Metallurgist最新文献

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.

We perform structural investigations of a molybdenum-based cermet material obtained by the method of selective electron-beam melting. The initial material is an alloy of the Mo–Si–B system alloyed with a reinforcing component in the form of an Al₂O₃–Y₂O₃–ZrO₂ oxide composition. It is shown that, in the process of selective electron-beam melting of spheroidized cermet particles of the alloy of Mo–Si–B system in the optimal technological mode of synthesis, we observe melting both of the molybdenum matrix of the alloy and of the reinforcing particles contained in the original granules. As a result, in the course of crystallization of the melt with formation of a cellular structure on the boundaries of cells, we observe the appearance of finely divided oxide particles 1–5 μm in size, which are also composite particles. On the boundaries of cells and inside oxide inclusions, we reveal the elevated content of silicon as compared to that in the body of cells, which enables us to conclude that the processes of diffusion of this element occur in the analyzed material. At the same time, in the vicinity of the contour of samples of synthesized material, we detect the formation of a structure, which inherits, to a certain extent, the structure of the initial spheroidized granules.

An analysis of new legislative documents on the management, methods, and technologies for assessing environmental risks was performed. The risk assessment algorithm was applied to the foundry shop of a metallurgical enterprise (Proizvodstvennaya Kompaniya) in the city of Irkutsk. The technological process of casting and forming steel products was investigated with a detailed analysis of emissions into the environment for each technological stage. The measures currently used by the enterprise to reduce its negative impact are discussed. When identifying the sources of hazards in the foundry, numerous violations of environmental legislation were identified. A register of environmental hazards with a ranking of consequences was compiled, which showed that the most severe hazard to the ecosystem would occur in the event of a global fire at the foundry shop with a possibly fatal outcome. The scenario of an electric arc furnace accident with the release of pollutants into the atmosphere was calculated as the most negative event. To assess the risks of possible hypothetical accidents, the event tree analysis, failure mode and effects analysis, and failure mode, effects, and criticality analysis methods, which are semiquantitative and suitable for primary risk assessment, were used. The calculation of the probability and criticality of failures of electric arc furnace elements showed that, if the cooling system fails, then the furnace will explode and the foundry shop will catch fire, threatening the lives of workers and emitting a large amount of pollutants into the atmosphere. Equipment modernization was proposed as corrective measures taking into account the best available technologies.

This article discusses the option of upgrading an ore-thermal furnace to produce technical silicon by installing strain gage sensors with signal converters and a rangefinder in the electrode lifting system. This upgrade will enable the reception of real-time data on changes in mass (carbon monoxide) or electrode breakage and the position of the working end of the electrode. The latter parameter is associated with the position of the reaction zone in the furnace, which directly affects the specific amount of electricity consumption, the temperature and volume of silicon leaving the furnace, and heat losses and dust removal with exhaust gases.

The upgrade will increase the observability of the control object, which will improve the quality of control of the technological process of carbothermic silicon reduction.

This work extends the boundaries of a new technology for the complex processing of dust obtained from melting scrap metal in electric arc furnaces at a factory in Kazakhstan by extracting zinc and lead into commercial products. Comprehensive studies of the elemental and phase compositions of dust conducted using a JED-2300 scanning electron microscope showed high contents of zinc (more than 30%), lead (approximately 5%), and iron. A considerable part of the iron in the dust (up to 35%) is represented as magnetite. Because of the lack of rational processing technology, a large amount of dust has accumulated on the plant territory, which requires a solution for its disposal with complex extraction of precious metals.

The general concept of the technology under development is based on an approach that ensures the disposal of multicomponent ferrous metallurgy dust to obtain a wide range of commodity products with high added value. At the same time, the high content of iron present as magnetite demonstrates the effectiveness of isolating iron as an iron-containing commercial product at the beginning of the technological scheme.

This paper shows the fundamental possibility of separating iron from dust from the scrap metal melting in electric arc furnaces by magnetic separation. According to comprehensive studies, including the study of the material composition of the initial dust and magnetic separation products, magnetic dust separation produced an iron-containing product with a high (up to 68%) iron content. The residual minimum limit of the iron content in the nonmagnetic fraction in the form of magnetite has been established as 0.58%. Further processing of such material will considerably simplify the technology, reduce material costs, and improve product quality.

This article presents an overview of the technology employed in the production of special types of coke obtained from non-sintering coals sourced from Kazakhstan. The microstructure of special types of coke is elucidated, and the effect of the heating rate on their microstructure and properties essential for use as a reducing agent in electrothermal processes for the production of technical silicon metal is studied.