


No 3 (2025)
Articles
Wear resistance of corrosion-resistant austenitic high-nitrogen steels 05KH22AG15N8MF and 02KH22AG10N4MF in a cryogenic environment
Abstract
Wear tests were carried out under dry sliding friction conditions in a cryogenic environment on corrosion-resistant high-nitrogen austenitic steels 05Kh22AG15N8MF (0,50% N) and 02Kh22AG10N4MF (0, 55% N), as well as nitrogen-free steels 08Kh18N9T and 03Kh17N13M2. It was established that in terms of wear resistance at increased (7,5 m/s) sliding speed in a self-mated system, high-nitrogen steels 05Kh22AG15N8MF and 02Kh22AG10N4MF surpass steels 08Kh18N9T and 03Kh17N13M2 due to greater solid solution and strain hardening.



Analysis of lead and zinc selective extraction process from EAF dust during carbothermic reduction
Abstract
The selective carbothermic reduction process of lead and zinc oxides from electric arc furnace (EAF) dust in the laboratory horizontal tubular electric furnace in an argon medium with excessive consumption of reducing agent (20 wt.%) during step heating with an exposure for 1 hour at each stage is analyzed. It is established that successive heating and exposure of EAF dust and a reducing agent mixture at temperatures of 1100 and 1200 °C led to the removal of 96.8 and 99.9 rel.% of lead and zinc respectively from the dust. At the same time, iron content in the residue increased to 61.7 wt.%. It is calculated that the introduction of 15.5 wt.% carbon as a reducing agent is sufficient for the reduction of oxides in the considered EAF dust sample. It is experimentally confirmed that when condensate is deposited directly on gas outlet tube in the furnace in an inert medium, the product obtained is mainly in metallic form, while cooling the condensate in traps outside the furnace leads to the formation of lead and zinc oxides, which indicates the oxidation of the material during condensation with air access. The data of X-ray spectral microanalysis of condensate obtained in the furnace in an inert medium indicated the possibility of evaporation from EAF dust no more than 25 rel.% of lead oxide in the gas phase without prior reduction, as well as the fact that lead selective extraction from EAF dust with minimal associated zinc extraction should be carried out at temperatures below 1100 °C.



Features of microstructure formation during continuous aging in granulable nickel-based alloys
Abstract
The influence of continuous aging on the microstructure of the granulated heat-resistant nickel-based alloy EP741NP is considered. The use of continuous aging made it possible to increase the density of γ´-phase particles, reducing their size and the degree of coagulation inside the grains, and to strengthen the boundaries with carbide and boride compounds.



Mechanochemical synthesis of Ni/HfC composite structures
Abstract
The structural-phase evolution of the mechanochemical formation of Ni/HfC mechanocomposites containing 50 and 70 wt.% nickel was studied using X-ray diffraction analysis, scanning electron microscopy, and energy dispersive spectroscopy. It has been shown by X-ray diffraction analysis, that during mechanochemical synthesis in a ternary mixture of elemental powders Ni, Hf and C at a stoichiometric ratio of Hf and C, the formation of hafnium carbide occurred already after 40 s. For both compositions, the crystallite sizes of the nickel rapidly decrease upon mechanical activation for up to 4 min compared to the initial. Intensive formation of hafnium carbide is recorded during mechanical activation with duration of 4–8 minutes. With mechanical activation for 12 and 20 min, the processes of secondary structure formation lead to homogenization of the product and depletion of hafnium carbide in carbon to the composition HfС0.5.



Microstructure and mechanical properties of Cu-Cu2O composites produced by hot pressing of copper powder
Abstract
The article presents results of studying microstructure and mechanical properties of a composite material (Cu-Cu2O). The samples were taken from copper electrical contacts for electric welding machines manufactured by hot pressing PMS-1 powder under of «Uralelectromed». The microstructure was studied using scanning electron microscopy and scanning probe microscopy. The mechanical properties were determined by nanoindentation using the authors’ technique, which involves converting the indentation diagram F(h) into the tensile diagram σ(ε). Metallographic studies have shown a small grain size (~10 μm), the content of cuprite Cu2O inclusions of ~1 μm in size with faceted morphology was close to 20%. The results of measuring the mechanical properties: Young’s modulus E = 119.89±5.75 GPa, hardness HIT = 2.28±0.15 GPa; elastic recovery of the material R = 5.54±2.33%; plasticity characteristic δА = 94.46±2.33%; yield strength σт ≈ 600 MPa. Evaluation of mechanical stresses due to the two-phase nature of the composite material Cu-Cu2O showed that the additional pressure, related to the length of the rupture line, is approximately 50 times greater than the external force, and this can be the main reason for the failure of the products.



