The Individual Influences of B and Cu on Graphite and Inclusion Populations in Spheroidal Graphite Iron

The individual influences of copper (Cu) and boron (B) on the populations of graphite and inclusions in spheroidal graphite iron (SGI) were investigated. An automated scanning electron microscope procedure was used to map the number of particles, their chemistry, and their Feret diameter and area. It was observed that the number density of graphite nodules increased with increasing concentration of B up to 25 ppm, after which it remained stable with further increase in B-content. The nodule number density increased as the content of Cu increased. Inclusions with an apparent eutectic structure rich in Mg and Cu were observed in regions that likely are the last liquid to freeze. B was not observed to significantly affect the populations of sulfides, oxides, nitrides, or carbides, with respect to number density, shape, and size. A good correlation was found between experimental observations and thermodynamical simulations regarding the effect of B on nonmetallic inclusions. The thermodynamical simulations predicted formation of the intermetallic phases $${{\text{Mg}}_{2}{\text{Cu}}}$$ and $${{\text{MgCu}}_{2}}$$ , which could not be confirmed experimentally. The chemistry and structure of the Cu–Mg inclusions therefore remains unclarified.