Distribution Characteristics of Inclusions in the Surface Layer of Interstitial Free (IF) Steel Slab

The surface quality of interstitial free (IF) steel is determined by inclusion distribution in the slab. It is necessary to determine the optimal cleaning depth of the slab in different states when the surface of IF steel slab is cleaned automatically by on-line flame. Based on the equipment and production practice in ANSTEEL, slab samples have been taken from the inner and outer arc surfaces of each slab along the width direction to study the shape, quantity and maximum size of inclusions under different cleaning depths. The results indicate that with the increase of cleaning depth, the number of inclusions with size of 20-50 mu m decreases in the second slab of the sequence. The number of inclusions with size > 50 mu m increases slightly. The number of inclusions with size > 20 mu m in the steady and transition slab decreases slightly. When the slab is not cleaned, the maximum size of inclusions in these three slabs is 500 mu m, 200 mu m and 200 mu m, respectively. As the critical size of inclusions is 100 mu m for the occurrence of the surface defects, the cleaning depth in the second slab should be 4-5 mm, and the cleaning depth of the steady slab and the transition slab should be 2 mm.