Discussion on Usability of the Niyama Criterion for Porosity Predicting in Cast Iron Castings

The paper refers to previous publications of the author, focused on criteria of casting feeding, including the thermal criterion proposed by Niyama. On the basis of this criterion, present in the post-processing of practically all the simulation codes, danger of casting compactness (in the sense of soundness) in form of a microporosity, caused by the shrinkage phenomena, is predicted. The vast majority of publications in this field concerns shrinkage and feeding phenomena in the cast steel castings – these are the alloys, in which parallel expansion phenomenon does not occur as in the cast irons (graphite crystallization). The paper, basing on the simulation-experimental studies, presents problems of usability of a classic, definition-based approach to the Niyama criterion for the cast iron castings, especially of greater massiveness, for prediction of presence of zones of dispersed porosity, with relation to predictions of the shrinkage type defects. The graphite expansion and its influence on shrinkage compensation during solidification of eutectic is also discussed.