Metallurgist (v.61, #11-12)
Prediction of the Fracture of Metal in the Process of Screw Rolling in a Two-Roll Mill by M. M. Skripalenko; B. A. Romantsev; S. P. Galkin; M. N. Skripalenko; L. M. Kaputkina; Tran Ba Huy (925-933).
We study the process of two-roll screw rolling of billets made of stainless steel in order to estimate the influence of the feed angle on the plasticity of the metal of rolling billets. Pilot rollings were simulated by using the DEFORM software. In the computer simulation, the normalized Cockroft–Latham fracture criterion is used to predict the so-called Mannesmann effect (axial fracture of a billet). The comparison of the results of pilot rollings with the data of computer simulations showed that this fracture criterion is an efficient tool for the investigation of screw rolling. A procedure is proposed for the prediction of fracture of the metal subjected to screw rolling.
Keywords: screw rolling; Mannesmann effect; normalized Cockroft–Latham fracture criterion; plasticity; fracture; accumulated strains; stiffness coefficient in the stressed state; computer simulation
Simulation of the Deformation of a Continuously Cast Ingot Depending on the Parameters of Mold Flux by M. P. Gusev; S. V. Zarubin; A. M. Longinov; K. N. Anisimov (934-942).
We propose a mathematical model of the strained state of steel skin, which enables one to evaluate the initiation of transverse cracks in the ingots. The mathematical model is based on the equations of transient heat conduction, relations between the creep strains and stresses in the steel skin, and the integral balance equations. In our calculations, we use industrial data on the thermal work of the mold: the data of thermocouples mounted in the walls of the mold and the integral heat flux computed according to difference between the temperature of water at the inlet and outlet of the mold. The proposed mathematical model takes into account the thermal properties of mold fluxes, their influence on friction between the ingot and the mold, and the creep properties of cast steels as well as establishes the relationship between the parameters of the process of continuous casting and the appearance of transverse cracks in the steel skin. The results of numerical analysis of the limiting state of steel skin are in good agreement with the industrial data on the initiation of transverse cracks in the ingot.
Keywords: continuous casting of steel; limiting state; stress-strain state of the ingot; mold flux; surface defects; transverse cracks; mold
Simulation of the Energy States of Electrolyzers with Roasted Anodes at Elevated Currents by I. A. Sysoev; V. V. Kondrat’ev; T. I. Zimina; A. I. Karlina (943-949).
The technology of electrolysis of aluminum is permanently improved in the direction of increasing the unit power of electrolyzers. The leading aluminum companies over the world try to exploit powerful electrolyzers with roasted anodes operating at current intensities higher than 300 kA because their application improves the ecological and economic efficiency of new plants. The elevation of the current strength aimed at increasing the productivity of an electrolyzers is often restricted by the negative consequences of the influence of thermal loads. To get a stable technology of electrolysis when the power is increased, it is necessary to guarantee the possibility of efficient heat removal from the structural elements. We present the materials on the development and verification of the mathematical model of electrolyzers with a base level of current strength equal to 300 kA. The comparison of the numerical results with the experimental data confirmed the convergence of the values. The power parameters of electrolyzers are obtained for the current strength elevated up to 330 kA. The influence of various engineering decisions aimed at the optimization of the energy state of baths and their influence on the engineering and economic parameters of the process of electrolysis are investigated.
Keywords: aluminum; electrolyzer; simulation; temperature; current strength; voltage; power; interpolar distance; power mode; specific consumption of electric energy
Efficient Management of the Charging of Blast Furnaces and the Application of Contemporary Means of Control Over the Variable Technological Conditions by Yu. S. Semenov; E. I. Shumel’chik; V. V. Gorupakha (950-958).
Under the conditions of unstable qualitative and quantitative compositions of charge materials, we propose an approach to the selection of programs of bell-less top (BLT) charging. It is based on the reduction of the number of working angular positions of the tray and on the shifts (from batch to batch) of the conditional geometric ridges along the radius of the furnace top. A positive experience of realization of this charging program is shown by an example of blast furnace No. 3 at the Enakievo Iron & Steel Works. We discuss the main specific features of mounting of stationary temperature probes with positive temperature coefficient (PTC) on the blast furnaces, as well as the specific features of temperature distributions along the radius of the furnace for various consumptions of the reduced fuel. The relationship between the temperature over the surface of charge bed and the content of pellets in the charge is established.
