Graphite Formation in Cast Iron

In the first phase of the project it was proven that by changing the ratio between the thermal gradient and the growth rate for commercial cast iron samples solidifying in a Bridgman type furnace, it is possible to produce all types of graphite structures, from flake to spheroidal, and all types of matrices, from ferritic to white at a certain given level of cerium. KC-135 flight experiments have shown that in a low-gravity environment, no flotation occurs even in spheroidal graphite cast irons with carbon equivalent as high as 5%, while extensive graphite flotation occurred in both flake and spheroidal graphite cast irons, in high carbon samples solidified in a high gravity environment. This opens the way for production of iron-carbon composite materials, with high carbon content (e.g. 10%) in a low gravity environment.

By using KC-135 flights the influence of some basic elements on the solidification of cast iron will be studied. Ground experiments have shown that no clear planar interface occurs in aluminum rich Fe-e samples. This is probably due to convection of aluminum which has a low density as compared with the base metal. This hypothesis will be checked by low gravity experiments.

The mechanism of flake to spheroidal graphite transition will be studied, by using quenching experiments at both low and one gravity for different G/R ratios. By this procedure flake graphite eutectic-liquid, compacted graphite eutectic-liquid and spheroidal graphite eutectic liquid interfaces will be frozen, and cerium segregation at the graphite frozen liquid interface will be determined by means of Auger microscopy. In this way, a monolayer absorption of cerium would be possible to document. It is expected to produce a theory on the eutectic solidification of cast iron, documented by direct experiments, which will explain the formation of various types of graphite, from flake to spheroidal.