Microstructural Observation of Dendrite and Its Surrounding Regions Formed during Solidification of Gray Cast Iron

Abstract

Molten metal for hypoeutectic gray cast irons was poured into a top-open-type sand mold with furan resin. Unsolidified molten metal was discharged from the mold before the molten metal completely solidified. This resulted in the formation of artificial defects on the solid–liquid phase boundary. Dendrites and other microstructures were observed to be formed near the artificial defects. Sharp dendrite stalks with periodic protrusions around the periphery were observed in macroscopic images. This observation confirmed that the dendrites were growing toward the center of the hole formed by the discharge of the unsolidified molten metal. These results corresponded to the observations made using a scanning electron microscope. Graphite flakes formed parallel to the dendrite branches were observed on the cross-sectional microstructures near the solid–liquid phase boundary. Scanning electron microscopy showed that perlite colonies segmented the dendrite stalk. The area around the dendrite, namely the region formed by eutectic solidification, was composed of perlite, ferrite, and graphite flakes.

 

This Paper was Originally Published in Japanese in J. JFS 92 (2020) 333–338.