Keywords: blast furnace; charging program; Bell-less top (BLT) charging; mass flow; ore load; bed height; temperature probe; quality of coke; dusty coal fuel; pellet content of the charge
Selection of the Bell-Less Top Mode of Operation Based on the Data on the Gas Distribution in the Furnace Top and the Shape of the Melting Zone in the Lower Part of the Blast Furnace by A. A. Tretyak; V. M. Parshakov; V. A. Borisenko (959-966).
The collected data on the influence of the parameters of the melting zone on the operation of a blast furnace (BF) give a new look on the formation of guidelines for the choice of the operating mode a bell-less top (BLT) charging system aimed at improving the efficiency of operation of the blast furnace and its lifetime. The management of the “no-feedback” bell-less top operation mode without application of the criteria of BF operation often results in the inefficient usage of its advantages, which sometimes leads to a decrease in the productivity of the BF. The operating control over the BLT charging system aimed at the improvement of the efficiency of BF should be realized with feedback with regard for the changes in the following operating criteria of the BF: optimization of the radial gas distribution in the BF top; minimization of the circumferential gas distribution in the BF top; optimization of the thermal state of the furnace; optimization of the shape and location of the melting zone in the boshes of the BF; monitoring and control of the temperature of materials and smelting products operating in contact with the furnace lining in the boshes, flare, and the bottom part of the furnace shaft. The strategic control over the BLT operation should be performed with realization of the target function, i.e., with an aim to increase the lifetime of the BF by using the following criteria of its operation: the minimization of the FeO content in the primary slag and the optimization of the temperature of materials and smelting products adjacent to the furnace lining in the boshes, in the flare, and in the bottom part of the furnace shaft.
Keywords: blast-furnace smelting; bell-less top charging system; mode of operation; criteria; feedback; radius and circumference of the furnace top; shape of the melting zone
Manufacture of Low-Sulfur Pipe Steel with Ladle Desulfurization of Cast Iron by S. N. Ushakov; V. A. Avramenko; V. A. Bigeev; A. M. Stolyarov; M. V. Potapova (967-970).
A new cast iron desulfurization unit is put into operation in the oxygen converter workshop of Magnitogorsk Metallurgical Combine. Statistically significant linear dependences are established for the degree of cast iron desulfurization on nitrogen injection duration, overall weight of fluidized lime and magnesium, and the weight ratio of fluidized lime and magnesium. An average degree of metal desulfurization of 77.3% is achieved in checking the technology for cast iron ladle desulfurization with injection lasting up to 30 min of fluidized lime and magnesium in a stream of nitrogen with specific consumption of 1.9 and 0.4 kg/ton, respectively.
Keywords: pipe steel; low sulfur content; ladle; cast iron; desulfurization
Using the Properties of One-Sheeted Hyperboloid in Rolls of Sheet Mill Stands by V. N. Khloponin (971-976).
A new technical solution reducing the widthwise thickness variation of a rolled strip is presented. This solution is the use of cylindrical work rolls mounted so that their longitudinal axes cross. The backup rolls have the form of a one-sheeted hyperboloid. Their longitudinal axes are perpendicular to the rolling axis.
Keywords: work rolls; backup rolls; strip; crossing of rolls axes; one-sheeted hyperboloid
Dependence of the Strength of Powder Steel Formed by Electro-Contact Compaction on Iron Powder Preparation Method by T. A. Litvinova; S. N. Egorov (977-981).
Results are presented for the dependence of ultimate strength on electro-contact compaction parameters for an iron-graphite composite based on sprayed and reduced powders. A production regime is determined for electro-contact compaction providing the formation of powder steel with maximum ultimate strength. The dependence of ultimate strength on residual porosity is considered.
