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Vol 49, No 2 (2019)
- Year: 2019
- Articles: 13
- URL: https://journals.rcsi.science/0967-0912/issue/view/11232
Article
Influence of Electrode Rotation in Electroslag Remelting on the Anisotropy of Ingot Properties
Abstract
In the analysis of electroslag remelting, attention is focused here on how rotation of the consumable electrode affects the physicomechanical properties of the ingot (billet) produced. In electroslag remelting with rotation of the consumable electrode around its axis, an ascending heat flux is formed in the slag bath. That improves the hydrodynamic conditions in the mold in terms of heat utilization. With rotation of the consumable electrode, centrifugal forces act on the film of liquid metal formed at the end of the electrode, resulting in radial flow of the metal droplets. The droplets subsequently break away from the electrode perimeter. Thus, the droplets of electrode metal enter the metal bath closer to the mold wall. That ensures a more uniform temperature front in the bath. With decrease in the temperature gradient over the bath cross section, a flatter solidification front is obtained. Such electroslag remelting with rotation of the consumable electrode will affect the physicomechanical properties of the ingot (billet) produced. Remelting trials are conducted to establish the resulting influence on the metal properties. Data are presented for the experimental electroslag remelting of AISI420 streel electrodes in an A-550 system, using different methods. The experimental data show how rotation of the consumable electrode affects the remelting conditions, the solidification of the ingot, and its physicomechanical properties. Its influence on the ingot properties is of particular interest: data regarding the microhardness, density, and size of the dendritic cell in the experimental samples are analyzed. It is found that, in electroslag remelting with rotation of the consumable electrode, the microhardness is more uniform in the transverse direction. In addition, with rotation of the consumable electrode, the dendritic cell is smaller, and the ingot density is higher, than in the classical technology without electrode rotation.
77-81
Improving Induction Crucible Furnaces
Abstract
The main deficiencies of existing induction crucible furnaces are associated with elevated wall thickness of the lined crucible, the tubular copper single-layer inductor (with internal cooling by conditioned water), and the absence or presence of surrounding vertical I-shaped composite metal rods, forming a discrete ferromagnetic screen. The first deficiency is that much of the working electromagnetic flux Φwo is wasted, since it passes along the crucible lining, which is not electrically conducting, rather than along the furnace charge. Only 38.5–57.0% of Φwo is utilized. The second deficiency is associated with the high cost and laboriousness of manufacturing the inductor turns from special copper pipe, which vibrates at double frequency. That creates noise and weakens the furnace structure. Such inductors are characterized by low electrical efficiency and high costs of preparation and cooling of the conditioned water in systems of area several times greater than the furnace itself. The consequence of the third deficiency is that much of the electromagnetic scattering flux Φsc is not involved in heating the batch and the melt but instead heats the electrically conducting elements of the furnace, including the magnetic rods that surround the inductor. Because of the poor utilization of the total flux Φ generated by the inductor, the efficiency is decreased practically to 19–30%, while the power factor falls to 0.03–0.10, with increase in the energy consumption. To minimize or eliminate the deficiencies, three modifications are proposed: decrease in the sleeve’s wall thickness, with simultaneous strengthening by installing a cylindrical shell between the crucible and the inductor; introduction of a magnetic ring around the inductor; and the use of a single-wire or multicore inductor, instead of a tubular inductor. The combination of a cylindrical shell, a magnetic ring, and upper and lower housing plates permits the formation of a closed annular cavity where the inductor may be placed, with cooling of the inductor and the magnetic ring by circulating fluid. On the basis of research, a new design of an induction crucible furnace with a wire inductor and a composite magnetic ring (magnetic core) has been developed at Polzunov Altai State Technical University, tested, and patented. In experiments, the efficiency of the proposed structural elements is confirmed, indicating that the design merits further study.
