Microstructure Change and Primary Slag Melting of Sinter in the Cohesive Zone of a Blast Furnace

To clarify the primary slag melting behavior of sinters, the microstructure and phase changes during the melt producing process were observed: Sinters were heated under the temperature history and the CO/CO2 ratio simulating a blast furnace condition and quenched from several different temperatures between 1 000 and 1 250 degrees C. The microstructures of the quenched samples were observed by electron probe micro-analyzer. The olivine-like melts have been locally observed as primary melts above 1 100 degrees C, the compositions of which have higher FeO content and lower CaO/SiO2 ratio with an increase in the heating temperature. On the other hand, microstructures composed of round shape wustite and 2CaO center dot SiO2 have been observed on a sample quenched from 1 250 degrees C. In that local area, the olivine-like melts cannot be found. This may imply that although the olivine-like melts originally existed between wustite and 2CaO center dot SiO2, the melts have been completely dissolved into 2CaO SiO2 owing to the large solubility of olivine in 2CaO center dot SiO2, resulting in the resolidification of the melts. The eutectic structure composed of wustite, 2CaO center dot SiO2 and 2CaO center dot Al2O3 center dot SiO2 have also been observed on a sample quenched from 1 250 degrees C.