Charakterisierung des Clogging-Layer-Aufbaus im Eintauchausguss mit unterschiedlichen Tracer-Elementen

During the production of steel, the individual process steps create non-metallic inclusions (NMI) that cause build up in the submerged entry nozzle (SEN) in the final production step. This clogging process leads to a loss of quality and reduced production numbers, which requires a detailed investigation. In the present work, the clogging problem is investigated using three oxide tracers (barium -, strontium - and gallium oxide). The aim is to distinguish the adherent layers using the NMI doped with tracers and to investigate the exact reasons for the adhesion.
For validation, four industrial tests were carried out on an industrial scale. To build different clogging layers in the SEN, the doping always takes place in the same way. For this purpose, the first batch is doped with the tracer element barium, the second with strontium and, in one case, the third batch with gallium oxide. The aim of this doping was to clearly differentiate the respective adhesion layers in the SEN. The tracer was added during the taping of the BOF to ensure optimal mixing and incorporation into the inclusions. While barium and strontium tracers were added in the form of carbonates, gallium was added directly as an oxide. During production, samples were taken at different points to be able to map the tracer levels over time. After the end of production, the SEN was analyzed in the scanning electron microscope (SEM).
Despite careful examination of the SEN, no tracer oxides could be detected in the clogging layers using SEM. Apparent barium and strontium levels were incorrectly displayed due to overlay effects in the SEM (barium with titanium, strontium with silicon). This means that it is not possible to examine the clogging layer with these three used tracers. Compared to a reference sample, analysis of the particles reveals a decrease in the average size of inclusions due to the addition of tracers. The analysis showed that the average size of the NMI could be reduced to ≤ 2 µm by adding tracer.