One of the functions of secondary refining in steelmaking is to remove non-metallic inclusions produced through deoxidation of the steel bath during the process. Removal of these inclusions occurs in three fundamental stages: flotation, separation and dissolution of the inclusions in supernatant slag. Given that dissolution is subject to the action of slag, this study aims to clarify the inclusion absorption capacity of industrial slags and factors that influence slag properties in absorbing inclusions, as well as the impact of each factor on the cleanliness of the steels analyzed. To that end, the results of industrial steel and slag samples collected during the different stages of secondary refining were analyzed. The amount and chemical composition of the inclusions was determined by SEM/EDS (scanning electron microscopy coupled with energy-dispersive spectroscopy). The chemical composition of slag samples was measured by XRF (X-ray fluorescence) and subsequently submitted to thermodynamic simulations using FactSage 6.4 software. Calculations were made with the SlagViscosityPredictor, which uses FactSage 6.2 software. This made it possible to establish the chemical composition and proportion of the solid phase in the slags and inclusions, as well as the effective viscosity of the slags. The efficiency of absorption inclusion by the industrial slags was found to be greater in the presence of high thermodynamic driving force between slags and inclusions, low slag effective viscosity and when inclusions were not liquid.

In the production of special steels, inclusions have a significant influence on final product quality. Moreover, there is a growing need for constant improvement of mechanical and machinability properties, such as in the production of complex pieces for the automotive applications. The main objective of this study was to conduct a thermodynamic study aimed at preventing clogging problems during continuous casting (CC) and the formation of undesirable inclusions. Alumina (Al2O3), spinels, and calcium sulfide (CaS) are potential sources of defects during rolling and steel forging. The specific goals of this study were: (1) To determine the phases and compounds formed in the inclusions as a function of composition and casting temperature adopted for high sulfur Al‐killed Ca‐treated steel, and (2) To establish chemical composition conditions resulting in the formation of less harmful inclusions for steel castability. Based on the literature and previous studies by the authors, calculations were carried out using FactSage commercial software and related databases. The calculations were performed using the steel temperature and chemical composition in the CC tundish. The results of these calculations were used to estimate the composition of steel and non‐metallic inclusions (oxides and sulfides) at the given steel temperature. Based on these calculations, it was predicted a calcium content range where inclusions contained a high proportion of liquid phase (i.e., “liquid window”). The results of thermodynamic simulation were compared to industrial outcomes in terms of inclusion composition and casting index. The thermodynamic predictions were validated and confirmed by industrial results.

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