Keywords: compactability; interparticle consolidation; iron-graphite composite; ultimate strength; porosity
Features of Material Structure During Manufacture of Billets from Nickel-Base Superalloys Granules by A. M. Volkov; A. A. Buyakina (982-987).
Results are presented for a study of the macro- and microstructure of ingots, granules, and experimental compacted specimens of a new nickel-base superalloy. Features are emphasized most strongly affecting mechanical properties of finished objects prepared from nickel-base superalloy granules, and in fact the size of a dendrite cell, morphology, carbide and γ′-phase size, and solid solution grain size.
Keywords: disk workpiece; GTE; ingot; granule; nickel-base superalloy; structure; grain; γ′-phase; recrystallization; hot isostatic compaction
Study of the Possibility of Preparing Nickel Alloy Polymetallic Material of Different Compositions by Direct Laser Deposition by D. O. Ivanov; A. Ya. Travyanov; P. V. Petrovskii; I. A. Logachev; V. V. Cheverikin; E. V. Alekseeva (988-993).
Currently, direct laser deposition is a key research area since use of this technology is distinguished by cheapness and the possibility of preparing an object of almost any shape. However, numerous aspects of material manufacturing technology and structure formation remain unstudied. The process of preparing polymetallic specimens consisting of layers of alloys Inconel 625 and EP741 is considered. A polymetallic specimen microstructure is extended nickel solid solution crystals. Element distribution in a grain boundary zone shows a smooth change in composition as a result of element diffusion from Inconel 625 alloy into EP741, and conversely. Layer microhardness varies from 300 to 500 HV with transition from Inconel 625 alloy into EP741
Keywords: nickel alloys; additive technology; direct laser deposition; microstructure
Investigation and Computer Design of the Technological Modes of Continuous Rolling of Thin Brass Strips with Specified Accuracy by R. L. Shatalov; A. S. Lukash; A. M. Zaikin; S. P. Zholobov; A. A. Agafonov (994-1000).
We developed a software system for the numerical analysis and design of the technological modes of continuous rolling of copper and brass strips, which enables us to investigate and design the conditions of deformation required to form specified transverse deviations of the thickness of rolled products. We refined the regularities of the influence of various lubricants and the models of distribution of tangential stresses along the contact arc (according to Coulomb and Zibel) on the pressure, rolling forces, and transverse profiles of the strips of L63 brass. We give recommendations concerning the technological mode and contouring of the rolls in a Tandem-1000 continuous three-stand rolling mill-1000 at the Kirov Nonferrous Metals Processing Plant with an aim to reduce transverse deviations of the thickness of thin strips of L63 brass.
Keywords: cold rolling of strips; continuous strip-rolling mill-1000 of the Kirov Non-Ferrous Metals Processing Plant; software system for the design of the parameters of rolling; lubrication of rolls; rolling forces; transverse deviations of the thickness of strips
Melting of Gold-Containing Concentrates with Copper Production Lead Slags by E. A. Mazulevskii; T. V. Kovzalenko; B. Seitkhanov; O. P. Dobryakova (1001-1008).
Results are presented for a study of the pyrometallurgical treatment of gold-arsenic concentrates with lead osmium-rhenium-containing slags. Conditions are found for preparing alloy ingots consisting of lead, or predominantly of lead sulfide, or both phases. It is shown that with gravitation deposition up to 65–68% osmium is concentrated in 17–25% matte. Gold is almost uniformly distributed over the height of ingots. For industrial application of the results obtained, it is recommended that molten products are poured into a mold heated to 500–550°C, and after natural cooling the lower 25% of alloy is separated for osmium extraction, and gold is extracted from the rest of the alloy by well-known technology. Reduction kinetics are studied for gold, osmium, rhenium, and arsenic. According to kinetic curves, recovery of rhenium in slag proceeds rapidly; osmium recovery ceases in 20–25 min; gold is concentrated in the alloy in 10 min. arsenic is transferred into a gas phase in 10 min, and its concentration in alloy comprises 0.2% on average, and in slags 0.27–0.63%.
