AbstractIn order to produce extremely high strength values without impairing the impact properties, the microstructures of two low-carbon microalloy steels were modified substantially by carefully designed combinations of hot working and heat treatment. The interplay of several microstructural processes in unconventional variants of thermomechanical treatment was investigated systematically. The experiments were carried out in plane-strain compression using the computer controlled hot-deformation simulator‘WUMSI’. The results indicate that for optimizing mechanical properties the variants found most suitable were those which lead to a fine microstructure by quenching or which take advantage of grain refining caused by additional reaustenitizing. Furthermore, the controlled superposition of age hardening and subsequent deformation brought about increasing yield and tensile strengths together with some reduction in shelf energy. The beneficial effect of microstructure refinement was more pronounced in the pearlite-reduced Ti steel, whereas the straining of an age-hardened microstructure could be exploited extensively in the acicular-ferritic Nb–Mo steel.MST/55