Because the behaviours of MgO and Al2O3 during slag formation of high basicity sinter are not clearly understood, the effects of MgO and Al2O3 on softening-melting properties are always arguable. In this paper, four kinds of sinter containing different MgO and Al2O3 content are investigated. Some observations are obtained. The mechanism of the influence of MgO and Al2O3 on softening properties of sinter are different. Al2O3 has priority over MgO to enter into slag phase and forms low-melting point phase while MgO remains unslagged state and mainly exists in wustite as FeO–MgO solid solution. When sinter melts, the viscosity of the slag generated from sinter containing high MgO and Al2O3 content is low, which could result in low pressure drop. As MgO and Al2O3 content increase, the main minerals of residual slag change from 2CaO•SiO2 to merwinte and melilite. The changes of the minerals in slag phase can well explain the trend of softening-melting characteristic temperatures.
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