【Abstract】 Study was carried out on the microstructure of the three types of slag at high temperature in BOF by means of a hot stage microscope. The results are listed as follows. The phase components in all slag are C 2S、C 3S、(Mg Fe)O as well as C 2F. Under fusibility temperature the three types of slag were heterogeneous phase in which C 3S and RO phase coexisted as solid and C 2S microcrystals separated from liquid at quickly cooling rate, under over heat temperature the slag containing high FeO x low basicity and MgO were homogeneous phasc. But the slag containing high FeO x , high basicity and MgO still was heterogeneous phase. The CaO FeO SiO 2 and C 2S C 3S C 2F ternary diagrams showed that at high temperature C 2S was dissolved into liquid by FeO and C 2F. But C 3S was difficult to dissolve. The slag only with a small amount C 3S and non saturated MgO was homogeneous.更多还原