Metallurgist最新文献

This paper presents the results of the testing of the technology for processing liquid slags of a precious metal shop in a rotary-type unit. The main feature of the unit is its ability to process metallurgical slag in a liquid state to obtain a product with a wide range of properties and purposes. The technical characteristics of the pilot plant are given. The peculiarities of cooling high-temperature slag melts on moving metal bodies placed on grates forming a cylindrical surface are presented. Metal bodies (spheres) can move along the grate surface and simultaneously extract the heat of the slag melt. To control the cooling process, the design of the unit provides systems for supplying and distributing water and removing a combined-cycle gas mixture. The grate surface in the form of a rotor is covered with a heatproof and soundproof casing, which is connected to a steam–gas mixture removal system. The melt cooled in the rotor cavity enters the trough conveyor. The conveyor is also covered with a casing and connected to the steam–gas mixture removal system. Examples of different modes of slag melt cooling in a rotary-type unit are presented. A variant of discharging cooled slag directly under the rotor into a special box equipped with a sewage drainage system is tested. Satisfactory results can be achieved in obtaining crushed stone and crushed stone–sand mixtures with the required properties directly from slag melts.

In recent years, lightning protection cables with integrated optical module are used fairly extensively. These cables actually have the form of a cable made of several layers of steel wires with corrosion-resistant coating and a tubular case made either of aluminum or of stainless steel (central or in a whip) filled with a hydrophobic gel and optical fibers. Circular plastic compression in the process of production of lightning protection cable with integrated optical module enables us to improve the electric contacts of wires in and between the layers and increase both the resistance to the lightning discharge impulse and mechanical strength. For the incorrectly chosen geometric parameters of wires in the first and second layers, circular plastic compression may lead to a significant deformation of the optical module and, as a result, to the unacceptable elevation of the coefficient of attenuation of the transmitted signal. By the method of computer simulation, we determine the value of guaranteed gap between the inner layer of the lightning protection cable with integrated optical module and the central tube guaranteeing the decrease in the level of deformation of the outer shell of the optical module down to admissible values. The possibility of formation of lateral contacts between the wires of the first layer contributing to a decrease in the radial component of pressure transmitted to the surface of the module is demonstrated for the optimized design of the cable. The accumulated results of computer simulation can be used for the optimization of the design and geometric parameters and the level of strand compression required to minimize the deformation of the outer shell of central tube of the integrated optical module of the lightning protection cable.

In this work, the main electrochemical characteristics of the zinc alloy TsAMg4.5‑2 with scandium, yttrium, and lanthanum in a NaCl electrolyte medium were determined using the potentiostatic method in the potentiodynamic mode at a potential sweep rate of 2 mV/s. Studies on the corrosion–electrochemical behavior of a zinc alloy showed that the potentials of free corrosion, pitting formation, and repassivation of alloys shifted to a positive region with an increase in the concentration of a rare-earth metal. Meanwhile, alloys doped with small additives of specified elements (0.1–0.5 wt.%) were characterized by increased corrosion resistance. The decrease in corrosion rate was associated with the passivation process of alloys. With an increase in the concentration of chloride ions in the NaCl electrolyte, the potentials of corrosion and pitting formation shifted to the negative region, whereas the corrosion rate of the alloys increased.

The results of studies on the influence of the modes of shielded arc welding with a non-consumable electrode on the mechanical properties of parts manufactured from EK-61 powder alloy by direct laser deposition are presented. The results of metallographic studies of the weld and heat-affected zone are described. The possibility of obtaining high-quality welds using shielded arc welding of such products is shown. The influence of the number of passes on the quality of the weld is noted.

The sphere packing theory is used to study the influence of the particle-size distribution in the material on the porosity of briquettes and pellets, and the fractional composition of agglomerated products on the porosity of layers of such charge components. Understanding how the porosity of agglomerates varies with the particle-size distribution in the starting material, it is possible to optimize the metallurgical properties of briquette and pellets. The porosity of a layer of such products largely determines their behavior during both reduction (in blast furnaces, ore-thermal furnaces, and direct-reduction reactors) and pellet firing. The results obtained made it possible to identify for the first time the local extrema in the porosity of agglomerates and the porosity of a layer of pellets (briquettes). The developed heuristic approach can be used for optimizing the composition of mixtures for agglomeration, increasing the efficiency of pellet firing, and achieving high degrees of metallization in reducing an agglomerated charge. This approach accounts for the compressibility and shape irregularity of particles in both starting mixture and agglomerated products.

