Liquid inclusions are important to avoid nozzle clogging during continuous casting of steel. To minimize clogging tendency at a Brazilian steelworks for a low‐sulphur Ca‐treated peritectic steel, deoxidation technique is changed from only Al addition as deoxidant to Fe–Si ferroalloy followed by Al addition, reducing the amount of Al by 20 wt%. Calcium treatment procedure is not changed. According to steelworks data, clogging occurrences are drastically reduced with this process change. In this context, quenched steel samples are collected from the tundish before and after the aforementioned process change. Nonmetallic inclusions characterization is manually performed using scanning electron microscope. For both conditions—before and after the industrial process changes—the inclusions are typically globular ones. However, before the changes, the inclusion modification is not complete because the core of the inclusions is composed by polygonal spinel. After the changes, the inclusions become homogeneous. Computational thermodynamics is applied to calculate the castability windows; they show that the amount of calcium dissolved in liquid steel is too low before the process changes, and this fact explains the blockage of the tundish nozzles, which is observed at steelworks, due to the deposition of high melting point spinel inclusions.

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