The increasing interest in nano-crystalline materials in the past years is the consequence of exceptional mechanical (e.g. high tensile and fracture strengths) and physical (e.g. magnetic) properties. One widely reported phenomenon is the hardening of these materials after annealing. This behaviour is mostly ascribed to the increased fraction of grain boundaries, which act as sinks for dislocation movement and solute diffusion, therefore decreasing the number of mobile dislocations and increasing the hardness. Irradiation on the other hand is also well known to increase the hardness of a material but with different mechanisms, such as introduction of defects (e.g. dislocation loops) and impurity elements (e.g. Hydrogen). This work concentrates on the question if the irradiation of a material can counteract the decreased dislocation density achieved by previous annealing in nano-crystalline austenitic stainless steel (Böhler A220). To investigate the impact of radiation induced defects without activating the material, protons with an energy of approximately 1 MeV are used, which results in a penetration depth of the ions in matter of around 6–8 μm. Therefore, it is necessary to utilize micromechanical investigation techniques, such as in-situ microcompression testing in a scanning electron microscope and nanoindentation to compare mechanical properties and deformation behaviour of annealed and non-annealed samples with and without irradiation damage, respectively. We were able to distinguish differences in mechanical behaviour and deformation mechanisms of the different material conditions.