Metallurgist最新文献

With the aim of studying the occurrence of chromium reduction during argon-oxygen refining using boron oxide as a flux, thermodynamic modelling of the equilibrium interfacial distribution of chromium between slag of the oxide system CaO–SiO₂–(3–6%)B₂O₃–12%Cr₂O₃–3%Al₂O₃–8%MgO in the range of basicity 1.0–2.5 and metal depending on temperature, boron oxide content, and basicity is performed. Modelling results are shown as diagrams of the dependence of the equilibrium interphase distribution of chromium on slag composition at 1600 and 1700 °C. It is found that an increase in slag basicity from 1.0 to 2.5 at 1600 and 1700 °C leads in the range of boron oxide content studied to a decrease in the interfacial distribution coefficient of chromium from 60.0 · 10⁻³ to 1.5 · 10⁻³ and as a result an increase in the degree of chromium reduction from 91 to 99.5%. An increase in metal temperature and boron oxide content have little effect on chromium reduction. The influence of basicity of the slags studied on the chromium reduction process may be qualitatively explained from the perspective of phases formed within slags and thermodynamics of chromium reduction reactions with aluminum and silicon. Experimental studies confirm results of thermodynamic modeling.

In this study, existing and promising methods of processing fine fractions and dust of aspiration systems for the production of ferroalloys were analyzed. The technological properties of high-carbon ferrochrome screenings and dust of the ferrochrome crushing aspiration system of the Aktobe Ferroalloy Plant as raw materials for the production of low-carbon ferrochrome briquettes using the vacuum-thermal method were studied. The contents of basic and impurity elements, including gas-forming ones, were determined. The oxygen content in the dust reached 4.2 and 0.12% in the screening. The average size of aspiration dust particles was 9.6 μm, whereas that of the ferrochrome screenings was 1.44 mm. In the dust and screening samples, the main phase was Cr₇C₃, and graphite was present in the dust sample. During thermal analysis, the dust sample completely melted at 1453 °C, and a liquid phase was not observed when ferrochrome was heated. At 1340 °C, the formation of iron silicide was noted. With increasing temperature, the concentrations of carbon and chromium carbide decreased. From thermodynamic calculations, recommendations were given on the parameters of vacuum-thermal decarburization of high-carbon ferrochrome. The results of preliminary experiments confirmed the possibility of removing carbon from screenings and aspiration dust. From samples containing 9.04–9.11% carbon, ferrochrome with a content of 0.10% carbon could be obtained. At the next stage of our work, we plan to work out in detail the parameters affecting the vacuum-heat treatment of ferrochrome. We assume that ferrochrome with a carbon content of 0.00x% can be obtained.

An analysis of the operation of the piercing mill revealed the need to upgrade the mechatronic rolls positioning system and to introduce an intelligent system to improve the quality of rolled products. The main problem is the formation of defects at the ends of the shells during rolling on a piercing mill. The excess material must be cut off and recycled because more raw materials than required are used for rolling one billet. To eliminate this problem, it is necessary to change the preload of the workpiece during rolling, thereby forming a profile that reduces the undesirable changes at the ends of rolled pipes. The mill currently has foreign equipment which is difficult to purchase. Such difficulties may lead to downtime. Moreover, the unit operates only in manual or semi-automatic mode. The possibility of replacing equipment with domestic analogs is considered. A visualization and control program has been developed. To determine the position of the workpiece in the mill and change the preload of the shell in automatic mode, a neural-network control system has been developed.

As part of the development of critical technologies, it is necessary to search for alternative replacement of components in the compositions of aluminum ligatures, including known modifying additives of scandium and yttrium with other rare-earth and rare elements. Aluminum ligatures with rare-earth metals are widely considered in many scientific papers, but the research on the production of Al-Yb ligatures is limited. In this paper, the authors describe the results of studying the production of ligatures of the aluminum-ytterbium system from ytterbium oxide by aluminothermic reduction, containing nanoscale Al₃Yb intermetallic compounds and eutectics in their structure. Serving as crystallization centers, the optimal-size particles of intermetallic compounds provide uniform fine-grained structure in aluminum alloy castings. The relationship has been obtained that enables the maximum transition of ytterbium into the alloy depending on the quantitative and qualitative composition of the reaction mixture and various melting process parameters. The conducted studies have shown that ligatures obtained by aluminothermic reduction of ytterbium oxide with the addition of 5 to 15 wt. % Mg to the reaction mixture have the highest characteristic of ytterbium transition into the ligature.

Magnesium foam is a promising material in industry and medicine due to its low density, high damping properties, ability to absorb acoustic and electromagnetic vibrations, and biocompatibility with the human body. The methods developed for producing products from porous magnesium by filtering the liquid melt through soluble granules ensure the production of porous magnesium with a pore size of at least 4 mm. To reduce the pore size by increasing the fluidity and fillability of the granular filling during the production of porous magnesium, vibration treatment of the melt during pouring has been proposed. The conducted studies have shown that vibration treatment allows increasing the fluidity of the Mg90 magnesium melt. In addition, a refinement of the magnesium structure and an increase in hardness are observed. Vibration treatment during the pouring and forming of porous magnesium contributes to an increase in the depth of impregnation of the granular filling and creates conditions for producing products from porous magnesium with a pore size of up to 2 mm, a density of 0.55–0.75 g/cm³, and a porosity of 57–68%.

