Formation and Evolution of Al–Ti Oxide Inclusions during Secondary Steel Refining

The process of Al deoxidation and Ti alloying during RH degassing treatment was studied under an Ar atmosphere at secondary steelmaking temperature (1600—1650°C) in an induction furnace equipped with an oxygen probe and a steel sampler. The formation of inclusions during partial Al deoxidation and Ti addition, and the reduction of Ti–Al–O inclusions by second Al addition are discussed using thermodynamic calculations. Specific attention is given to inclusion size and the compositional relation between the inclusions and the steel. The combination of experimental and calculated results shows that, in order to prevent Ti oxidation in liquid steel, it is essential to control [Al] in liquid steel to a level of approximately 200 ppm prior to Ti addition to achieve around 500 ppm [Ti] with minimal Ti loss during the alloying process.