A dilatometric study of medium carbon Cr-Mn-Mo steel 4140 with a different chemical composition was carried out. The CCT diagrams of the austenite transformation were plotted, and the temperature-time ranges of the formation of the structural components were determined. A metallographic study of the steels cooled at various rates was performed. The dependence of the hardness of the studied steels on the tempering temperature was established, and the mechanical properties of the heat-treated steels were determined. The cooling curves of a drill pipe with a wall thickness of 30 mm during the heat treatment were determined using the numerical simulation.