The key to the development of material-specific simulation models was the specific feeding behavior of cast alloys and their strong dependence on the chosen metallurgy. A calcu- lation of the feeding behavior based solely on temperature distributions was not sufficient. For example, large hotspots in iron castings can potentially completely feed themselves, but small hot spots can lead to shrinkage defects. The local shrinking and expansion behavior of a casting can only be calculated under the consideration of the locally developing phases (graphite, austenite, cementite) and their respective contribution to the local shrinking and expansion behavior. The creation kinetics of each phase is therefore considered
throughout the entire progression of the solidification. This means that for cast iron not only is the dominant impact of the alloying elements considered, but also the inoculation and melt quality. Metalcasters use the impact of the inocula- tion or alloying elements for the creation or avoidance of white iron. These are overlaid by the local cooling condi- tions inside a casting. A simulation solely of the macro- scopic solidification and cooling behavior cannot describe this interaction. Therefore, this so-called micromodeling is performed on many materials, considering the amount of any new phase created at any time based on the phenomena described above (Fig. 15 and 16).
Figure 16. Microstructure simulation of cast iron alloys provides a multitude of quantitative information about local structures, i.e Ferrite/Pearlite distribution. /6/
Figure 17. Distortion of a structural part in a diecasting die. The alloy specific contraction behavior in solidifying and cooling castings can lead to plastic (remaining) deformations, at room temperature (exaggerated display). /7/
Figure 18. Prediction of cracks in a casting. The contraction of a casting and the constriction of the resulting movement of it at high temperatures can lead to very high strain rates. At the same time, the material is often brittle and cannot sustain any loads. This leads to cracks when high stresses (tension) are present at high temperatures (this often happens in places that show compression at room temperature, which is puzzling).
International Journal of Metalcasting/Spring 10 15
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