Abstract: This paper shows how MeltLab measures the smoothness of the curve to determine the degree of nodularity of a final ductile iron sample. Taking the casual observance of Dr. Lampic, we have turned up a surprisingly reliable way to measure the growth shape of graphite by the bursts of energy produced by the growth on vermicular graphite. This method is ideally suited to MeltLab’s strong points of precision, noise suppression, and derivative calculation.

The natural shrinkage that occurs during the solidification of Ductile Iron can be offset by the expansion caused by the formation of graphite. Though this has been known for some time, thermal analysis has some interesting contributions to understanding exactly what is going on, and offers some opportunities for better control of late graphite expansion in moderate section sizes. Different modes of solidification are examined and measured, and the early and late graphite content are calculated using thermal analysis. Carbon flotation is seen as a fourth form of solidification that is both hypereutectic and hypoeutectic. Shrinkage is seen as a lack of late graphite growth needed to offset the natural contraction of the Ferrite. Grain boundary shrinkage can be seen as an escape mechanism for minor unfulfilled contraction. Stress relief heat treat increases the graphite volume thereby collapsing any remaining of the grain boundary shrinkage and improving fatigue life and other physical properties.

Thermal analysis is a fast and inexpensive way to see if a furnace of metal meets the basic criteria for pouring. Often melting is the bottleneck of a foundry and having a furnace of iron or aluminum or copper alloy on hold for the laboratory results can be costly. Some foundries have great success with thermal analysis results while others have problems with inaccuracy. This paper tries to cover all the sources of inconsistency and how to correct them so that foundries can get the most good out of these instruments.

Note: this is only a working paper and references have been left out.

One promising new technology is the rapid classification of microstructure by thermo analysis. Current technology consists of either pouring a sample with two ears on it for micro analysis or creating a micro lug in the runner system of a mold and digging the lug out for grinding and polishing. Both techniques are "after the fact" or as we often say, "post mortem" since a bad result results in scrapping already poured castings.