Casting powder is composed of CaO, SiO2, Al2O3, Na2O/K2O and C free. This powder is mainly used in slab, billet and bloom casting. The low melting constituents in the powder quickly create liquid slag, that enters into the gap between the mold and the solidifying shell of the billet. A very small amount of casting powder is used, but continuously and over the casting duration. The casting powder melting can be witnessed in slowly in layers. Which is why the liquid metal's top surface in billet / slab / bloom remains safeguarded from the atmosphere. It is a good option to consider if you want to improve the quality of metal surface.