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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. more...

Steels with adjustable austenitic transformation during the exploitation (RAPE) are designed for applied in the temperature range of 800 – 950 °C, which corresponds to the austenitic structure, but at the lower temperature range (630 – 650 °C) tempering fragility of the second kind occurs, which makes it difficult to operate. This is inconvenient when the die tool works in a wide range of temperatures during deformation of various metals and alloys. An improved steel composition (4H4N5M3F2) (RAPE) for press molds for hot pressing of copper and its alloys at temperatures of 630 – 650 °C is proposed. Steel was obtained by electroslag remelting, it was heat treated and the properties were determined. It is shown that the heat resistance of the investigated steel is higher by 2 HRC than the heat resistance of steels grade 4H5MF1S and 3H3M3F, which are used under the same operating conditions. The yield strength and impact strength of steel 4H4N5M4F2 considerably exceeds the characteristics of steel 3H3M3F (high –grade rolled products). The annealing temperature limits, which allow obtaining the necessary technological properties of steel, were established. It is shown that the steel structure consists of two areas: dark (obviously it is released martensite) and light (the area with a lower content of the carbide component). With an increase in tempering temperature from 640 to 660 °C, the hardness (HV) of the dark and light components decreases from 478.6 to 459.8 and from 427.8 to 376.0, respectively. The heat resistance of the investigated steel after quenching and tempering in optimal conditions increased to 650 °C (41 HRC). more...

The paper examines the mechanisms that contribute to the strength of green compacts produced and tested in different thermal conditions (different homological temperatures of Sn, Zn, Cu, Ni, and Mo powders compacted and tested in normal conditions). The role of powder particle shape is demonstrated using scanning electron microscopy to analyze images of the particles and fracture patterns of the compacts. Partial plastic fracture is found only in the Sn powder sample. When plastic powders with irregular, branched particles (Cu, Ni) are compacted, the mechanism of adjusting particle surfaces to one another prevails and leads to all three mechanical components: interlocking, entangling, and seizing. When plastic powders with spherical particles are compacted, deformation of particles prevails. The ratio of the tensile strength of compacts (σb.i) determined indirectly to the tensile strength (σb) of particulate material shows a semilogarithmic dependence on the ratio of compacting pressure (P) to the yield stress (σ0.2) of the particulate material. The dependence of the ratio of σb.i to the elastic modulus on the homological temperature of compacting and testing divides into two linear dependences for spherical and nonspherical particles. more...

Modern approaches to calculating the strength of green compacts by van der Waals forces (σVW) are reviewed. Respective components (σVW) are calculated and green tensile strength (σtl.av) is experimentally determined for test powders of metals (Al, Zn, Cu, Ni, and Mo) and one nonmetal (FeSi). Comparison of σtl.av/σVW ratios shows that σtl.av and σVW are of one order for the atomized zinc powder, and σVW is greater than σtl.av for the atomized copper powder, though σtl.av is greater than σVW by two to three orders for most powders with irregular shape of particles. This difference can be attributed to the effect of shape and mechanical interlocking or seizure of particles when compacted. To predict the green strength, it is necessary to take into account both the shape of particles (or relative apparent density of the powder) and the forming temperature. more...