Influence of microstructure and phase constitution on the deformation and damage behavior of high-manganese lightweight steels under cyclic loading

由于其降低的密度和出色的机械性能，高锰轻质钢在机动领域的结构应用中具有巨大的潜力。由于具有较高的比强度和良好的成形性，这些钢材可用于设计与碰撞相关的车身结构，从而提高安全性，减轻重量，从而提高燃油效率，减少二氧化碳排放。优异的力学性能可归因于独特的变形机制，如滑移带细化诱发塑性（SRIP）或动态滑移带细化（DSBR）。为了实现高锰轻质钢的可靠、广泛使用，对其疲劳性能进行深入分析是必不可少的，因为这些钢的许多设想应用将在使用寿命期间经历循环加载。因此，在不同的疲劳寿命状态下，这些钢的不同组织和相组成对疲劳行为的影响尤为重要。然而，对当前最新技术的分析表明，除了少数例外，对高锰轻钢的疲劳性能没有系统的研究，最终，不同相对不同范围内疲劳寿命的影响尚未得到充分解决。关于在不同疲劳寿命状态下，循环荷载作用下塑性变形所占比例变化的变形机制分析，在公开的文献中没有全面的数据。鉴于这种知识的缺乏，设计了目前的项目。以Al14、6C4、9Fe53、6Mn26、9合金为例，深入研究了高锰轻钢在不同疲劳寿命下的循环加载行为，并探讨了不同相的作用以及相关的不同变形机制。该项目中使用的分析方法将允许理解相对于所研究合金的不同相结构的循环变形响应。此外，不同主动变形机制的影响，取决于不同程度的塑性变形，将为高锰轻钢在循环载荷下的性能提供重要的见解。在这些调查的基础上，应提出适用于可能应用要求的轻钢的使用建议。

Due to their reduced density combined with outstanding mechanical properties, high-manganese light-weight steels offer a great potential for structural applications in the mobility sector. Enabled by the high level of specific strength and good formability, these steels allow for the design of crash-relevant body structures with increased safety leading to a weight reduction and, thus, to an improved fuel efficiency as well as a reduced CO2 emission. The excellent mechanical properties can be attributed to unique deformation mechanisms, such as Slip-band Refinement Induced Plasticity (SRIP) or Dynamic Slip-band Refinement (DSBR). In order to allow for a reliable, wide-spread use of high-manganese light-weight steels, an in-depth analysis of the fatigue behavior is essential, as many of the envisaged applications for these steels will undergo cyclic loading during service life. Thereby, the influence of different microstructures and phase constitutions of these steels on the fatigue behavior in various fatigue life regimes is particularly in focus.However, analysis of the current state-of-the-art reveals that, with a few exceptions, there are no systematic studies on the fatigue properties of high-manganese lightweight steels and, eventually, the influence of different phases on the fatigue life at various ranges has not yet been adequately addressed. Regarding analysis of deformation mechanisms occurring under cyclic load as a function of the varying proportion of plastic deformations in the diverse fatigue life regimes, no comprehensive data can be found in open literature.In light of this lack of knowledge the present project was designed. Exemplarily using the alloy Al14,6C4,9Fe53,6Mn26,9, the behavior of a high-manganese lightweight steel under cyclic loading in different fatigue life regimes will be thoroughly investigated, and the role of the different phases as well as the associated different deformation mechanisms will be explored. The analysis methods used in the project will allow for an understanding of the cyclic deformation response with respect to the different phase constitutions of the studied alloy. In addition, the influence of the different active deformation mechanisms, depending on the varying degrees of plastic deformation, will provide important insights into the properties of high-manganese lightweight steels under cyclic loading. Based on these investigations, recommendations for the use of lightweight steels, adapted to the requirements of possible applications, shall be given.