Xue Qingguo

Influence of reduction degree on the burden microstructure during the softening and melting process

For pellet, sinter, and a mixture of both, microstructure evolution of different burdens during the softening and melting process were investigated by softening experiment of single particle load. The results showed that the reduction degree have an ifluence on the softening and melting behavior. In the case of a low reduction degree, a slag phase substrate and a myrmekitic iron structure were formed on the periphery area of the molten burden. While the substrate of slag phase and the islands of wustite structure were formed in the center area. In the case of a high reduction degree, there were a slag phase substrate and myrmekitic iron texture both the peripheral and central areas. The slag-iron distribution had a structure in which the slag phase was cut in the metal iron phase. 2FeO·SiO2 content as a low melting point phase in the slag decreased sharply, and this resulted in the increase of the slag-iron separation temperature. The variation of the Ca/Si ratio in the interface between the pellet and the sinter indicated that enhancement of the reduction degree caused the increase of initial temperature and the decrease of interaction distance.

Kinetics Calculation of the Non-isothermal Reduction of Pellet

Abstract The reduction tests of pellet were carried out from room temperature to 1,373 K in the condition of traditional blast furnace (TBF) and oxygen blast furnace (OBF) by thermogravimeter measurement. The apparent activation energy E, pre-exponential factor A and the controlling steps of reaction were determined by the non-isothermal method of Coats–Redfern. In the condition of TBF, the reduction is controlled by solid diffusion to interfacial chemical reaction at initial stage, and gas diffusion at final stage. In the condition of OBF, the controlling step switched from solid diffusion to gas diffusion + interfacial chemical reaction in the beginning and the interfacial chemical reaction at the late stage. Meanwhile, the transition temperature points of the controlling step were predicted. The transition temperatures are 750℃ and 900℃ in TBF and 630℃ (earlier 120℃ than in TBF) and 900℃ (after the insulation) in OBF.