Based upon calculated data compositions of experimental aluminum alloys, which are characterized by the lowest tendency towards hot brittleness during casting, are selected. Sheets 2.5 mm thick are obtained from ingots of experimental alloys by hot rolling. It is shown that weldability of the Al–1Ca–5.5Zn–1.5Mg–0.5Mn alloy is at the level of that for serial alloy 1915. Analysis of the obtained data shows that cracking characteristics of the Al–2Ca–2.5Mg–0.4Mn alloy (alloy 2) (specimen cracking coefficient and critical deformation rate) are at a level corresponding to AMg3 alloy. The alloys studied with appropriate surface preparation are not prone to pore formation during fusion welding. Mechanical properties of joints of the alloys studied during argon-arc and plasma welding are determined.

WAAM technology (Wire + Arc Additive Manufacture) is a new method of additive manufacturing using wire as a construction material. The high productivity of the process, the ability to construct large-sized products without the need to use a controlled atmosphere chamber, and the low cost of equipment and construction materials allow using the WAAM technology to built products of simple and medium complexity with the highest economic efficiency. However, WAAM technologies in MIG-Pulse/CMT surfacing processes have a number of disadvantages, such as significant size of the heat-affected zone (HAZ) and large sizes of the build-up layer, which leads to undesirable temperature gradients and the accumulation of residual stresses. A further way to improve WAAM technology is to use metal-cored wires. For the research, metal-cored wire Cr20Mn5Ni4Mo2.5Cu3N0.3 Ø 1.6 mm was developed. It has been established that the use of metal-cored wire allows producing a defect-free surfaced metal with an austenite-ferritic structure (δF ≈ 1–3%), which has high strength and plastic characteristics (σ_B = 810 MPa, σ_0,2 = 500 MPa, δ = 40%). The yield strength of the developed composition is more than 2 times higher than that of the widespread austenitic steel of the Kh18N10T type (σ_0,2 = 206 MPa). Further research will be aimed at improving the impact strength of the surfaced cast metal by optimizing the composition of the metal-cored wire.

The article presents a structure of the algorithm and mathematical and software systems. The general characteristics of the algorithm for determining heat losses in the hearth of a blast furnace based on the use of the heat balance of the lower zone are presented. External heat losses in the process of melting occurring through the tuyere belt, barrel, and bosh, are determined by the difference between the input and output components of the zonal heat balance for the lower part of heat transfer. The determination of heat losses by the heat balance in the lower heat transfer part allows their value to be estimated according to the current information about the operation of the furnace under specific raw materials and operating parameters. The information support of the system is presented, the software architecture is described, the characteristics of the software modules are given, and fragments of its work are illustrated. The information modeling system is distinguished by taking into account the basic physical and chemical laws of the processes of the control object, the principles of system analysis, and the use of modern principles for the development and construction of mathematical models and software. Heat loss control is necessary to assess the condition of the blast furnace refractory lining and rational gas distribution, as well as to adjust the coke rate.

The possibility of representing the process of temper rolling for a galvanized cold-rolled strip as a simultaneous deformation of a binary zinc-steel system is demonstrated. It is confirmed that the simultaneous plastic deformation of the components of the galvanized strip during its temper rolling occurs when the critical thickness of zinc is achieved. The process of reproducing the microgeometry of the textured surface of the roll on a galvanized cold-rolled strip during its temper rolling is considered the process of filling the micro-cavities of the roll with the material in contact with it. A mathematical dependence is obtained for calculating the reproducibility ratio of the parameters of the textured surface on a cold roll on a galvanized cold-rolled strip, depending on the thickness and mechanical properties of the galvanized coating and steel strip, equipment characteristics, modes, and conditions of its temper rolling, as well as on the roughness parameters S, Ra, and P_c of the roll surface. A comparative assessment of the influence of the technological parameters of temper rolling on the reproduction ratio of the microgeometry of the roll surface on a galvanized cold-rolled strip is provided.

An automated control system for the coiler mandrel is developed. The causes of emergency situations are identified not only in the industrial conditions, but also from data obtained by reviewing the relevant literature and solving similar problems at other companies. A change in the tension of the strip due to the instability or malfunction of the coiler drive is revealed. This causes degradation in the quality of the rolled strip, its thickness variation, or even breakage. In addition, the installed system does not have a wide range of setpoints, thereby hindering the expansion of the range of rolled steel. One of the main causes of such problems is the outdated coiler mandrel motor and the lack of a proper control system. The developed automated control system is described mathematically. A torque compensation unit maintaining the required level of strip tension is designed. Matlab Simulink software is used to generate a model of an automated control system for the coiler mandrel and to analyze the strip tension and the associated electrical-drive parameters (speed, current, magnetic flux), which confirms the absence of jerks during coiling. The economic benefits of the implementation of this project are calculated. The payback period is about a year.