Failure mechanisms in solid solution strengthened ductile cast iron

球墨铸铁是一种成熟的材料，由于其优异的铸造性能，高回收率和低成本而脱颖而出，同时提供最佳的机械性能，这就是为什么它被用于许多应用。除了传统牌号外，新开发的牌号采用硅固溶强化，具有进一步提高强度的潜力，同时保持较高的断裂伸长率。锻造部件可以用固溶强化铸铁替代，并且可以更有效地生产。然而，设计人员迄今为止一直不愿意使用这种材料，因为它会根据温度和载荷情况表现出不可预测的脆性断裂行为。我们自己为这个项目所做的准备工作表明，这与B2-超结构的形成特别相关，在硅含量升高时，可以在铁素体基体结构中观察到越来越多的B2-超结构。在本研究项目中，将从根本上研究和解释铁素体基体结构中超结构的局部分布及其对失效机制和断裂行为的影响。为此，硅含量将逐步变化，因为超结构的形成基本上取决于硅梯度，其在奥氏体基质中凝固期间围绕石墨球形成。此外，通过添加合金元素，如铝，对形成的超结构的硅梯度的减少的影响进行了研究。为了使实验获得的知识可用于进一步的发展，数值模拟方法被用来创建一个微观结构模型，在该模型中，可以映射和预测机械应力下的失效机制的微观结构中的冶金梯度的影响。综合模拟方法的目的是能够首次模拟铸铁的整个过程和机械性能，同时考虑到局部冶金梯度，并使其可用于未来的发展。通过结合两个研究部门在该项目中的专业知识，将达到铸铁材料进一步发展的里程碑，这有望在目前的技术水平上具有明显的方法优势，并允许未来面向应用的高强度铸铁开发具有高断裂韧性。

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.