Joachim Mayer^1,2, Maryam Beigmohamadi², Marta Lipinska-Chwalek^1,2 and James E.Wittig³

¹Central Facility for Electron Microscopy, RWTH Aachen University, Aachen, Germany
²Ernst Ruska Centre, Forschungszentrum Jülich, Germany
³Interdisciplinary Materials Science, Vanderbilt University, Nashville TN, 37235 USA

Recently developed high-manganese steels exhibit an exceptional combination of strength and ductility and show great promise for structural applications. Understanding the relationships between manganese and carbon content, microstructure, temperature, defect formation and strain-hardening behavior is critical for further optimization of these steels. We investigated the influence of alloy content, temperature and deformation behavior on the microstructural evolution of an austenitic Fe-14Cr-16Mn-0.3C-0.3N alloy showing twinning induced plasticity (TWIP) and of a two-phase nanostructured Fe-30.5Mn-8Al-1.2C alloy exhibiting microband induced plasticity (MBIP). The twinning induced plasticity (TWIP) effect enables designing austenitic Fe-Mn-C based steels with >70% elongation at an ultimate tensile strength >1 GPa. High resolution TEM and STEM images of the planar defects will be presented and detailed investigations revealed insight in the atomistic structure of defects and defect/dislocation interaction. In the MBIP alloys, regularly spaced coherent precipitates of the κ-Phase were found, which cause the unique properties of these materials.