OPTIMIZING HEAT TREATMENT MODES WITH ALLOWANCE FOR SPECIFIC ELECTRIC CONDUCTIVITY OF CAST DIE STEEL 4KH4N5М4F2
10.33815/2313-4763.2021.1.24.129–135
Abstract
The results of research on determination of structurally sensitive value (conductivity) after heat treatment (hardening and tempering) of steel (without deformation-forging) with adjustment of austenitic transformation during operation of the brand 4Kh4N5M4F2 have been disclosed. It has been established that the minimum value of the parameter – specific electric conductivity was being determined at optimized modes of heat treatment of the investigated steel. Thus, for the optimal value of the tempering temperature of steel (1100 ºC), the specific electric conductivity was 0,075 Ohm‧mm2/ m, and at tempering (595 ºC) – 0,0415 Ohm‧mm2/m. The relationship between the specific electric conductivity and the parameter of the crystal cell of martensite, hardness and toughness of hardened steel. It has been established that in the process of primary recrystallization at temperatures above 1110 ºС, the conductivity of steel decreases. It has been proved that during reheating (tempering), the conductivity in steel increases, and the structurally sensitive mechanical characteristic (impact strength) changes intensively, which increases twice in the range of tempering brittleness temperatures of 475±15 ºС. Since its anomaly occurs at that kind of temperature range, the decrease is up to 15 J/cm2 and the parameter of the crystalline cell of martensite increases (2.8847‧10-1 nm). The optimized mode of hardening of 1095 ºС and tempering of 590 ºС of the investigated steel, enabled to increase impact strength to 30 J/cm2 and increased conductivity in the range of temperatures of tempering brittleness of the first kind. This makes it possible to increase the service life of the press tool (die) made of steel 4Kh4N5M4F2 for hot deformation of aluminum alloy in the temperature range of 450-500 °C.
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