Influence of the solidification microstructure on the mechanical properties of ductile iron

The increase in the nodule count in ductile iron is customarily used as a means to refine the solidification structure. The solidification structure can be better described by the identification of the solidification units. This study investigates the correlation of the nodule count and the cell count. The solidification microstructure has been revealed by color metallography and characterized by the cell count. The results show that both the nodule count and the cell count decrease as the section size increases. Nevertheless, no direct correlation has been found between the refinement of the nodule count and of the solidification structure. The experiments suggest that the nucleation of graphite and austenite are independent. The drop in mechanical properties caused by the increase in section size appears to be related to the presence of unwanted phases at the cell boundaries, and has a weak correlation with the coarsening of the solidification microstructure for castings with "clean" cell boundaries.