The microstructure and mechanical properties of NiCrMoV-and NiCrSi-alloyed medium-carbon steels were investigated after multiple tempering.After austenitising,the steels were hardened by oil quenching and subsequently double or triple tempered at temperatures from 250 to 500 ℃.The samples were characterised using scanning electron microscopy and X-ray diffraction,while the mechanical properties were evaluated by Vickers hardness testing,V-notched Charpy impact testing and tensile testing.The results showed that the retained austenite was stable up to 400 ℃ and the applied multiple tempering below this temperature did not lead to a complete decomposition of retained austenite in both steels.It was also found that the microstructure,hardness and impact toughness varied mainly as a function of tempering temperature,regardless of the number of tempering stages.Moreover,the impact toughness of NiCrMoV steel was rather similar after single/triple tempering at different temperatures,while NiCrSi steel exhibited tempered martensite embrittlement after single/double tempering at 400 ℃.The observed difference was mainly attributed to the effect of precipitation behaviour due to the effect of alloying additions in the studied steels.