This study analyzes the microstructural and mechanical evolution of K100 tool steel after applying a sequential heat treatment consisting of austempering at 270 °C, followed by tempering at 160 °C–220 °C. Optical microscopy and mechanical tests were used to evaluate the phase transformations and tensile behavior. The results show a gradual morphological change in the bainitic structure, along with partial carbide spheroidization, as the tempering temperature increased. Notably, tempering above 200 °C produced an optimal balance between strength and ductility, significantly reducing internal stresses while maintaining high hardness levels. This dual treatment strategy outperforms traditional quenching-tempering processes in terms of dimensional stability and energy absorption capacity.