Evolution of Calcium Aluminate Inclusions by Cerium Treatment in Al‐Killed Steel during Ruhrstahl–Heraeus Refining Process

The effect of cerium addition during Ruhrstahl–Heraeus (RH) refining process on liquid calcium aluminum inclusion in Al‐killed steel is studied based on plant trials and thermodynamic calculation. Before cerium addition, liquid calcium aluminum inclusion surrounded by an outer CaS layer are observed. Cerium modified liquid calcium aluminum inclusion to CeAlO 3 + CaS + CaO–Al 2 O 3 complex inclusion. The modification process of liquid calcium aluminum inclusion by cerium is different from that of solid Al 2 O 3 or MgO·Al 2 O 3 inclusion and can be concluded as following. Cerium added into molten steel reacts first with liquid calcium aluminum inclusion in molten steel. Then the solid CeAlO 3 and CaO, as reaction product, are surrounded by liquid calcium aluminum. At the same time, CaO reacts with dissolved sulfur, resulting in the generation of CaS inclusions.