Abstract
	Feroalloys producing in OFZ a.s. Instebne, plant Široka, has successful tradition of feroalloys producing. In this time, OFZ a.s. is producing FeMnC and FeSiMn. Author deal with properties evaluation and with  FeMnC slag efect on FeSiMn producing. FeMnC slag contains large mangannese content. It is very difficult to know its behavior in melting proccess next to the FeMnC in electic arc furnace. This slag is using as charging material to the FeSiMn producing. It is very  difficult to know the form and phase of manganesse fixing  in FeMnC slag.  Because of  technology problems we can coordinate the chemical composition by raw materials  and taping proces in electric arc furnace, but we can not find out running of producing. It is possible by only predicting on the bazic of chemical composition of raw materials and metal, or on the value of viscosity of liquid FeMnC slag. Author deal with utilization of FeMnC slag as raw material for FeSiMn producing a its effect on taping proces. It is very difficult, that silicates and aluminate of mangane dont exist. Manganesse form and phase in FeMnC slag has effect on reduction Mn from slag, teping temperature and on the all productivity FeSiMn. Here is very different to analyze lokal chemical analyze.