82-86
Influence of B2O3 and Basicity of CaO–SiO2–B2O3–Al2O3 Slag on the Saturation Concentration of Magnesium Oxide
Abstract
The influence of boron oxide B2O3 and the basicity of CaO–SiO2–B2O3–Al2O3 slag on the saturation concentration of magnesium oxide MgO is studied by means of simplex experiment-design lattices. That permits the formulation of mathematical models describing the dependence of the specific property on the composition in the form of a continuous function. Synthetic slags corresponding in composition to the vertices of the given simplex are produced in graphite crucibles from preroasted analytically pure oxides. The slag compositions corresponding to the other points of the local simplex design are obtained by cross-mixing of the slags at the vertices. The experimental data provide the basis for mathematical models describing the influence of the slag composition on the saturation concentration of magnesium oxide MgO. The results of mathematical modeling are presented as a graph of the slag composition against the saturation concentration of magnesium oxide MgO. By analysis of the results, new information is obtained regarding the influence of the boron oxide and the basicity of CaO–SiO2–B2O3–Al2O3 slag on the saturation concentration of magnesium oxide MgO. It is found that, for slags formed in regions of basicity 2—3 with 1–3% B2O3, the saturation concentration of magnesium oxide MgO varies from 3 to 9%. Increase in the B2O3 content to 4% increases the saturation concentration of magnesium oxide MgO to 11–13%. Switching to slags of basicity 3–4 lowers the saturation concentration of magnesium oxide MgO to 2–5% with 1–3% B2O3 and to 7–9% with 3–4% B2O3 in the slag. Slag formation in the region of basicity 4–5 with 1–3% B2O3 does not significantly decrease the saturation concentration of magnesium oxide in the slag. In this basicity range, the saturation concentration of magnesium oxide MgO in the slag varies from 2 to 4% and hardly reaches 7% with increase in B2O3 content to 4%. In that case, the cost of the steel rises, on account of the increase in the consumption of lime and the material containing B2O3.
87-90
Determining the Fatigue Characteristics of Material on the Basis of Stress-Wave Emission
Abstract
Assessment of the fatigue of test samples on the basis of stress-wave emission is considered. Experiments are conducted on the basis of previously published material regarding the use of synergetically organized acoustic emission. Experimental data for various materials demonstrate that the acoustic-emission signal permits ongoing determination of mechanical characteristics and, in particular, the fatigue. The samples for fatigue tests are prepared from five grades of steel and also from BrAZh9-34 bronze. Five experiments are conducted for each metal. The experimental samples are subjected to loads in small increments. In each step, the emission signal is recorded, and the next series of dislocations is prepared for subsequent loading of the crystal surface and the emission of a stress wave. Thus, energetically prepared dislocations ensuring sufficient power for stable signal recorded are emitted. The experimental data obtained on the basis of the synergetically organized acoustic emission are compared with the fatigue limit of the material determined from empirical formulas in terms of the strength. According to the Fisher test, the experimental results are adequate at the 5% significance level. Assessment of the experimental data for the fatigue limit obtained from the acoustic-emission signal by means of the Cochran test indicates that the dispersion of the experimental measurements is uniform for all the materials considered. The conclusion is that determination of the fatigue limit of a material on the basis of synergetically organized acoustic emission yields real-time experimental data on the fatigue limit, with sufficient precision.
91-96
Influence of Pulsed Electric Current on the Motion of Spontaneous Plastic-Deformation Waves in Steel-Plate Extension
Abstract
Despite growing interest in the intensification of shape changes by means of current pulses, very limited experimental and theoretical information regarding plastic deformation is available, and the physics of plasticization in metals has not been adequately studied. That is delaying the application of promising techniques in practice. In studying electrically stimulated plastic deformation, it may be useful to regard plastic flow as a wave process. By infrared thermography and double-exposure speckle interferometry, the plastic deformation of low-carbon steel in the presence of pulsed electrical current is studied in the present work. Such treatment increases the velocity of the plasticity waves by 65%. Analysis shows that the velocity distribution corresponds to a impact-transition wave. At first, the velocity of the material is zero (motionless clamp), but on the right side of the graph the velocity of the material is equal to the extension rate specified by the test machine. When current pulses are applied, the distribution of displacement velocities is split at both the mobile and immobile ends of the sample. Thermal data show that a temperature gradient runs from the clamps to the center of the sample. That does not match the distribution of the displacement. In the initial treatment by powerful current pulses, the sample temperature reaches 351 K in the central region of the sample and 330 K at the clamps. In other words, the difference is 21 K. Subsequent treatment increases the temperature only slightly. According to literature data, such increase in temperature decreases the yield point by 10% for the given steel. That corresponds to the results of the present experiments. The present work confirms previous findings regarding the change in velocity of the slow wave on current transmission. The splitting of the velocity values at the mobile clamp has not previously been reported.
