The assessment of the effect of tempering temperature on hardness and impact toughness of a 56NiCrMo7 grade hot work tool steel was presented in the paper. It has been found that the investigated steel, after quenching in oil from 800 degrees C, softens quite slowly upon tempering within the range between 100 and 675 degrees C, which was confirmed not only by hardness measurements but also by observed changes occurring in its microstructure, whereas the impact energy (KV) absorbed by the test specimen increases with temperature, achieving > 66J after tempering at 675 degrees C. The changes observed in the character of the fracture surfaces allows of interpretation of the impact test results for the whole range of tempering temperatures.
