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The results of research of structural steel brand 4Kh4N5М4F2 after heat treatment are given. Manifestations of tempering brittleness at a temperature of 450-500 °C, associated with the maximum value of the parameter «a» of the crystal structure during the formation of a solid substitution solution in the system "Fe-C". The connection between the peculiarities of the crystal structure of the studied steel and the complex of physical and mechanical properties is established. The maximum value of the parameter «а» (a = 0.28848 nm) of the elementary cell of martensite crystal lattice reflects the maximum saturation of the α-solid solution, which increases the resistance of the crystal lattice to deformation, increase the hardness of tempering martensite (up to 56 HRC), change the physical structure sensitive value (increase in specific conductivity to 0,200 Om•mm2/m), increase the tensile strength, reduce the impact strength (up to 15 J/cm2) and increase the brittleness at temperatures of 450-500 °C. The possibility of using matrices (steel 4Kh4N5М4F2, without forging technology) for hot deformation of aluminum alloy AK7ch, which during operation does not reach the temperature of brittleness (above 460 ºC), is demonstrated. Keywords: die steel, crystal structure, heat treatment, physical and mechanical properties.

Tempering brittleness of die steel 4Kh4N5М4F2