Laboratory tests on the reduction degradation behavior of sinter were carried out to clarify the influence of each factor, which includes reduction degradation index (RDI), reducibility index (RI), and temperature profile. Furthermore, the materials were extracted from the shaft of the working blast furnace to ascertain the validity of the tests results. Based on these information, the sinter degradation model was formulated to describe the sinter breakdown. The findings obtained are as follows ;
1) Sinter breakdown occurs significantly in the temperature range of 600 to 800°C. This range coincides with that of hematite being reduced.
2) Maximum amount of fines degraded during reduction depends on RDI, RI and temperature profile, under which reduction reaction occurs.
3) Increase of RDI leads to the deteriorating gas permeability originated by the increasing amount of fines and it exerts adverse effects on the gas flow distribution in the radial direction of the blast furnace.