The aim of the performed experiments was to determine the influence of a cooling rate on the evolution of microstructure and hardness of the steel 27MnCrB5. By using dilatometric tests performed on the plastometer Gleeble 3800 and by using mathematical modelling in the software QTSteel a continuous cooling transformation diagram for a heating temperature of 850°C was constructed. Conformity of diagrams constructed for both methods is relatively good, except for the position and shape of the ferrite nose. The values of hardness, temperatures of phase transformations and the volume fractions of structural phases upon cooling from the temperature of 850°C at the rate from 0.16°C · s–1 to 37.2°C · s–1 were determined. Mathematically predicted proportion of martensite with real data was of relatively solid conformity, but the hardness values evaluated by mathematical modelling was always higher.

The work deal with an assembling and comparing of transformation diagrams of two low-alloy steels, specifically 16MnCrS5 and 20MnCrS5. In this work, diagrams of the type of CCT and DCCT of both steels were assembled. Transformation diagrams were assembled on the basis of dilatometric tests realized on the plastometer Gleeble 3800, of metallographic analyses and of hardness measurements. In addition, for comparison, the transformation diagrams were assembled even with use of the QTSteel 3.2 software. Uniform austenitization temperature of 850°C was chosen in case of both steels and even both types of diagrams. In case of both steels, an influence of deformation led to expected acceleration of phase transformations controlled by diffusion and also of bainite transformation. In both cases, the kinetics of martensitic transformation was not significantly affected by deformation.