Model representations of ingots produced by various casting processes are invariably based on the assumption of process stability. Models of grain growth in, for example, the remelting processes depict stable progressive columnar-dendritic grain growth as solidification progresses, transforming to an equiaxial grain structure at the appropriate point. However, industrial casting processes are very often carried out under less-than-ideal conditions where the procedure involves inadvertent instabilities such as interruptions in metal flow or abrupt changes in the process heat balance and so do not follow the stability assumptions contained in the models. In such instances, the properties of the product depend more on the results of the instability than on the assumed stable conditions. In this work we demonstrate the effects of typical examples of such instability. It is suggested that a major direction in modelling development should be towards an understanding of the extent to which instability can be tolerated relative to the product requirements. Such an understanding would greatly assist in the establishment of suitable quality standards governing the production of high-quality alloy castings.

Moderated by: Mark Schneider / Jakob Olofsson