97-101
Synthesis of High-Nitrogen Steel by SHS Reduction with Aluminum
Abstract
High-nitrogen austenitic steel is characterized by high strength, plasticity, and corrosion resistance. However, its production by traditional methods (under high nitrogen pressure) calls for energy-intensive and complex equipment. In terms of energy conservation, a simpler alternative is the reduction of metal oxides by means of aluminum under nitrogen pressure. The present work is devoted to thermodynamic modeling of such reactions. High-nitrogen nickel-free stainless steels (of Cr–N and Cr–Mn–N type) with around 1% nitrogen are produced by the proposed method. The structure of the steel samples is investigated by X‑ray diffraction, metallography, and transmission electron microscopy; their mechanical properties are also determined. Thermodynamic analysis shows that the reduction processes are incomplete. In synthesis, the most important parameter is the ratio of the aluminum and oxygen concentrations in the batch. Correct selection of this ratio entails a compromise between the completeness of reduction of the oxides, the content of aluminum and oxygen in the steel (the degree of reduction), and its contamination with aluminum nitride. Cast ingots of Cr–N steel are characterized by the structure of nitrogen-containing pearlite (ferrite–nitride mixture), while ingots of Cr–Mn–N steel are characterized by ferrite–austenite structure, with traces of discontinuous austenite decomposition, accompanied by the precipitation of the nitride Cr2N. Quenching leads to complete austenitization of both types of steel. The agreement of the austenite lattice parameter obtained from the diffraction patterns for quenched Cr–Mn–N steel and the value expected from the concentration dependence for Cr–Mn–N steel indicates that all the alloying elements (including nitrogen) dissolve in austenite as a result of holding at the quenching temperature and are fixed in the solid solution by quenching. Tests of the mechanical properties shows that quenched Cr–Mn–N steel is characterized by both high strength and high plasticity. It may be concluded that reduction of oxides by means of aluminum under nitrogen pressure permits the production of high-nitrogen steel whose mechanical properties match those of corresponding steels produced by electroslag remelting under nitrogen pressure.
102-109
Trends in the Engineering of Blast Furnaces in Modern Fuel and Raw Materials Conditions
Abstract
It is expedient to modify blast furnace profiles so as to better suit new raw materials and fuel additives. Research shows that the shaft height may be increased and the cross section may be enlarged. It is clear from practical experience and the available data regarding the physical and chemical properties of batch components that the inclination of the shaft and the shoulders may be decreased when the batch consists entirely of pellets and pulverized coal injection is employed. With decrease in inclination of the shoulders to 76° at one blast furnace of Yenakiieve Iron and Steel Works, normal thermal conditions may be ensured in the section between the shoulders and the bottom of the shaft over a five-year run after startup.
110-117
Improving Metallurgical Information Systems: Blast-Furnace Applications
Abstract
The creation of smart control systems in the steel industry within the Industry 4.0 framework is considered. Simulation of control systems is a fundamental part of this process. Given existing levels of knowledge, it is not always possible to describe the properties of all the system components and their interactions. Other approaches are required in the simulation of complex energy-intensive processes in pyrometallurgy. As an example, the blast furnace is considered. The main problems in improving information systems in pyrometallurgy are outlined.
118-122
Regulating the Formation of Al2O3–CaO–MgO Inclusions in Pipe-Steel Production
Abstract
Research on Al2O3–CaO–MgO inclusions in steel produced on current systems is reviewed. Analysis of the data shows that magnesium-bearing inclusions of both exogenous and endogenous type are present. Consequently, conglomerates of nonuniform composition are formed. The presence of magnesium in nonmetallic oxide inclusions may largely be attributed to ladle treatment with deep reduction of the metal and slag in chambers with a magnesia lining. Erosion of the refractory lining of steel-smelting and steel-casting equipment must be regarded as a significant factor in the formation of magnesium-bearing inclusions.
123-130
131-133
Neural-Network Analysis of Mandrel Life in a Piercing Mill
Abstract
Statistical analysis is employed to determine the influence of factors such as the distance between rollers in the gorge, the advancement of the mandrel beyond the gorge, the grade of steel in the blank, and the sleeve length on the mandrel life in a piercing mill. The significance of each parameter in the statistical analysis is determined by neural-network modeling.
134-136
Heat Treatment to Slow Strain Aging in Threaded Steel Bolts
Abstract
As a rule, cold-deformed bolts do not contain alloying elements, which slow strain aging. Therefore, natural and artificial strain aging may decrease their resistance to ductile and brittle fracture. The mechanical properties of M12 × 1.75 × 70 mm 1.1152 steel bolts (strength class 5.8) are investigated after strain aging. A method is proposed for slowing the strain aging of cold-deformed steel fasteners: specifically, favorable dislocational structure is produced from the initial structure by heat treatment.
137-140
Precision Alloys and Steels for Medical Use
Abstract
Medical progress calls for improvement in medical steels and alloys. Russian specialists have created medical alloys with no counterparts anywhere in the world. For lack of domestic materials of satisfactory quality, medical enterprises employ imported metals. Closer communication between metallurgists and medical specialists is necessary in terms of the standardization of materials. Medical alloys merit a separate category.
141-146