Mechanism of the Zr-V alloy nitridization process
Abstract
A sequence of structural transformations characterizing the high-temperature nitridization of a zirconium-vanadium bimetallic billet has been established. The mechanism of nitridization of zirconium-vanadium alloy ZrV2, which is formed during the manufacture of a bimetallic workpiece by electric arc welding, has been established. During high-temperature interaction with nitrogen, the alloy disintegrates, the basis of which is ZrV2 intermetallic compound, with the formation of stoichiometric zirconium nitride ZrN, solid nitrogen solutions and compounds of the composition ZrхVyN1–х–y with simultaneous segregation of vanadium at the grain boundaries of zirconium nitride. The released vanadium diffuses into the area of a solid solution of zirconium with nitrogen in the individual zirconium, forming a solid solution of the composition ZrхVyN1–х–y. The final products of nitridization at the selected temperature are ZrN and Zr0,3V0,6N0,1. Ceramics is a composite consisting of grains of stoichiometric zirconium nitride distributed in ZrхVyN1–х–y with a limiting composition of Zr0,3V0,6N0,1.



Modeling of dissolution of oxide phases zirconium and hafnium in acid solutions
Abstract
The article presents the results of the study of the dissolution kinetics of hydrated zirconium and hafnium dioxides. Experimental dependences characterizing the kinetic regularities of the process were obtained by potentiometric titration of dioxide suspensions in acidified aqueous solutions of potassium chloride. The constants of acid-base equilibria at the dioxide/solution interface were calculated, taking into account which the obtained data were interpreted. The staged nature of the dissolution process was established by modeling and comparative analysis of experimental and theoretical curves. It was shown that the dissolution of dioxides occurs with the formation of intermediate adsorption complexes.



Calculation of the degree of blackness of metallic melts based on the data of technological control of temperature and time during the melting of structural steel grades
Abstract
The article presents the results of calculating the emissivity of iron-carbon melts – semi-finished products formed in steel-smelting units: a converter and an electric arc furnace for further production of carbon structural steel grades. The calculation is based on the model of melt cooling due to radiation. Large samples were used for the calculation. The samples were extracted from the aggregate data of systematic measurements of the melt time and temperature in the technological cycle of steel smelting. It is shown that in the temperature range of 1560–1700 °C, the emissivity value lies in the range from 0.01 to 0.058. The dependence of the emissivity on temperature is of an activation nature and is satisfactorily described by the obtained exponential approximation.



Determining the service life of a metal shell structure using a neural network
Abstract
An effective method for determining the service life of a metal shell structure under variable thermomechanical load is proposed. The stress-strain state of the structure is determined by solving a nonlinear boundary value problem of thermoplasticity for a thin-walled shell of revolution. The service life of structures under variable thermomechanical loads is determined based on the equation of low-cycle fatigue of the material. The application of the presented method is demonstrated using the example of a shell structure designed for high-temperature annealing of electrolytic steel. The temperature of the protective shell during operation can reach 1000 °C. However, this shell is made not of heat-resistant metal, but of St3 steel, which is not intended for use at such an extreme temperature. In the absence of the necessary mechanical parameters for the material of the structure at high temperatures, the prediction method is used. The found service life values for the metal shell with the mechanical parameters of the material at known temperatures are extrapolated to higher operating temperatures using neural networks.



Features of the influence of alternating elastic-plastic deformation on the mechanical properties of metallic materials
Abstract
The study of the effect of elastic-plastic alternating deformation on the mechanical properties of magnesium strips and low-carbon steel strips after processing on a roller straightening machine was carried out. The application of the strengthening process in 1 and 3 passes does not change the geometry of the strips. The yield strength of steel increases and the yield strength of magnesium decreases; at the same time, the yield plateau disappears on the tensile curve of steel samples, and a region similar to the easy slip stage in a single crystal appears on the tensile curve of magnesium samples after the elasticity stage. For an integral assessment of the effect of alternating deformation on the material and to determine its resistance to deformation, flow curves were constructed using the Nadai model.



Improvement of technological properties of metal alloys by nonmonotonic plastic deformation
Abstract
The article considers the task of improving the technological properties of a material in order to improve the ultimate deformation under the action of tensile normal stresses. The solution of this problem is based on the model of anisotropic hardening by G. Backhouse. The necessary ratios have been obtained to optimize the process of improving the technological properties of the material. In order to experimentally verify the obtained solution to the problem under consideration, experiments were performed on thin-walled tubes under conditions of loading them in the tension-torsion – tension cycle, confirming with an accuracy of less than 90% the possibility of using the proposed method of increasing critical deformation in production conditions.


