Convertor slag properties and their influence upon steel refining

Make the slag and the steel will make itself” is an old phrase in steelmaking. Slags are liquid oxide phases, which play an important role in many pyrometallurgical process. This is also the case in the convertor process.

The convertor process is a necessary step in the steel production. During this process carbon, phosphor and other impurities present in the ‘pig iron’ from the blast furnace are removed and steel is produced. This steel is tapped from the convertor and further refined, next cast, rolled and further finished.

In a convertor, the hot liquid pig iron from the blast furnace is charged together with scrap and oxygen is blown on it. During the process, two main phases are present in the convertor: the liquid metal phase and the slag phase. This slag phase plays an important role in refining the metal phase (removing C, P, Si, etc.) but a good slag will also protect the installation from damage that could be caused by the inherent interactions at high temperatures.

Even though there is general agreement on the importance of the slag and its functions in steelmaking, a profound and complete understanding of slags has not been reached yet. Gaining insight in the process, the working principle and the interaction between the slag and metal phase is rather difficult since a convertor is in reality a ‘black box’. Thermodynamic modelling of the process is a possibility to gain insight and gather more knowledge about the process.

The goal of this PhD is to apply thermodynamic models and calculations upon industrial convertor process, in order to gain fundamental knowledge and understanding of the slag phase

Al2O3-CaO-SiO2 calculated polythermal liquidus projection. The yellow points on the diagram indicate four phase intersection points with liquid Slag. The accompanying temperatures are indicated on the temperature scale.

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