Conditions of deposition of alumina and metal on ZrO2-CaO-C refractory has been investigated in comparison of Al2O3-C refractory by laboratory scale test. The results are summarized as follows.
(1) When high aluminum and alumina inclusions were contained in the molten steel, ZrO2-CaO-C refractory was easier to be deposited than Al2O3-C one.
(2) The deposition may be composed of two steps.
The first is the formation of fine oxide layer (the network alumina) in the hot face during very short time after immersion.
The second is the deposition of non-metallic inclusions on the fine oxide layer.
(3) The generation of the fine oxide layer is due to the following reactions. Direct reaction of aluminum in the molten steel with silica and zirconia contained in the refractory. Suboxide gases (SiO, ZrO) reduced by graphite in the refractory react with aluminum in the molten steel.
