The study was undertaken to gain insight into the micro-mechanisms controlling plasticity at the micrometer scale of elastic-plastic metallic alloys. Dynamic nano-indentation tests, where a small harmonic force amplitude is superimposed during loading, referred to as continuous stiffness measurement (CSM), were performed to study contact damping in martensitic stainless steels with different heat treatments. The nano-indentation experiments were analyzed according to a specific protocol developed in this study, which results from a careful dynamic characterization done over a wide range of materials with significant different plastic flow properties, to separate the effect of the instrument from those of the material. The method was then applied to the tempered martensitic steel Eurofer97 in different tempering conditions. Based on the dynamic contact analysis developed for visco-elastic materials, we propose a new interpretation of the damping coefficient for materials like Eurofer97 dominated by an elastic-plastic behavior. The loss factor and the nano-hardness were correlated with the propensity of the material to plastic deformation, characterized by the average flow stress determined from tensile tests.