Manganese distribution and effect on graphite shape in advanced cast irons

The manganese contribution to a change of the graphite shape (in nodular graphite cast irons) has never been revealed. We made obvious the negative action of this element on the nodularization of graphite. Using SEM, we observe a significant change of the shape of the precipitated graphite (decrease of the shape coefficient values), depending on the cooling rate, the nature and the quantity of the nodularizing elements. The distribution of manganese and silicon in the metallic matrix and in the nodular graphite of cast irons with various amounts of manganese was studied using Castaing Scanning X-ray Microprobe. The distribution profiles of (KαMn and KαSi) show that polycarbides appear on the graphite periphery in the cast iron with manganese contents over 1.0% (confirmed by SEM-EDX analysis). These chemical compounds influence the slowing down of the expected growth of graphite during the austenitic decomposition. This allows us to suggest that manganese would be added to the referenced antinodularizing elements group (O, S, halogens and Pb, Te, Ti, Cu, Al, Sn, Sb, Bi).