Transformation plasticity in high strength, ductile ultrafine-grained FeMn alloy processed by heavy ausforming

•Heavy ausforming leads to a fully austenitic ultrafine-grained FeMn microstructure.•The ultrafine-grained FeMn alloy shows a large ductility, with no need of annealing.•The high strain hardening capacity is due to the epsilon-martensitic transformation.•Non-basal slip in the epsilon-martensite enables significant plastic co-deformation.•The transformation-plasticity interaction is analyzed by a micromechanical model.