Keywords: gold-arsenic concentrate; lead osmium; rhenium-containing slag; melting
Development of a New Horizontal Continuous Casting Machine Construction for Nonferrous and Precious Metal Billets by I. Yu. Kryukov; S. M. Gorbatyuk; L. M. Glukhov; A. Yu. Zarapin (1009-1015).
The work is devoted to development of a new design of horizontal continuous billet casting machine (HCBCM) for non-ferrous and precious metals. The possibility of calculation and design of horizontal casting machine elements by means of computer simulation using the software created is demonstrated. Based on the proposed methods of calculation and design as well as analysis of mathematical modeling results, new designs of HCBCM elements are created that enhance the efficiency of the machine. Appraisal trials of HCBCM structural elements created are performed successfully to measure the effectiveness of this work and introduction into production.
Keywords: continuous billet casting machine; crucible; mold; computer simulation of the continuous billet casting; mold cooling device
Evaluation of the Effect of Nepheline Sinter Structure on Hydration Activity During Alumina Production by A. V. Aleksandrov; N. V. Nemchinova; G. G. Mineev; A. A. Yakovleva (1016-1022).
Under conditions for maintaining a stable demand for aluminum in the world, the problem of providing basic high-quality raw material for its preparation, i.e., alumina, remains unresolved. In this connection, work is important aimed at finding ways of improved efficiency for preparing alumina, in particular, by an alkaline sintering method. Experimental data are presented for the defective nature of the structure of different modifications of (α′-, β-) dicalcium silicate 2CaО·SiO2 (С2S), comprising the basis of nepheline sinters. A thermoluminescence method (TSL) is used for C2S specimens prepared with different heat treatment regimes in the range from 1270 to 25°C, and different spectra are established that point to correlation of crystal lattice defect concentration and the degree of test C2S specimen cooling. A correlation is established between the degree of decomposition of different forms of C2S in aluminate-alkaline solution and structural defectiveness evaluated by TSL. It is shown that C2S crystal lattice defectiveness decreases with a reduction in the cooling rate. It is established that β-C2S formed with slow cooling exhibits less defectiveness compared with α′-C2S. Introduction of measures based on results of these studies makes it possible to increase alumina yield and quality used in primary aluminum production.
Keywords: alumina production; sintering; nepheline sinter; dicalcium silicate; thermoluminescence; sinter leaching; aluminate-alkaline solution
Wear and Breakage Resistance of Hard Alloy Coatings Strengthened with Tungsten Carbide by S. A. Sidorov; Ya. P. Lobachevskii; V. K. Khoroshenkov; T. Sh. Akhmedova; D. A. Vorob’ev (1023-1028).
An increase in the wear resistance of soil cultivating equipment components by applying a hard-alloy coating is often used in practice. The good wear resistance of hard alloys is provided, in particular, by the presence of tungsten carbide within them. However, a lack of evaluation of the resistance of these alloys to breakage and life under operating conditions limits their extensive propagation (alongside cost). Results are given in this work for laboratory and operating tests of hard alloys with added tungsten carbide (in combination with hard alloys based on iron and nickel) on wear resistance, and the alloy breakage mechanism with plasma surfacing on soil cultivating machine tool components is evaluated.
Keywords: tungsten carbide; hard-alloy surfacing; wear resistance; breakage resistance; operational tests
Devices for the Formation of Long-Length Products from Powder Materials by L. A. Barkov; M. N. Samodurova; R. A. Zakirov; Yu. S. Latfulina (1029-1032).
The paper is devoted to the design of new devices for the production of long-length bars of consumable electrodes for vacuum-arc melting.
Keywords: device; molding; bar; consumable electrode; refractory metals; powder materials
Correlating Hardness and Welding Dilution with the Abrasion Mass Loss of Hardfacings Welded with Different Currents and Polarities by Hein Zaw Oo; B. Srikarun; P. Muangjunburee (1033-1037).
