Abdrakhman Naizabekov

This study investigates the stressed state of metal under conditions of asymmetric limit influence on the deformation center under complex inhomogeneous loading. The task addressed is control over additional interaction under conditions of asymmetric force loading at a single deformation center. This indicates the possibility of managing the plastic shape change process. The control factor of influence is the additional influence on the plastic deformation center. Based on experimental and theoretical studies, it has been shown that the additional influence on the deformation center can be implemented through various control factors, in particular through the factor of non-uniformity of deformation along the deformation center height. The possibility of using this deformation-geometric factor as a control influence in plastic treatment processes has been established and substantiated. In plastic deformation processes, a combination of different types of loading is possible. If one of them is smaller in magnitude than the principal one, such a load is interpreted as additional. According to the research results reported in this work, the factor of deformation non-uniformity has been justified as a control factor. A feature of the results is that the presence of the non-uniformity factor changes the force load parameters in the boundary zones of the deformation center. In this case, shear strains are generated at the site itself, which significantly changes the kinematics of the metal flow and causes the effects of plastic shape change associated with a decrease in the rolling force. Features of plastic interaction and effects of plastic shape change have been identified, the main indicator of which is a decrease in the rolling force under conditions of additional control influence. This could affect the accuracy of rolling, process productivity, grain size, and wear of work rolls

The purpose of this work was to study the influence of two different schemes of deformation of workpieces in a radial-shear rolling mill on the microstructure evolution of steel workpieces. A direct deformation scheme was considered, which provided for the repeated rolling of the workpiece in the second pass, and a reversible deformation scheme, in which the mill rolls rotated in the opposite direction during the second pass of deformation, and the workpiece was captured at the exit of the rolls. These studies were conducted both by computer simulation and by conducting a physical experiment. The results show that the use of a reversible deformation scheme makes it possible to better work out the axial zone of the resulting rods, compared with using a direct deformation scheme. At the same time, the direct deformation scheme allows for more intensive work on the surface area of the rods. Due to this, with a direct deformation scheme, a gradient structure with fine grains on the surface and elongated grains in the axial zone is formed in the cross section of the deformed bar, and with reverse rolling, conditions are provided for obtaining a more homogeneous structure.

Based on experimental studies, a model of the control effect on the plastic deformation process under boundary asymmetric loading conditions has been developed. The regulating factor of plastic deformation unevenness δ, which determines the stress–strain state of the entire deformation zone and the boundary conditions, is presented. The boundary conditions, determined by additional compressive and tensile stresses along the height, generate shear stresses and specific loading regimes at the edges and within the deformation zone itself. The confirmed reduction in interaction, which coincides with the effect of plastic deformation occurring under conditions of force unevenness, is one of the criteria for the controlling effect. A distinctive feature of this approach is the recognition and proof of the existence of a controlling additional effect under conditions of complex force and deformation loading. Theoretical and experimental studies have revealed such effects under various loading conditions. Based on a closed-form problem in plasticity theory and the method of argument functions of a complex variable, a mathematical model of the control process exerted by the metal’s plastic flow zone has been developed. A key feature of the solution to this theoretical problem was the consideration of the interaction between zones under different force loads, represented by a finite-difference scheme in the mathematical model. The decisive influence of deformation unevenness from the working rolls on the force and deformation parameters of the process was demonstrated, with the deformation unevenness factor δ serving as a quantitative measure of this influence. The result obtained through theoretical justification was confirmed by numerical simulation and a comparison of calculated data with experimental data, ensuring the reliability of the result.

