Graphite nucleant (microinclusion) characterization in Ca/Sr inoculated grey irons

Complex (Mn, X)S compounds nucleated on Al2O3-based sites were found as the major nucleation sites for graphite flakes in both un- inoculated and inoculated grey irons. (Mn, X)S particles (1–8 fun) and their corresponding nuclei (0.1–2.7 μm) were characterized as size, morphological features and distribution patterns of different elements (Mn, S, Ca, Sr, Al, O, Fe), under the influence of inoculant type (HP-FeSi, Sr-FeSi, Ca-FeSi) and cooling rate (4.3 and 542°C/sec). These particles present so common features for all irons (distinct core; always Al and O presence in the core; Mn and S throughout the compound; usually high number, etc), but also the peculiar features (Ca presence throughout almost all compounds independent of inoculant type; Sr mainly in the core of Sr-FeSi treated iron; ovoid tendency of compounds in Ca-FeSi treated irons; lower nuclei size, lower Mn/S ratio in the compounds body and more complex (Mn,X)S compounds in inoculated irons, etc). More intricacy of (Mn, X)S compounds in inoculated irons leads to lower crystallographic misfit given the graphite (more favorable to graphite nucleation).