The influence of oxides and sulfides in gray cast iron on the growth morphologies of MnS and on the nucleation of graphite was experimentally investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX) analysis with evidences that shows the possible nucleation sites for graphite nucleation. Thermodynamic studies have been done on the influence of varying sulfur concentrations on the nucleation of MnS in the melt and during solidification. The consumption of dissolved oxygen and sulfur in the melt during the cooling process was analyzed and we explored how this influenced the nucleation process of oxides and sulfides. A sequential nucleation concept of oxides and MnS is proposed in relation to the growth morphology of MnS and graphite with respect to the mechanical properties of cast iron. The nucleation of new oxides and sulfides was analyzed using thermodynamics and compared to our experimental results. Graphite nucleation on substrates other than MnS, such as MoS2 oxides and (Mo,Cr)S, was experimentally analyzed along with the influence of the substrates on graphite nucleation and growth morphology.
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