Paper deals with phase transformations and austenitizing behaviour of the OCHN3MFA high strength steel. Dilatation analysis of a series of samples was performed at various cooling rates, selected in the range from 100 °C s^-1 to 0.01 °C s^-1. Acquired experimental data were used to evaluate dilatometric curves in order to map the temperature ranges of austenite to ferrite, bainite or martensite. Then, all experimental samples from dilatometric analysis, were subjected to microstructural analysis and hardness measurements to characterize the microstructure and hardness for each tested heat treatment regime.