Melting of ferrous metals:

In the melting of ferrous metals phosphorus elimination is promoted by slags that are both oxidizing and basic. Sulphur elimination is promoted by slags that are basic and reducing. Therefore melting conditions for optimum sulphur elimination are not the similar as those for optimum phosphorus elimination. For instance melting of steel in the fundamental open-hearth furnace occurs under oxidizing conditions. The fundamental open hearth decrease phosphorus contents of steel to extremely low values but is less capable in regard to sulphur. In the basic cupola melting of cast iron occur under dropping up conditions. Sulphur is readily eliminated but under ordinary melting practices little decreased of phosphorus occurs. In electric furnace melting of steel phosphorus and sulphur both might be reduced to extremely low values by a double slag melting practice. The metal is melted under a greatly oxidizing basic slag to accomplish phosphorus elimination; this slag is then eliminated and replaced along a basic reducing slag to lower the sulphur content.