The objective of this study is to determine the optimal composition of slag formed in the ladle furnace unit with maximum desulfurizing properties. A method of calculating the refining properties of slag that takes into account the ionic nature of oxide melts is proposed. Based on the revealed regularities, slag compositions are selected depending on the technological operation of deoxidizing/alloying. As a result of the implemented measures, sulfur removal performance in the ladle furnace unit was improved, and the costs of slag-forming materials were reduced.

The physical mechanism of self-organization of a multilayer nanolaminated coating based upon non-equilibrium (TiAlCrSiY)N/(TiAlCr)N nitride on a cutting tool during high-speed (600 m/min.) dry cutting of N13 steel is established. Using a set of modern surface analysis methods coating degradation and tribo-oxidation are studied within the running-in and steady stages of wear. It is shown that during cutting, amorphous-nanocrystalline films of oxides similar to Cr₂O₃, TiO₂, Al₂O₃ (sapphire) and Al₂O₃ · 2 (SiO₂) (mullite) are formed within a wear crater. Using computer calculations by a finite element method, heat transfer is considered in the cutting zone during formation of protective tribo-oxides. It is found that among all tribo-oxides, mullite has the best thermal barrier properties. Oxidation is the main adaptation mechanism of a cutting tool under extreme mechanical and thermal shock during high-speed cutting. The topography of chip contact surface is studied at various cutting stages, which makes it possible to establish a change in plastic deformation mechanisms of treated metal and friction cutting modes. Quantum chemical calculations of the electron structure of mullite show the highest degree of its electron polarization and explain the radical drop in friction coefficient during film formation upon a wear surface. In this case, mullite acts as a solid lubricant.

The causes of the formation of bumps on metallographic specimens of sheets and strips subject to inspection are established by analyzing the components of Kovar alloy (trademarked name of Fe29%Ni18%Co precision alloy; named 29NK-VI in Russia) and identifying possible deviations from its manufacturing process, starting from the preparation of the initial melt. It was found out that the formation of bumps is a manifestation of leading diffusion of some alloy components into others, mainly cobalt into nickel. Such a phenomenon may occur in case of significant chemical inhomogeneity of the metallic material caused by the segregation of the components of its initial melt according to their magnetic susceptibility and the refusal to homogenize the resulting ingot.

It is argued that bumps on specimens should be considered as a rejection criterion for a material intended for the manufacture of precision parts of vacuum electronic devices, as they are indicative of its unbalanced composition. The residual diffusion phenomena contribute to the change in the phase state of the material, followed by embrittlement, change in precise dimensions, and loss of vacuum in parts of vacuum electronic devices. It is assumed that residual diffusion is one of the causes of the γ→α phase transformation in Kovar at low temperatures.

Two-high screw rolling of stainless-steel billets at feed angles of 6, 12, 18, and 24° was numerically simulated. It was established that increasing the feed angle of the rolls decreases the magnitude and inhomogeneity of the shear strains in the billet cross-section. With increase in the feed angle, the difference between the total velocities zone on the surface and at the center of the billet in the deformation decreases by 57%, the length of the geometric deformation zone decreases, and the length of the actual deformation zone increases by 16%.

An experimental investigation was carried out to assess the impact of manufacturing technologies on the fracture mechanisms and fatigue mechanical properties of drill pipe N (in its normalized state) and pipe U (following improvement) under cyclic loads. Two strength groups of drill pipe, N and U, were subjected to study. The presence of a highly tempered fine-dispersed structure in the material of pipe U, in comparison to the ferrite-perlite structure of the material of pipe N, provides enhanced resistance to fatigue crack initiation. This is confirmed by the values of the endurance limits, which are 503 MPa for pipe U and 294 MPa for pipe N. The fatigue tests carried out in the air revealed an inflection in the fatigue curves. For the metal of drill pipe N, the inflection corresponds to a value of 343 MPa, while for the metal of pipe U, it corresponds to a value of 522 MPa. Such inflection is associated with the formation of a barrier in the form of a hardened surface layer that arises during testing.