The correlation of hardness, microstructure, and dilution with the abrasion mass loss of hardfaced samples deposited using different currents (500 and 600 A) and polarities (AC and DC+) was studied. Four different welding conditions were considered for submerged arc welding using a martensitic hardfacing electrode and austenitic buffer electrode. Single-layer hardfacing was applied over the single-layer buffer. The microstructure of hardfacing was observed by an optical microscope. The micro-Vickers hardness across a single-layer hardfacing and dilution percentage were also measured. A dry-sand–rubber wheel abrasion test was conducted according to ASTM G65 procedure A to record the abrasive mass loss of the samples. The use of higher current and DC+ polarity resulted in the highest mass loss because of the deepest dilution and lowest hardness. Dilution affects the hardness and microstructure of hardfacing. The lowest abrasive mass loss, shallowest dilution, and highest hardness were obtained for the sample welded with lower current and AC polarity.
Keywords: hardfacing; martensitic; austenitic buffer; welding dilution; submerged arc welding
Nonmetallic Inclusion Distribution within Ingots for Power Generation Engineering Forgings by N. A. Zyuban; D. V. Rutskii; S. B. Gamanyuk; M. V. Kirilichev (1041-1047).
Results are provided for a study of the distribution and location of nonmetallic inclusions in large forgings of steel 38KhN3MFA weighing 24.2 and 23.52 tons with a normal configuration and with a changed shape of the bottom part (“convex” bottom) cast in a vacuum. It is shown that the change in ingot bottom section geometry leads to an increase in temperature gradient and as a consequence to an increase solid phase advance intensity. In turn, this leads to more uniform distribution of oxysulfide inclusions. The sulfide inclusion content in the ingots compared increases from the periphery to the ingot axis. Dependences are obtained for metal ductility properties, i.e., relative elongation, relative reduction of area, and impact strength on sulfide inclusions distribution over ingot levels, and their unfavorable effect on these properties is established. It is shown that a reason for the reduction in ductility properties is sulfide phase location in the form of films of dendrite boundaries that occurs under conditions of a shortage of oxygen in the melt. This leads to a reduction in oxysulfide content and formation of a sulfide component in an unfavorable form distributed over cast grain boundaries. The ingots are destined for domestic power generation engineering forgings.
Keywords: large ingot; solidification; nonmetallic inclusions; ductility properties; oxides; sulfides; oxysulfides
Effect of Continuous Casting Technology on Low-Alloy Steel Structure in Different Production Stages by A. N. Zavalishchin; E. V. Kozhevnikova (1048-1054).
The effect of “soft reduction” technology on chemical inhomogeneity of a continuously-cast slab, and also on the structure and properties of finished rolled product made of low-carbon microalloyed steel is studied. In slabs prepared without soft reduction, a defect is often observed in the form of white bands leading to a reduction in the proportion of ductile component in low-standard rolled product. In a slab transverse section, from the surface into the depth there are coarse grains with ferrite over boundaries and bainite within grains. A white band is formed by fine polyhedral ferrite grains with a small amount of finely acicular bainite. In this case, the microhardness of ferrite and bainite in the axial zone, and in a white band is considerably higher than in other slab zones. Also within the limits of a white band there is formation of an increased amount of sulfides and carbonitrides. It is demonstrated that as a result of liquation processes there is an increase in carbon, manganese, sulfur, and phosphorus, and also microalloying element content within a white band.
Keywords: low-alloy steel; continuously-cast billet; soft reduction; liquation; microstructure; hot-rolled product
Flow Characterization and Inclusions Removal in a Slab Tundish Equipped with Bottom Argon Gas Feeding by C. E. Aguilar-Rodriguez; J. A. Ramos-Banderas; E. Torres-Alonso; G. Solorio-Diaz; C. A. Hernández-Bocanegra (1055-1066).
The fluid dynamics of a straight tundish was studied when Ar-gas was fed through the bottom, using mathematical simulation. Flow rates of 15 and 40 liters/min of argon in three locations into the tundish – near input steel, center, and near output steel – were analyzed. A stochastic model was employed for determining statistically the particle amount (emulating alumina particles) in the inclusions removal. From these calculations and those of the Residence Time Distribution (RTD) curves, we found a direct relationship to improve steel quality. Specifically, removal of the smaller nonmetallic inclusions was significantly enhanced for cases with the lowest dead volume fraction; they correspond to those of the highest averaged residence time. Therefore, it was found that it is even possible to reduce argon consumption and still obtain good results of steel cleanness.
