Non-Metallic Inclusion Distribution in Surface Layer of IF Steel Slabs

Non-metallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis (OPA) method. It was found that most non-metallic inclusions larger than 10 μm existed in the subsurface layers of 0.5 — 3.5 mm from the slab surfaces and very few large non-metallic inclusions were found in the inner regions (≥4.5 mm from slab surfaces). In addition, it was found that at high casting speed level (1.4 m/min), even a slight change of casting speed could result in a remarkable increase of the non-metallic inclusions. Thus, at high casting speed, changing the casting speed should be avoided or considerably lower speed changing rate must be used.