Prediction of Microstructure and Local Mechanical Properties for a CGI Crankcase

Non-uniform cooling conditions within a casting lead to locally differing microstructures, which result in locally differing mechanical properties. These have a tremendous impact on the behavior of the parts under their application load conditions and regarding their life time. The virtual development of castings can, therefore, only be effective when the process simulation is integrated into its design and application analysis (Finite Element Analysis [FEA]) procedure. Closing the gap between the currently available results of casting process simulation tools and the local cyclical material properties of cast iron materials were evaluated within the scope of the German research project MABIFF. This paper will present the initial results for compacted graphite iron (CGI). CGI has essentially two strength relevant microstructure variables: the shape and size of the graphite particles, as well as the ferrite/pearlite ratio and distribution in the matrix. To accurately simulate the development of the microstructure it is necessary to understand and mathematically describe the metallurgical process during the solidification and the eutectoid transformation. Therefore, the available simulation models describing the solidification were expanded and a new model for the prediction of the ferrite/pearlite distribution was developed. These simulation models were validated on test castings and the Audi 3.0l V6 TDI crankcase made of CGI. This paper compares and discusses the measured and calculated microstructure distribution and its impact on durability of the castings.