The non-metallic inclusions which can create surface defects of the cold rolled sheets mainly are the large sized Al2O3 clusters, “Ar+Al2O3” typed inclusions and the entrapped mold powder particles.
Cold Rolled Steel Sheet
Nowadays, under normal and stable casting conditions, the inclusions formed due to the mold powder entrapment can be well controlled.
Among various types of unsteady cast slabs, the quality of the first slab of the cast is deteriorated most severely. In the bottom slab of the cast, inclusions from the mold powder entrapment are much more than the normal cast slabs. Also, the inclusions from mold powders are more in the slabs cast during heat/heat ladle exchange and during SEN quick change than the normal cast slabs.
Cold Rolled Steel for Automotive
It is noted that, the number density of the large inclusions decreases with increasing the casting speed when the casting speed is 1.0-2.0m/min. The harmful inclusions larger than 100μm were found mostly in 0-2mm sub-surface layers of the slabs. To produce surface defects free sheets for automotive, slab surface conditioning treatment should be adopted.
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