Failure mechanisms in solid solution strengthened ductile cast iron

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Nodular cast iron is a well-established material that stands out due to its excellent casting properties, high recycling rate and low costs, while at the same time offering the best mechanical properties, which is why it is used in numerous applications. In addition to the conventional grades, the newly developed grades, which are solid solution strengthened with silicon, have a high potential to further increase the strength while maintaining high elongation at break. Forged components can be substituted and can be produced more resource-efficiently with solid solution-strengthened cast iron. However, designers have so far been reluctant to use this material because it can exhibit unpredictable brittle fracture behaviour depending on temperature and load case. Our own preparatory work for this project has shown that this is particularly related to the formation of a B2-superstructure, which can be observed increasingly in the ferritic matrix structure at elevated silicon contents. In this research project, the local distribution of the superstructure in the ferritic matrix structure as well as its influence on failure mechanisms and fracture behaviour will be fundamentally investigated and explained. For this purpose, the silicon content is to be varied in steps, since the formation of the superstructure depends essentially on the silicon gradient, which forms around a graphite nodule during solidification in the austenitic matrix. In addition, the influence of the reduction of the silicon gradient by adding alloying elements, such as aluminium, on the formation of the superstructure is to be investigated. In order to make the experimentally gained knowledge usable for further development, numerical simulation methods are used to create a microstructure model in which the influence of the metallurgical gradients in the microstructure on the failure mechanisms under mechanical stress can be mapped and predicted. The aim of the integrative simulation approach is to be able to simulate the whole process and mechanical properties for cast iron for the first time, taking into account local metallurgical gradients, and to make it usable for future developments. By combining the expertise of the two research departments in this project, a milestone in the further development of cast iron materials will be reached, which promises a clear methodological advantage over the current state of the art and allows future application-oriented high-strength cast iron developments with high fracture toughness.