Steel and slag combined in HT-CSLM: A new approach for the in-situ investigation of non-metallic inclusions

The High-Temperature Confocal Scanning Laser Microscope (HT-CSLM) is an effective tool for in-situ investigations of surface phenomena of various materials and has proven its suitability for metallurgical processes. It is widely used to observe phase transformations, melting behavior, agglomeration of non-metallic inclusions (NMIs), or dissolution of particles in slags. However, these processes have been studied as stand-alone experiments until now. In this work the authors describe the development of a set-up for the combined investigation of steel, slag, and NMIs in-situ in the HT-CSLM to observe agglomeration, movement towards the slag, detachment, and dissolution of NMIs in a single experiment. The developed procedure takes geometrical, chemical, and physical aspects into account and includes safeguards to prevent leaking of liquid steel or slag into the furnace chamber by using a dual crucible approach. As the slag (partially) covers the steel, it must be transparent, leading to limitations in the composition of both steel and slag. This work focuses on different steel/slag combinations of medium-carbon steels with varying alloying elements and deoxidation concepts. The slags used are low melting CaO-Al2O3-SiO2 slags. For some experiments, alkali oxides were added to the slags to lower their melting points as well as their viscosities.