Investigating the Failure Mechanisms of Al2O3-C Refractories Used in Continuous Casting of Steel

Al2O3-C refractories have been widely used in the continuous steel casting process due to their remarkable properties at high temperatures, such as low thermal expansion, thermal conductivity, and high thermal shock resistance. In the present study, the mechanisms and factors of the destruction of Al2O3-C tundish stoppers in the continuous casting process of Khuzestan Steel Company have been investigated. Samples were taken from different stopper sections. In order to study the causes of corrosion and failure, the microstructure and chemical composition of the samples have been examined by scanning electron microscope (SEM), energy dispersive Xray spectrometer (EDS), and X-ray diffractometry (XRD), respectively. The results showed that the destruction of the tundish stopper started with the oxidation of refractory carbon during the pre-heating process. It affects the reduction of corrosion resistance of black refractory due to the two aspects of creating porosity and increasing the wettability of refractory. In addition, refractory decarburization leads to a decrease in the thermal shock resistance of the stopper and will cause a decrease in its useful life of that. After the refractories are exposed to melt and slag, the main stage of corrosion and destruction of the refractories begins. At this stage, the molten steel and slag penetrate the refractory to such an extent that the particles separated from the refractory network merge with the molten steel/slag, and the refractory base is destroyed. Finally, the slag completely covers the refractory, and the alumina particles are dispersed as scattered islands in the ground. Refractory destruction is especially clear in the slag line; As long as the diameter of the stopper in the slag line is reduced (necking), it will not be possible to continue the casting process.