Mechanisms of strength decrease in the initial reduction of iron ore oxide pellets

As an important material for ironmaking, oxide pellet may break and disintegrate due to the strength decrease during reduction, which will cause significantly adverse impacts on field production. Strength decrease in the initial reduction of oxide pellet was researched in this paper. Results indicate that the strength of pellets drops sharply from 2973.3 N/pellet to 742.0 N/pellet (strength loss reaches 75.04%) when reduced for 1 min. Microstructure investigation of the pellets reveals that the increase of porosity and generation of particles defect in periphery lead to the strength loss. And those inducements gradually shift to the inner part of pellets with the reduction proceeds. In addition, the effects of iron oxide phase transition on strength change were studied. The largest strength loss (about 75.85%) occurs as hematite is reduced to magnetite. Then with magnetite reduced to wustite, strength continues to decrease slightly. Finally strength improves with the formation of metallic iron phase.