Cs. Narendranath et Mn. Srinivasan, EFFECT OF COOLING RATE VARIABLES ON THE SOLIDIFICATION TIME AND MICROSTRUCTURE OF PERMANENT-MOLD MAGNESIUM-TREATED IRON CASTINGS, Journal of testing and evaluation, 23(4), 1995, pp. 281-287
This paper deals with studies on the effect of cooling rate variations
on the solidification times and microstructure of permanent mold magn
esium-treated cast iron. Cooling rate variations were brought about by
changes in the casting size or mold preheating temperature or mold wa
il thickness. The results of this investigation indicate that the soli
dification time of magnesium-treated iron casting is always greater th
an that of an untreated iron casting, when the cooling rate variables
are similar. Since the morphology of graphite in the two cases is diff
erent, it is thus indicated that graphite morphology affects the solid
ification time. Though the solidification time of magnesium-treated ir
on permanent mold castings shows an increase when the casting size is
increased, no unilateral increase or decrease is observed when the mag
nitudes of the other two variables, viz., mold wall thickness and mold
preheating temperature favor decrease and increase in cooling rate re
spectively. Microstructural analysis indicated that random variations
in the graphite morphology, despite the residual magnesium being above
the required limit, were primarily responsible for the random variati
ons in solidification times. The reason for this randomness has been d
iscussed in terms of heat transfer. Further experiments were conducted
where the heat transfer variables were chosen based on this analysis
and it was possible to achieve proper trends in the solidification tim
e. The graphite shape of the castings in these experiments had good no
dularity, with the size being related to the cooling rate.