Thermochemical Evaluation of Cast Iron Slags Generated from a Holding Furnace

In the production of cast iron, slag is a reaction product from the process steps such as melting, spheroidization and inoculation elements combined with oxygen and sulfur. The slag is a mixture of oxides and sulfides that often appears on the surface of the molten iron, where it can be removed or, in the worst case, carried into the mold during casting causing slag defects. It is accepted that slag is a part of the cast iron process by most foundries, and it is given little attention as long as it is manageable. However, some slag compositions have a more negative effect on the production and are less appreciated by the foundry operators than others. In this context, two different slag samples from an 80-ton holding furnace were collected to study their compositions and give a plausible explanation for their different behavior. They were referred to as Good and Bad slag samples by the operators. The Bad slag also caused more slag defects in the castings. The slags were evaluated by X-ray fluorescence spectroscopy and combustion techniques to measure the total concentrations of oxygen and sulfur. This information was used as input parameters for thermodynamics calculations, using the CALPHAD method, to evaluate the equilibrium phases of the slag samples and their behavior as a function of temperature. The results show that the Good slag has a higher solid content than the Bad slag. This might be associated with an easier removal from the molten iron by the operators than a more liquid content slag. Furthermore, there may be less slag entering the mold with higher solids, and thus, the Good slag has fewer casting defects.

Automated summary

This study investigates two different slag samples and their behavior in cast iron production. The results show that the slag with higher solid content is easier to remove from the molten iron, leading to fewer casting defects.