The structure and tensile mechanical properties of sparingly alloyed steel 20Kh3 are studied after quenching and tempering at different temperatures. Comparative analysis of the load-extension curves in individual deformation stages and of the fracture zones after tempering at 250 - 650°C is performed. It is shown that the low ductility margin of steel 20Kh3 after high-temperature tempering is a result of precipitation of special carbides both inside grains (Cr7C3) and over grain boundaries (Cr7C3, Cr23C6) controlling the density and mobility of dislocations.