Studying On Cleanliness Changing Regularity Of Ultra-low Carbon Steel Unsteady Slab

During the unsteady casting process, the serious slag entrapment and reoxidation lead tothe casting slab cleanliness deteriorating. So, the slabs produced in the unsteady casting process,always are downgraded or as steel scrap. This treatment method results in the slab yielddecreasing and the production cost increasing. This paper focuses on the cleanliness of theultra-low carbon steel slab produced in the beginning and finishing casting stage, and comparedwith the normal slabs. The results are as follows.(1) With the first slab length increasing, the inclusions quantity, the T[O] and the nitrogencontent all displayed a decreasing tendency. And the first slab cleanliness is closed to thosenormal slabs at the length of3.5m. So the cut length of first slab is at least3.5m. The maininclusions of the first slab are TiN, Al2O3, TiN-Al2O3, SiO2, Al2O3-SiO2, TiO2-Al2O3-SiO2, andAl2O3-SiO2-MgO, and small sum of the composite inclusions containing Ca.(2) The inclusions quantity, the T[O] and the nitrogen content of final slab all decreasealong casting direction. The inclusions quantity in the final slab, which is more than thedistance of1.5m from the end, is consistent with the normal slabs. But the T[O] and thenitrogen content are more than the distance of1m from the end. So the cut length of final slab is1.0m. It is found the main inclusions are TiN, Al2O3, TiN-Al2O3, SiO2, Al2O3-SiO2,TiN-Al2O3-SiO2, and a little bar-shaped composite inclusions.(3) Through comparing the cleanliness of the slab in different stages of casting,it is foundthat mould slag entrapment happens during the stage of the beginning and the finishing ofcasting, the beginning stage and the finishing of casting both happen reoxidation, and thebeginning stage of casting is more serious.