It is known that the mechanical properties of steels are dependent on the final microstructure resulting from phase transformation during heat treatments. Hot rolled mine support profiles are produced generally from unalloyed quality steels. After the hot rolling, heat treatments of quenching and tempering result in a tempered martensite microstructure with high strength and toughness. The retained austenite phase may also be expected in the microstructure due to the lack of alloying elements. In this study a microstructural characterization of a mine support profile is carried out before and after the quenching and tempering to investigate the effect of heat treatments on the microstructure. A dilatometric analysis is performed to detect the phase transformation temperatures. Dilatometric analysis is carried out at different cooling rates from austenite phase region. Depending on the different cooling rates, ferrite, pearlite and bainite phases are determined using dilatation curves, light microscope, and Vickers hardness tests. The results indicate that critical temperatures can be determined by dilatometric analysis.