High-Manganese Steels (HMnS) are promising candidates to be used for additive manufacturing (AM) processes, besides austenitic stainless steels such as 316L or 304L. This class of steels is characterized by outstanding mechanical properties for a wide range of industrial applications, e.g. for automobile and aerospace has been impeded so far due to their comparatively high alloying and processing costs. The general concept of HMnS is based on stabilizing the face-centered cubic (fcc) austenite phase with a high amount of Mn (15–30 wt.%) and additions of C (0.05–1 wt.%) and Al (0–3 wt %). The low SFE hence is responsible for the activation of additional deformation mechanisms, such as deformation twinning (TWIP) and martensite formation (TRIP). Further increase in aluminium concentration affects SFE and can lead to stabilization of the ferrite in the as built state. The microstructure and deformation mechanisms were studied using the neutron diffraction, EBSD and modeling.