Nowadays, magnesia carbon refractories are used in steel making units. However, the partial replacement of the primary raw materials in magnesia carbon production by recycled ones gains importance due to resources and energy savings and reduced gas emission. Nevertheless, refractory materials in direct contact with liquid steel are a potential source for non-metallic inclusions. On the other hand, refractory materials have the potential to influence present inclusions arose from the steel making process itself. Regardless of their origin, non-metallic inclusions have detrimental impact on mechanical properties of metallic components dependent on their morphology and chemistry. Thus, in-depth knowledge regarding the interactions of refractory lining materials with the steel melt and in particular the population of non-metallic inclusions is indispensable.
Therefore, this work conducts immersion tests in a steel casting simulator with industrially fabricated MgO-C refractory materials differing in the MgO grade of the used raw materials. Moreover, immersion tests with refractories based on MgO-C recyclates were conducted. The immersed specimens were characterized by means of optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffraction. The immersed specimens were covered by newly formed structures mainly consisting of MgO and magnesium-aluminate spinel. Moreover, corrosion products of the quaternary system of Al₂O₃-MgO-CaO-SiO₂ were detected with higher proportion for the lower MgO grade specimens.
The solidified steel blocks after the immersion tests were investigated regarding their population of non-metallic inclusions using automated feature analysis and general guidelines for the investigation of non-metallic inclusions in metal matrix were highlighted. It was shown that the grade of the immersed refractory material had an impact on the population of non-metallic inclusions in terms of inclusion chemistry and morphology. Moreover, no negative impact of the usage of magnesia carbon refractories containing recyclates on the inclusion population was observed.