De-Slagging

De-Slagging

De-slagging operations are carried out to remove impurities from the furnace. During melting and refining operations, some of the undesirable materials within the bath are oxidized and enter the slag phase.

It is advantageous to remove as much phosphorus into the slag as early in the heat as possible (i.e. while the bath temperature is still low). The furnace is tilted backwards and slag is poured out of the furnace through the slag door. Removal of the slag eliminates the possibility of phosphorus reversion.

During slag foaming operations, carbon may be injected into the slag where it will reduce FeO to metallic iron and in the process produce carbon monoxide which helps foam the slag. If the high phosphorus slag has not been removed prior to this operation, phosphorus reversion will occur. During slag foaming, slag may overflow the sill level in the EAF and flow out of the slag door.

The following table shows the typical constituents of an EAF slag :

Component	Source	Composition Range
CaO	Charged	40 - 60 %
SiO2	Oxidation product	5 - 15 %
FeO	Oxidation product	10 - 30 %
MgO	Charged as dolomite	3 - 8 %
CaF2	Charged - slag fluidizer
MnO	Oxidation product	2 - 5%
S	Absorbed from steel
P	Oxidation product