Removal of Alumina Inclusions from Molten Steel by Ceramic Foam Filtration

The efficiency of removal of solid alumina inclusions by filtration and the distribution of inclusions captured through the thickness of the filter was investigated for an aluminum killed 316 stainless steel casting. A mold design was developed using modeling software to produce two castings that fill simultaneously, one with a filter and the other without a filter. The design was optimized to produce the filtered casting and unfiltered casting from a single ladle pour, while also matching the fill rates and avoiding turbulence and reoxidation during pouring. Samples from the filters and the castings were analyzed using an SEM with EDS and automated feature analysis to measure the efficiency of inclusion removal for a 10 ppi zirconia foam filter. Results showed that inclusion removal efficiency depends strongly on the initial inclusion concentration and that the alumina inclusions are captured within the filter at the filter web-steel interface. This study also documented that inclusion floatation inside the mold cavity plays a role in reducing the inclusion concentration in the casting. The distribution of alumina inclusions captured through the filter thickness was quantified using elemental mapping and the inclusion distribution was found to decrease exponentially, following first-order capture kinetics.