Optimization of the fatigue behavior of TWIP steels through monotonic pre-straining

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The development of light-weight structures featuring high specific strength is in focus of industrial and academic research. Due to the combination of high strength and extraordinary ductility TWIP-steels (TWinning Induced Plasticity) are a promising candidate for light-weight design. In these steels twinning can be observed already at low degrees of deformation leading to delayed necking due to dynamic Hall-Petch effect. Using TWIP steels weight reduction of the body in white, eventually decreasing the energy consumption, can be achieved. High crash performance is another essential factor qualifying materials for automotive applications. This and other important aspects such as drawability and the feasibility of cold working at high remaining ductility are met by the TWIP steels, as well.However, the basic understanding of the deformation behavior of TWIP-steels induced by the interaction of different microstructural features under variable operating conditions, i.e. monotonic and cyclic loading at different temperatures, is not sufficient. The active deformation mechanism, determined through the stacking fault energy (SFE), is the key parameter for evaluating the nature of deformation. The possible mechanisms in the high manganese steels are TRIP (TRansformation Induced Plasticity), TWIP and/or slip.In line with the investigations conducted so far and based on the results currently available, the continuation of this research project is aiming at deepening the understanding of the deformation mechanisms active in the TWIP-steels and their interactions especially at different temperatures. A thorough test program will be employed in order to characterize the mechanical property - microstructure relationships under cyclic loading at different temperatures and in different microstructural conditions.