<p>Producing high-quality spheroidal graphite irons has become challenging due to the need for high-quality raw materials. The iron-silicon-carbon alloy microstructure is influenced by the non-metallic micro-inclusions (microparticles) dispersed in the melt that can act as exogenous nucleation sites for graphite during solidification. For that, ferrosilicon alloys with specially selected active elements are often added to the melt to modify those micro-inclusions during the production of this material. In this context, the present study investigates the effect of a (Zr, Al, Ca)-ferrosilicon on micro-inclusion dispersion and microstructure of spheroidal graphite irons, as a pre-inoculation addition, where the sulfur and oxygen activity are the highest. The micro-inclusions were analyzed based on their chemical composition, area fraction, number density, and size distribution. The data suggests that the oxide population is greatly affected by coarsening of the oxide inclusions when the melt is pre-inoculated. Furthermore, the pre-inoculation treatment leads to the formation of more complex multiphase inclusions. Graphite nucleus types were statistically reported, and the results show that they are mainly sulfides and nitrides.</p> Graphical abstract <p></p>