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Mechanism of carbon influence on the chilling tendency and chill of cast iron
from Edward Fras and Marcin Gorny, Cracow, Poland:
The role of various technological parameters on the chilling tendency index, CT and the chill, w of shaped wedge castings made of cast iron can be explained by means of a common analytical model of general validity. Consquently, general relationship (Equation 18) can be found between the CT index and the width of chill, w of cast iron. This theory was experimentally verified using carbon as an example. The graphite nucleation coefficients Ns, b, eutectic cell, growth coefficient, and critical cooling rate, Qcr for the development of cementite eutectic (chill) were determined as a function of the cast iron chemistry. Carbon decreases the nucleation coefficients Ns and b, the temperature range of Tsc and increases the graphite eutectic growth coefficient, and the volume fraction of liquid in the cast iron at the onset of the eutectic solidification, f. In consequence the critical cooling rate, Qcr increases while the chilling tendency index, CT and the width of chill, w decrease. Moreover, it was found that when the carbon content in cast iron increases, the intensivity influence of carbon on the CT index increases through and Ns while it is reduced through Tsc, b and f. In this work, the experimental and theoretical results are found to be in good agreement with each other.