The morphology of solidification of thin-section ductile iron castings

The morphology of solidified structures of thin-section ductile iron castings has been investigated by color metallographic techniques. Primary austenitic dendrites were observed to be formed over the whole section of castings when the wall thickness was less than 14mm. The dendrites were thin and long, and the length and the number of dendrites depended on the solidification rate or the wall thickness of the casting. Growth of the dendritic arms was directional, being perpendicular to the surface of castings and along the wall thickness. Interdendrite segregation of Si and Mn is found to occur in thin-section ductile iron castings, as revealed by both color metallography and energy dispersive X-ray microanalysis. The segregation is more pronounced toward the center of castings.