The processes of formation and melt-down of the softening-melting zone are discussed based on the results of dissection of water-quenched blast furnaces.
1) Iron ore granules of the ore layer change to half-molten state through softening. The transformation of the granules is mainly effected by the hot reducing gas passing through the ore layer.
2) Two processes of melt-down of metal are considered as followed: One is the formation of “Icicle”from the mixture of metal particle and molten slag. The other is the rapid carbonization in metal which contacts with hot coke at about 1500 C. Reduction of silicon in metal does not occur in these processes.
3) The original slags generating in granules of pellet and lumpy ore are rich in FeO. After separating from the granules they are blended with the slag from sinter. FeO in total slag is further decreased by gas-reduction. Consequently, FeO content of the slag just before melt-down is only a few percent.
4) The drop metal and slag have changed their composition after the blowing down of the furnace. Therefore, the change in composition during the dropping process is much difficult to be estimated.