Modern materials science is focused on the development of steels with a range of performance characteristics, including high strength, wear resistance, corrosion resistance, and long-term performance in various conditions. Special attention is paid to the control of the microstructure of steels at the crystallization stage, which allows for the improvement of metal properties without significantly increasing the cost of the manufacturing process. One of the promising methods of microstructural engineering is the modification of steels with dispersed particles of refractory compounds, such as titanium carbide (TiC), zirconium carbide (ZrC), and tungsten carbide (WC). However, the processes of dissolution, dissociation, and interaction of such ceramic particles with the metal melt, as well as their influence on the formation of the microstructure and properties under the conditions of non-equilibrium crystallization, which is typical for centrifugal casting, are not sufficiently studied for austenitic stainless steels. In this work, the influence of dispersed carbide particles of TiC, ZrC, and WC, which are introduced into the melt of austenitic stainless steel (Cr ≈ 18%, Ni ≈ 10%) during centrifugal casting, on the redistribution of alloying elements, the formation of the microstructure, and the mechanical properties of the material is investigated. Special attention is paid to the kinetic nature of the dissolution and interaction of the carbides with the melt, as well as the directional distribution of elements across the cross-section of the billets. The study includes the analysis of the distribution of Ti, W, and Zr across the cross-section of the centrifugally cast billets, the study of the microstructure and phase composition of the inclusions using SEM/EDS, and mechanical testing. It is found that the implementation of dispersion hardening leads to an increase in the tensile strength by up to ~22% compared to the initial alloy (from 496 to 612 MPa), while the impact strength decreases by 5–25% (from 110 to 82 J/cm²) depending on the type and quantity of the introduced particles. The analysis of microhardness shows the presence of a gradient of local properties across the cross-section of the centrifugally cast billets, with microhardness values ranging from ~110 to 195 HV0.5. For the modified samples, the relative difference between the inner and outer zones is ~5–20%, reflecting the combined effect of non-equilibrium solidification, redistribution of alloying elements, formation and spatial distribution of secondary phases, and local structural heterogeneity. These results confirm the possibility of controlling the distribution of properties within a single billet.

The principal way to improve the mechanical and operational properties of steel is to adjust its chemical composition or to grind the metal structure. An alternative to the use of expensive alloying elements to improve the mechanical and operational properties of steel can be the dispersed hardening of steel with hard refractory fine particles of carbides, oxides, nitrides. This work, which was carried out within the framework of grant № AP23485709, funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan, is devoted to the study of the possibility of introducing dispersed boron carbide particles into the melt of austenitic steel 12X18H10T during centrifugal casting. At the first stage of the research, the interaction of dispersed particles of boron carbide and steel was simulated using the FactSage software package. The simulation showed that boron carbide particles will interact with the metal melt of austenitic steel 12X18H10T, which can lead to their complete dissociation. At the next stage of crystallization, the formation of carbide phases based on titanium carbide with a HCC structure, as well as a carbide phase based on chromium carbide with the formula M23C, will begin, starting at a temperature of 1250°C. When the temperature decreases to 1050°C, the separation of boride phases based on chromium begins in the system under consideration. The experiments and metallographic analysis carried out at the second stage of the research confirmed the results of thermodynamic modeling. The introduced boron carbide particles completely dissociate when interacting with a metal melt. The carbon contained in the composition of boron carbide and in the composition of the initial melt contributes to the formation of carbide and carbon-nitride phases based on titanium.

Radial-shear rolling (RSR) technology is the most promising and effective way to produce various high-quality long-length metal products from ferrous and non-ferrous metals and alloys, including those with a gradient ultrafine-grained structure. RSR scheme has one main difference from the well-known cross–screw rolling scheme - an increased feed angle α = 18°-20°. In this case, the rolling angle β remains in the range from 5 to 7°. Based on this scheme (i.e., the RSR scheme), a number of radial-shear rolling mills were developed and put into small-scale production. In this paper, we review our team’s experience in using the radial-shear rolling method to improve the structure and properties of various ferrous and non-ferrous metals and alloys. The review of scientific publications of our team in this area given in this article indicates the prospects of using RSR technology to produce high-quality metal products with a given level of properties.This study was supported by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26100119).

This study’s object is the stressed state of the plastic deformation site under conditions of load asymmetry when metal is gripped by rolls, under the determining modes of process stability. The task addressed is the implementation of shape change at the rolling process stability threshold related to a decreased force load under the increased strain impact. A physical and mathematical model of a flat rolling theory problem has been built under conditions of multi-parameter factors affecting the gripping capacity of rolls and the stability of rolling process. The plasticity theory problem was solved analytically using the method of argument of a function of a complex variable. The solution to the plane problem is shown, using the asymmetry of the process, the counter-directed flow of metal. The nonlinearity of the plasticity theory problem was taken into account. Based on the mathematical model, a new force factor was identified and investigated: the force stretching factor from the lagging zone. A new single-zone deformation mode with minimum process stability was identified. The process was investigated under conditions of multiparameter influence on rolls gripping ability and its stability. The zones of reachability were established for a deformation focus shape factor within the range of 5.00...15.00. The mode of partial suppression of the zeroing factors of the metal stressed state was investigated under conditions of multi-parameter influence on the gripping ability of the rolls and the stability of the process. Stability indicators of transient modes were determined: at α = 0.077, the ratio f/α = 1.10…1.95; at α = 0.129, the ratio f/α = 1.19…1.95; at α = 0.168, the ratio f/α = 1.28…1.95. This study’s results make it possible to solve technological problem related to the development of rolling schemes when the gripping force of friction and the pushing force of normal pressure arise during the forming process

