Том 61, № 11-12 (2018)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.