Undercooling, cooling curves and nodule count for near-eutectic thin-walled ductile iron castings

Abstract

A solidification model for ductile iron, including Weibull formula for nodule count, has been presented. The principal assumptions of the kinetic nature of growth, depending on undercooling in respect of the eutectic equilibrium temperature and austenite liquidus line, have been adopted, disregarding the diffusion processes, which was justified by the rapid course of the crystallization process in a thin-walled casting. From this model, the following parameters can be determined: cooling curves, kinetics of austenite and eutectic nucleation, austenite and eutectic growth velocity, and volume fraction. The correctness of the mathematical model has been experimentally verified by comparison with literature data in the range of the most significant factors, which include temperature field, the value of maximum undercooling, the value of minimum and maximum temperature on a cooling curve, maximum undercooling, the recalescence and graphite nodule count interrelated with the casting cross-section. © 2014 ISIJ.