The model explicitly incorporates boundary conditions that account for the complex interplay between sections experiencing varying degrees of reduction. This interaction significantly influences the overall deformation behavior and force loading. The control effect is associated with boundary conditions determined by the unevenness of the compression, which have certain quantitative and qualitative characteristics. These include additional loading, which is less than the main load, which implements the process of plastic deformation, and the ratio of control loads from the entrance and exit of the deformation site. According to this criterion, it follows from experimental data that the controlling effect on the plastic deformation site occurs with a ratio of additional and main loading in the range of 0.2–0.8. The next criterion is the coefficient of support, which determines the area of asymmetry of the force load and is in the range of 2.00–4.155. Furthermore, the criterion of the regulating force ratio at the boundaries of the deformation center forming a longitudinal plastic shear is within the limits of 2.2–2.5 forces and 1.3–1.4 moments of these forces. In this state, stresses and deformations of the plastic medium are able to realize the effects of plastic shaping. The force effect reduces with an increase in the unevenness of the deformation. This is due to a change in height of the longitudinal interaction of the disparate sections of the strip. There is an appearance of a new quality of loading—longitudinal plastic shear along the deformation site. The unbalanced additional force action at the entrance of the deformation source is balanced by the force source of deformation, determined by the appearance of a functional shift in the model of the stress state of the metal. The developed theory, using the generalized method of an argument of functions of a complex variable, allows us to characterize the functional shift in the deformation site using invariant Cauchy–Riemann relations and Laplace differential equations. Furthermore, the model allows for the investigation of material properties such as the yield strength and strain hardening, influencing the size and characteristics of the identified limit state zone. Future research will focus on extending the model to incorporate more complex material behaviors, including viscoelastic effects, and to account for dynamic loading conditions, more accurately reflecting real-world milling processes. The detailed understanding gained from this model offers significant potential for optimizing mill roll designs and processes for enhanced efficiency and reduced energy consumption.

This research developed a complex physical and mathematical model of the flat rolling theory problem. This model takes into account the influence of many parameters affecting the roll’s gripping capacity and the overall stability of the entire rolling process. It is important to emphasize that the method of the argument of functions of a complex variable does not rely on simplifying assumptions commonly associated with: the linearized theory of plasticity; or the decoupled solution of stress and strain fields. Furthermore, it does not utilize the rigid-plastic material model. Within this method, solutions are developed based on the complete formulation of the system of equations in terms of stresses and strains, incorporating constitutive relations, thermal effects, and boundary conditions that define a well-posed problem in the theory of plasticity. The presented applied problem is closed in nature, yet it accounts for the effects of mechanical loading and satisfies the system of equation. For this purpose, such factors as roll geometry, physical and mechanical properties of the rolled metal (including its fluidity, hardness, plasticity, and structure heterogeneity), rolling speed, metal temperature, roll lubrication, and many other parameters that can influence the process have been taken into account. Based on the developed mathematical model, a new, previously undescribed force factor significantly affecting the capture of metal by rolls and the stability of the rolling process was identified and investigated in detail. This factor is associated with force stretching of metal in the lagging zone—the area behind the rolls, where the metal has already left the deformation zone, but continues to experience residual stress. It was shown that this stretching, depending on the process parameters, can both contribute to the rolling stability and, on the contrary, destabilize it, causing oscillations and non-uniformity of deformation. The qualitative indicators of transient regime stability have been determined for various values of the parameter α. Specifically, for α = 0.077, the ratio f/α ranges from 1.10 to 1.95; for α = 0.129, the ratio f/α ranges from 1.19 to 1.95; and for α = 0.168, the ratio f/α ranges from 1.28 to 1.95.

This paper is devoted to the study of the influence of a combined technology, including both preheat treatment and deformation on a radial-shear rolling mill, on changes in the mechanical properties of M1 grade copper. The conducted studies have shown that after preliminary heat treatment, namely quenching at a temperature 500°C, and subsequent deformation of billets at temperatures of 20 and 200°C on a radial-shear rolling mill, an increase in the strength properties of copper is observed with a decrease in its plastic properties within the normal range. Also, according to the results of the conducted studies, it was found that the crosssection of the obtained copper bars shows a spread of microhardness values, which fully correlates with the data on the formation of areas with different microstructures after radial shear rolling in this cross-section.