Mechanism of Deposition of Inclusion and Metal in ZrO₂-CaO-C Immersion Nozzle of Continuous Casting

Abstract

The conditions of deposition of alumina and metal on ZrO₂-CaO-C refractory have been investigated in comparison with Al₂O₃-C refractory by laboratory scale test. The results are summarized as follows:
(1) When aluminum content is low, or amount of alumina inclusions are little, ZCG refractory is more hardly to be deposited than AG, as is reported before. On the contrary, ZrO₂-CaO-C refractory was more easily deposited than AG in the case of some level of aluminum content and non-metallic inclusions.
(2) The deposition may be composed of two steps. The first is the formation of a fine oxide layer (the network alumina) in the hot face during the very short time after immersion. The second is the deposition of non-metallic inclusions on the fine oxide layer.
(3) The generation mechanism of the fine oxide layer is due to the reaction between aluminum in the molten steel and the next substances.
(1): SiO₂ in the refractory,
(2): SiO cand CO gases generated by the reaction between SiO₂ and graphite in the refractory,
(3): ZrO₂ in the refractory.
Concerning to ZrO and CO gases generated by the reaction between ZrO₂ and graphite in the refractory, more detail study is necessary to clarify the contribution to the reaction.