strip in the hot rolling plate, which is easy to form surface strip defects. The inclusion aggregation was found at 30 mm from the inner arc side of the casting billet, and the inclusion index was highest at 0.5 mm from the inner arc side of the hot rolled plate. The difference in equivalent strain caused the inclusion aggregation to migrate to the surface. There are mainly four kinds of microscopic inclusions in IF steel continuous casting slab and hot rolled plate, which are Al₂O₃, TiN, Al₂O₃-TiO_x and SiO₂ composite inclusions respectively, and there is little difference in the percentage of each kind of inclusions between them.