Показано, що структура загартованої сталі 40Х3Н5М3Ф при нагріванні від кімнатної температури до температури експлуатації (800С) змінюється: мартенситна структура перетворюється на аустенітну. Залежність кількости аустеніту від температури близька до експоненційної. Підтверджено, що в інтервалі температур експлуатації (750-800С) дослідна сталь має аустенітну структуру з невеликою кількістю карбідної складової (1,55-1,68%). Ключові слова: сталь, термічне оброблення, структура, твердість. Показано, что структура закалённой стали 40Х3Н5М3Ф при нагреве от комнатной температуры до температуры эксплуатации (800С) изменяется: мартенситная структура превращается в аустенитную. Зависимость количества аустенита от температуры близка к экспоненциальной. Подтверждено, что в интервале температур эксплуатации (750-800С) исследованная сталь имеет аустенитную структуру с небольшим количеством карбидной составляющей (1,55-1,68%).

The ligature for finishing of base steel 3H3M3Ftype for obtaining steel 4H3N5M3Ftype with adjustable austenitic transformation is developed in the article. The phase-structural state of steel in the cast state is investigated. The uniform distribution of alloying components on the body of grains is shown. It was found that the investigated hardened steel is softening above the tempering temperature of 620 °C, because the heat resistance of steel decreases (below 40 HRC). It was developed a 3H3M3F base steel ligature for steel production with adjustable austenitic transformation of 4H3N5M3F brand. Ingots (ligature of the Fe―Ni―Mo―V―Mn system) weighing 25 kg were obtained. The ligature was obtained by means of an induction furnace in a casting mold. The temperature of the metal in the furnace before release was 1550 °C. The duration of refining did not exceed 20 minutes. The phase-structural state of cast steel is studied. The uniform distribution of alloying components on the body of grains is shown, as well as the absence of coarse carbide eutectic in metal. This allows to reduce energy-intensive technological operations (diffusion annealing, forging) for the die toolsmanufacture. The presence of martensitic structure in the steel in the cast state of the investigated ingot requires the main thermal operation — annealing. It is established that incomplete annealing at a temperature of 750 ± 20 °C under the condition of partial recrystallization of the investigated steel allows to improve the mechanical processing (cutting) for the production of the die tool. It was determined that the investigated hardened steel hardens above the tempering temperature of 620 °C, because the heat resistance of steel decreases (below 40 HRC). Thus, a die tool of the investigated steel for hot deformation, capable of operating up to the temperature of 620 °C. Keywords: steel, ligature, temperature, structure, hardness.

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The results of researches on steel 4H4N5M4F2 modes thermo-deformation processing optimization are given. It is established that incomplete annealing (750 °С ± 20 °С in comparison with full annealing 860 °С) in cast and forged condition promotes to improve the machining of blanks for the manufacture of matrices. It is shown that the use of incomplete annealing, namely partial recrystallization promotes the formation of spheroidized rather than lamellar carbide phase, which leads to a decrease in the characteristics: strength threshold, yield strength, hardness 900 MPa, 800 MPa, 32 33 HRC in the cast state and 1200 MPa, 1050 MPa, 38 39 HRC in forged condition, respectively. This increases the fracture toughness: 180 J/cm2 in the cast state and 130 J/cm2 in the forged state. The optimized mode of forging at the temperature of 1170 ± 20 °С and heat treatment (hardening at 1100 ± 5 °С and tempering at 595 ± 5 °С) of steel 4H4N5M4F2 allowed to increase impact strength five times in comparison with cast experimental steel, and also to increase strength threshold of 100 MPa. Forged steel 4H4N5M4F2 has slightly lower heat resistance compared to cast, which hardens at temperatures above 630 °C during operation of the die steel tool. After operation of the extruder wheels made of investigated forged steel and forged steel 4H5MF1S, which was used at the enterprise in copper processing, the properties of both steels were determined. The investigated forged steel 4H4N5M4F2 is characterized by an increase in the strength threshold by 200 MPa and hardness by 6 HRC. After operation (production of 60 tons of copper products of M1 grade) the tool (wheel extruder) from H13 steel (analog 4H5MF1S) had micro and macrocracks on the side and inner parts, and in the investigated steel 4H4N5M4F2 such defects were absent. Thus, the studied steel is characterized by increased stability. Keywords: steel, heat treatment, forging, structure, physical and mechanical properties.

The intermediate class of steels, which at room temperature belong to the ferritic state, and at operating temperature pass into the austenitic region, are called steels with control of austenitic transformation during operation. The possibility of increasing the service life of such intermediate steels at high temperatures (above the critical point A3) is shown. For the first time, the cast structure and phase-structural state of steel (grade 4Kh3N5М3F) obtained by electroslag remelting were studied. An improved composition of steel (4Kh4N5М3F) for the production of stamping tools for hot pressing of copper, copper and aluminum alloys is proposed. When setting the critical points (A1 and A3) of the investigated steel, which was confirmed by the results of high-temperature X-ray phase analysis, it was possible to optimize the heat treatment (annealing) of steel 4Kh3N5M3F and 4Kh4N5M4F2 in cast and forged condition, which facilitated processing tool. The results of researches on optimization of modes of heat treatment (hardening, tempering) of steel are given. The mechanical properties (strength, toughness, heat resistance) of steel in cast and forged state depending on the tempering and tempering temperature are determined. The tempering brittleness of the experimental steel is determined. An experimental-industrial test of a stamping tool (die dies, extruder parts) made of the investigated steel was carried out. The possibility of using stamped steel with adjustable austenitic transformation for a wide range of operating temperatures of hot deformation of aluminum alloy AK7h (450-500 ºC), copper M1 (600-630 ºC) and copper-nickel alloy MNZh 5-1 (900-950 ºC) with increased service life in comparison with steels of ferrite class 4Kh5МF1S and 3Kh3М3F. Keywords: die steel, composition, thermal treatment, structure, mechanical properties.