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The results of the preliminary heat treatment effecting in a medium with a high oxygen content on the microstructure and mechanical properties of structural steels are presented. It is shown that the usage of preheating in the glass mass in the range of (Ac130°C) – Ac1for steels of grades 50 and 40H leads to the formation of a structure with dispersed granular pearlite and crushed excess ferrite precipitates. Such a structure, when heated for quenching, provides rapid formation of a homogeneous austenite and a delay in the growth of austenite grain, which provides the best combination of strength and plasticity after the final heat treatment. It is established that the tensile strength increases 1.2-1.3 times while maintaining the plasticity characteristics. The reliability of the obtained estimates of the mechanical property characteristics is confirmed by the results of a statistical analysis.