Ultra-fast tempering cycles, combining a rapid heating rate (R (H) = 300 A degrees C/s) from room temperature to a peak temperature within the range 400-700 A degrees C and subsequent rapid cooling, were performed on a Fe-Mn-C martensitic steel. The influence of the peak temperature reached during the cycle was determined on both the tensile properties of the steel and on its microstructure. The mechanisms controlling the microstructural evolution occurring during rapid tempering were studied by combining both TEM observations and 3D reconstructions by FIB/SEM. A theoretical analysis coupled with the acquired experimental data was then proposed to explain the evolution of mechanical properties. The results obtained support the assumption that carbide precipitation during fast tempering plays a key role in the evolution of mechanical properties.