Ferrosilicon (FeSi) is an alloy of iron and silicon with a very variable silicon content between 10 % and 90 %. It is used as a socalled master alloy in steel production, which is added in small amounts in order to adjust the properties of the melt, the cooling process and the finished product. The main advantage of FeSi is its deoxidizing effect (i. e. it reduces metals from their oxides), but it also helps to prevent the loss of carbon.