Article ID: ISIJINT-2024-356
It has been reported that an increasing H2 gas ratio of the reducing gas in the blast furnace promotes the low temperature reduction disintegration of the iron ore pellet. Reduction of the pellet sample proceeds uniformly under higher H2 condition at 500°C. Microcracks with the size of several micrometer form at the primary particles of iron oxide and it promote fine particles formation after the drum test. Macrocracks with the size of several millimeter form inside of the pellet after reduction and it promotes the volumetric destruction. In this study, the temperature dependence of reduction disintegration of self-fluxing pellet under higher H2 condition was examined.
Pellet sample was reduced under CO and CO-H2 gas conditions at 600°C and 700°C. After reduction, the disintegration test was conducted using the drum. Under higher H2 condition at 600°C, the density of microcracks decreases with increasing reduction degree and it leads to lower of the RDI value than that at 500°C. The reason is that the volumetric expansion by the reduction from hematite to magnetite at 600°C is not significant compared with that at 500°C. The difference of reduction degree at the center and near the surface of the pellet increases with increasing the reduction temperature. Reduction reaction proceeds more topochemically by increasing reduction temperature and the addition of hydrogen. This change leads the macrocrack formation, which is same mechanism under CO gas condition at 500°C. At 700°C, on the other hand, this microcrack was not observed because the volumetric expansion by the reduction is lower than that at lower temperature. Therefore, the effect of hydrogen addition on disintegration is not significant at 700°C.
