Interaction between steel and distinct gunning materials in the Tundish

The interaction between refractory gunning material and liquid steel in the tundish gives rise to inclusions in the steel, therefore influencing the steel cleanliness and causing nozzle clogging during continuous casting. This interaction was investigated through laboratory experiments under controlled atmosphere at 1550°C, in which steel was equilibrated for certain times in shaped crucibles made of gunning mass. Steel was sampled repeatedly during the tests and the crucibles were quenched after interaction. A FeO layer with a thickness of 5~30 µm was observed at the steel/gunning material interface during the interaction tests. In the steel samples, two types of inclusions were found: (I) Al2O3 and/or AlTiOx inclusions, the number of which decreases with holding time; (II) numerous small Fe-Mn-O-S inclusions, the size of which increases with time. The former inclusions are relatively larger than the latter ones, and are believed to be originally present in the steel, while the latter inclusions are generated during the interaction tests (reoxidation of the steel) or during the solidification of the samples (secondary inclusions). On the other hand, large inclusions originating from the gunning material (Al2O3 and MgO with impurities), were observed to be located in the steel close to the steel/gunning material interface. The composition and microstructure of the gunning materials affect the inclusion population in the steel. The steel reoxidation rates as traced by the Fe-Mn-S-O inclusions appears to increase with higher SiO2 and FeO content in the original gunning materials.