A dilatometric study of steel 45Kh5MF used for making rolling mill rolls is performed. The results of the dilatometric and metallographic analyses are used to determine the kinetics of the pearlitic transformation in the steel under continuous cooling. The developed method of numerical simulation of structural transformations under continuous cooling is used to solve the inverse problem and to plot a computational isothermal diagram of decomposition of supercooled austenite in steel 45Kh5MF in the range of pearlitic transformation. To check the solution obtained an experimental isothermal diagram of decomposition of austenite in steel 45Kh5MF in the pearlitic range is plotted. The data of both diagrams match accurately enough.