Fundamental mechanism of effects of MgO on sinter strength

Abstract

MgO-containing flux may have a series of effects on the quality of sinter and performances of the blast furnace. Thus, the fundamental mechanism of the effects of MgO on the sinter strength was investigated. Both the chemical reagent and industrial flux were used for preparing the specimens. The experimental results show that the sinter strength decreases with MgO addition. There are three reasons for it. The first reason is diffusion rate. Almost all of the CaO may react with Fe₂O₃ and generate CaO·Fe₂O₃, but most of MgO cannot react with Fe₂O₃, and it still remains in the state of original minerals. The diffusion rate of MgO in iron oxide is only 17.51 μm/min in 30 min. The second reason is the fluidity and ability to generate liquid phase. In the case of Fe₂O₃ mixed with CaO, there is some liquid phase formed above 1200 °C, while in the case of Fe₂O₃ mixed with MgO, even at 1200 and 1220 °C, there is still no liquid phase. The third reason is self-strength. In the case of industrial flux, the compression strength of the specimens made of Fe₂O₃ and limestone is 0.52 and 0.71 kN at 1150 and 1180 °C, respectively, while that of the specimens made of Fe₂O₃ and magnesite is 0.48 and 0.56 kN, respectively. Therefore, the fundamental mechanism of the effects of MgO additive on sinter strength can be better understood based on the diffusion rate of MgO in iron oxides, the fluidity of liquid phase, and the self-strength of bonding phase.