Application of Austempered Ductile Iron in Hydraulic Components with Dynamic Loads

等温淬火球墨铸铁(IDI)和等温淬火球墨铸铁(ADI)属于热处理球墨铸铁。ADI的热处理包括奥氏体化、淬火和等温等温淬火三个步骤。在奥氏体化过程中，奥氏体富含碳。在等温等温淬火过程中，随着奥氏体部分转变为铁素体，残余奥氏体碳的富集量增加，使其在室温下保持稳定。在另一端，IDI进行临界奥氏体化，然后进行受控冷却。冷却速度是以珠光体形成的方式选择的。因此，IDI的组织由先共析铁素体和珠光体组成，与母材(GJS)相比，ADI的抗拉强度或延伸率可提高一倍或两倍以上。IDI的力学性能介于ADI和球墨铸铁之间。因此，这些材料对于阀门控制时钟等具有液压负载的部件很有意义。由于这些部件需要不断增加的液压和恒定的设计空间，因此标准球墨铸铁的疲劳性能的提高是有限的。因此，研究项目的主要目的是通过应用ADI来提高承受动态油压的部件的疲劳性能。作为一种可能的具有成本效益的替代IDI，还将测试这种应用。在广泛的前期工作的基础上，所用材料的热处理将以中子衍射为特征。初步工作和新的数据相结合，可以根据演示者的要求做出合理的合金决定。将通过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，将产生ADI和IDI样品，并在水动力载荷下进行试验。大量动态试验中的样品将用于分析动态载荷下奥氏体向马氏体的转变。用金相和衍射法对断口样品进行分析，以研究相变和裂纹扩展之间的假设相关性。

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.