Keywords: tundish; inclusions removal; gas injection
Control over the Formation of Continuously Cast Billets with the Use of Vibrating Molds in Machines for Continuous Casting by A. S. El’darkhanov; A. S. Nuradinov; S. S.-S. Akhtaev (1067-1074).
For AD31 aluminum alloy, we study the influences of the shape of the heat-removing surface of the mold and its vibration on the formation of cast billets. It is shown that both factors significantly decrease the area of columnar crystals, lead to grinding of the macro- and microstructures of billets, and improve the properties of the metal. It is shown that the vibration treatment of a billet almost removes the anisotropy of properties over its zones.
Keywords: billet; mold; vibration; artificial roughness; structure; properties
Theoretical Foundations of the Design of a Lever Mechanism of Oscillations of the Mold of a Sorting Machine for the Continuous Casting of Billets by A. L. Sotnikov; A. B. Kikin (1075-1083).
We consider specific features of the design of the lever mechanism of oscillation for the mold of a radial sorting machine with continuous casting of billets under the conditions of the maximum correspondence of the vibration motion of the mold with the axis of extrusion of ingots from this mold. It is shown that the traditional kinematic scheme of the oscillation mechanism does not guarantee high accuracy of the codirectional motion of the mold relative to the technological axis of the channel of this machine.
Keywords: mold; oscillation mechanism; design; kinematic synthesis; technological axis; trajectory; length of the links; location of the mold; base radius
Effect of Structural State and Temperature on Crack Generation and Propagation Resistance in Pipe Steels by A. R. Mishet’yan; I. P. Shabalov; O. N. Chevskaya; G. A. Filippov (1084-1092).
Comparative research of microstructure and properties of different strength classes of plate steels produced by controlled rolling with accelerated cooling is performed. Standard mechanical properties, ductility parameters, and cold resistance are determined. The relaxation effect for pipe steels is evaluated. It is shown that structural heterogeneity has an unfavorable effect on brittle failure resistance due to the formation of local stresses of higher level that arise under the action of loading in the elastic region.
Keywords: low-carbon low-alloy pipe steels; microstructure; banding; stress relaxation; cold resistance
Study of Low-Carbon Pipe Steel Strain Ageing by I. Yu. Pyshmintsev; M. A. Smirnov; O. V. Varnak; A. N. Mal’tseva; Yu. N. Goikhenberg (1093-1101).
Strain aging of pipe steels 06G2FB and 07G2MFB with ferrite-pearlite and ferrite-bainite structures is investigated. It is established that a ferrite-bainite structure is more inclined towards strain aging than a ferrite-pearlite structure. The tendency towards strain aging of steel with a ferrite-bainite structure increases with increasing austenitizing temperature. During hot plastic deformation there is development of recrystallization and the tendency towards strain aging decreases.
Keywords: low-carbon pipe steel; strain aging; ferrite; bainite; mechanical properties; austenitizing temperature; hot plastic deformation
Analysis of Drive Mechanisms for the Working Stand in Periodic Cold-Rolled Pipe Mills by A. G. Kolesnikov; D. S. Cherepanov; A. V. Chekulaev; M. O. Mironova (1102-1107).
We discuss several drive mechanisms for the working stand in periodic cold-rolled pipe mills. This paper focuses on identifying opportunities to increase mill capacity and modernize existing periodic cold-rolled pipe mills. We provide a comparative analysis of a variety of systems for equilibration of the dynamic forces in the working-stand drive mechanism.
Keywords: cold rolling; CPT mill; crankshaft/rod drive mechanism; dynamic load; increasing the productivity
Elevation of the Wear Resistance of Threads of Tubing Strings Under the Action of Ultrasound by V. A. Morgunov; S. M. Nebogov; I. L. Fedotov (1108-1114).
