Optimized Durability Prediction of Cast Iron Based on Local Microstructure

Abstract

The microstructure of cast iron is decisively influenced by the composition, the applied metallurgy and the process conditions. Differences in microstructure mainly influence the local mechanical properties. In conventional durability predictions, local microstructure and local defects in the casting are not taken into account. The assumption of homogeneous material properties applying one single material dataset for the prediction of fatigue strength usually leads to a misinterpretation in the assessment of local risks. Furthermore, the material potential of the casting will not be used in full. Safety margins result in an over design and unnecessarily high weight of the component as well as increased casting part costs. The designer can only benefit from the potential of the material cast iron, if the real spectrum of local material properties is considered in durability calculations. Current casting process simulation tools allow the prediction of local microstructure and resulting static mechanical properties as a function of alloy composition, applied metallurgy and local solidification and cooling conditions. Within a German research project, the link between casting process simulation and cyclic material properties was established for different cast iron materials for the first time. S–N curves (Woehler curves), which depend on local microstructure close the gap between casting process simulation and lifetime analysis. This innovative approach leads to improvements in lifetime predictions. It was shown that the consideration of local fatigue strength based on this innovative approach leads as well to an increasing number of cycles to failure as to a correct prediction of the location of crack initiation. Compared to the conventional design of castings, a substantial qualitative and quantitative improvement in assessing the real performance of cast iron materials can be realized.