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

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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.