We developed a technology, produced, and tested an ultrasonic installation aimed at treatment of the pipe threads with the help of radial ultrasonic vibrations and studied the microhardness of the outer surface of the thread profile. We also performed metallographic investigations. The pilot field tests of the branch pipes of tubing strings with strengthened threads were carried out and positive results were obtained.
Keywords: ultrasonic hardening of the pipe thread; surface plastic deformation of the profile of the thread; microhardness; nanocrystalline layer; strength of threaded connections; tubing strings
Preparation of Aluminum-Scandium Master Alloys by Aluminothermal Reduction of Scandium Fluoride Extracted from Sc2O3 by B. P. Kulikov; V. N. Baranov; A. I. Bezrukikh; V. B. Deev; M. M. Motkov (1115-1121).
Aluminium alloys containing small additions of scandium exhibit unique operating properties. Alloying material with scandium significantly improves product weldability, reduces the tendency towards hot cracks and improves welded joint mechanical properties. The aim of this work is to increase the scandium extraction into a master alloy by preliminary transformation of scandium oxide into fluoride and introduction into the composition of an aluminium powder alloying additive. Results are provided of laboratory experiments for preparation of aluminium-scandium master alloy by aluminothermic reduction of scandium fluoride using sodium fluoride and aluminium powder within the alloy composition. Scandium fluoride is prepared by treating scandium oxide with 40% hydrofluoric acid. The overall extraction of scandium from oxide into fluoride and from fluoride to the aluminium-scandium master alloy is 88.5% with an average scandium concentration in the master alloy of 1.90 wt.%. The microstructure of the master alloy obtained is represented by scandium aluminide Al3Sc crystals with a size from 10 to 25 μm uniformly distributed within the master alloy. An additional reserve for increasing the extraction of scandium into the master alloy and reducing its cost is processing of slags formed in the preparation of the ligature. The use of an aluminium powder with high specific surface area in the composition of the alloying additive increases scandium extraction into the master alloy due to better contact of the reacting phases. The resultant Al–Sc master alloy has uniform distribution of Al3Sc particles within the volume of the metal.
Keywords: aluminium-scandium master alloy; scandium oxide; scandium fluoride; aluminothermic reduction; sodium fluoride; scandium aluminide; standard electrode potential
Prospects of Production of Granular Composite Materials by Method of the Plasma-Centrifugal Atomization by S. V. Bogdanov (1122-1129).
We discuss the prospects of development of the complex approach to the design of high-density, structurally homogeneous hard materials produced from granules obtained on plasma-centrifugal atomization installations with formation of molten baths from the melts in rotating crucibles with skull. The analyzed technology and equipment prove to be promising and commercially attractive for the production of granules intended for manufacturing monolithic composite materials. Granular compositions obtained from spherical particles by using known methods of compaction or layer-by-layer synthesis can be in demand in the domestic industry.
Keywords: granules; spheroids; plasma-centrifugal atomization; crucible; skull; composite materials; closest packing; compaction
Predicting the Risk of Destruction of Hard-Facing Alloys Based on the Morphology of Their Structure by A. S. Mel’nichenko; A. V. Kudrya; T. Sh. Akhmedova; E. A. Sokolovskaya (1130-1134).
Wear resistance and fracture resistance are the main indicators of the quality of hard alloys. The risk of fracture of such materials is usually difficult to assess due to high hardness. However, this can be done by measuring the morphology of microstructure. The structure of hard alloys is diverse. Hardening particles (carbides, borides, particle clusters, dendrites, etc.) are located in the matrix. They have different geometries, the thickness of matrix interlayers varying. This assumes using a statistical approach to the analysis of structures. The statistical nature of structural elements is established with digital optical microscopy. Objective methods for the binarization and filtration of structure images are proposed. It is shown that the average thickness of the interlayers and the asymmetry of the thickness distribution can be used as an effective assessment of the risk of fracture of hard alloys. The prediction of the risk of fracture is validated by comparing the morphology of structures and fractures of hard alloys.
Keywords: hard alloys; hard-facing; risk of fracture; heterogeneity of microstructures; statistics; critical strain; fracture