Application of Austempered Ductile Iron in Hydraulic Components with Dynamic Loads

等温球墨铸铁（ADI）和等温球墨铸铁（IDI）是热处理球墨铸铁（GJS）。ADI的热处理包括奥氏体化、淬火和等温等温回火等步骤。在奥氏体化过程中，奥氏体富含碳。在等温等温回火过程中，奥氏体部分转变为铁素体，剩余奥氏体的碳富集量增加，使其在室温下保持稳定。另一侧的IDI是临界间奥氏体化，然后进行控制冷却。以珠光体形成的方式选择冷却速率。因此，IDI的显微组织由预共析铁素体和珠光体组成。与基材（GJS）相比，ADI的抗拉强度或伸长率可以增加两倍或更多。IDI的力学性能介于ADI和球墨铸铁之间。因此，这些材料对于具有液压负载的组件（如阀门控制时钟）很有趣。由于这些部件需要不断增加的液压压力和恒定的设计空间，因此标准球墨铸铁的疲劳性能的增加受到限制。因此，该研究项目的主要目的是通过应用ADI来提高暴露在动态油压下的部件的疲劳性能。作为一种可能具有成本效益的替代方案，IDI也将为此应用进行测试。在大量前期工作的基础上，用中子衍射来表征所用材料的热处理。前期工作和新数据的结合，可以根据演示器的要求做出合理的合金决策。将采用静态和动态试验制定适当的热处理策略。在这些结果的基础上，将生产ADI和IDI样品，并在水动力载荷下进行测试。大量动态试验的样品将用于分析动态载荷作用下奥氏体向马氏体转变的过程。将对断裂试样进行金相和衍射分析，以研究相变与裂纹扩展之间的关系。

Austempered ductile iron (ADI) and isothermed ductile iron (IDI) are heat treated ductile irons (GJS). The heat treatment of ADI consist of the steps austenitising, quenching and isothermal austempering. During the austenitisation the austenite enriches with carbon. As the austenite partially transforms into ferrite during the isothermal austempering, the carbon enrichment of the remaining austenite increases making it stable at room temperature. IDI on the other side is intercritically austenitised followed by a controlled cooling. The cooling rate is selected in a way that pearlite forms. The microstructure of IDI therefore consist of proeutectoid ferrite and pearlite.Compared to the base material (GJS) the tensile strength or elongation of ADI can be increased by factor two or more. IDI shows mechanical properties between those of ADI and ductile iron. These materials are therefore interesting for components with hydraulic loads such as valve control clocks. As increasing hydraulic pressures along with constant design spaces are required for these components, the increase of fatigue properties is limited with standard ductile irons.The principle aim of the research project therefore is to increase the fatigue properties of components, which are exposed to dynamic oil pressures by the application of ADI. As a possible cost-effective alternative IDI will also be tested for this application.On the basis of extensive preliminary work, the heat treatment of the used materials will be characterised by neutron diffraction. The combination of preliminary work and new data allows a sound alloy decision with respect to the requirements of the demonstrator. An appropriate heat treatment strategy will be developed using static and dynamic tests. On the basis of these results ADI and IDI samples will be produced, which will be tested under hydrodynamic loads.The samples of the numerous dynamic tests will be used for the analysis of transformation of austenite to martensite under dynamic loads. The fractured samples will be analysed using metallography and diffraction in order to investigate the supposed correlation of transformation and crack propagation.