Influence of strain path changes during cup drawing on the twinning activity in TWIP steels investigated by electron channeling contrast imaging

The present work is focusing on the deformation mechanisms of two TWIP steels with different susceptibility towards hydrogen embrittlement, namely a Fe22Mn0.6C (high susceptibility) and an X40MnAlSi20-1.5-1 (low susceptibility). The complex cup drawing process was separated into successive strain paths, namely plane strain compression, bending, and unbending. Each of them was experimentally remodeled and the microstructure was investigated. With this approach, it was possible to monitor the processes leading to the final, critical, microstructure of the material. The microstructural investigation in this work was carried out using electron channeling contrast imaging (ECCI). Main features and phenomenon of TWIP steels were investigated and their appearance in the ECCI mode was validated using TEM and EBSD. ECCI could be established as a scale bridging method and a powerful tool to investigate crystal defect structures in bulk materials, giving deep insight into their crystallography if combined with EBSD.