Том 60, № 3-4 (2016)

Methods of testing bentonite clays as a raw material for the production of pellets are evaluated. A comparison is made between two similar methods – testing based on swellability and testing based on the swell index. It is shown that the quality of clays cannot be properly evaluated based on the obsolete method of swellability and should instead be judged by the swell index on the basis of the amount of time that the clays are in contact with the concentrate. The intrinsic properties of clays are realized to the greatest extent by taking this approach. Arguments are presented in favor of jointly evaluating the properties of bentonite based on the swell index and the Enslin number.

Results are reported from a study of BOF steelmaking at the Cherepovets Metallurgical Combine (CherMK), and the main measures that can make the BOF shop more efficient are described. The measures include improving the logistics of transport operations, the installation of new production equipment, or upgrade of the existing equipment. It is shown that the technical-economic indices of the shop can be improved in a short period of time at minimal cost by adopting a comprehensive approach to modernization of the present facilities.

The temperature fields and stress state of the metal during the rolling of long R65 rails on a modern universal rail-beam mill are modeled in the software suite DEFORM-3D. It is established that the temperature distribution in the finishing passes is quite nonuniform along and across the semifinished product. This nonuniformity creates nonuniform stresses in the elements of the rail profile and is the reason for its bending and twisting (curvature). The nonuniformity of the temperature distribution also causes the mechanical properties of the rail to vary over its length. Technical measures to prevent these problems are discussed.

A model steel microalloyed with vanadium is studied in detail for features of the change in microstructure, mechanical properties, and nanosize carbonitride precipitates in relation to hot rolling parameters. It is established that grain size decreases uniformly and its stretching increases with a reduction in temperature for the end of rolling. The set of steel mechanical properties is decisively affected by the system of nanosize vanadium carbonitride precipitates, including precipitates of three types: interphase, formed during γ→α transformation, and also generated within austenite and formed within ferrite during wound coil cooling.

Features of structure and property formation, processing aspects for preparation of cold-rolled, including hot-dip galvanized, product of two-phase ferritic-martensitic steels with the most typical alloying system (silicon, manganese, and chromium), and also additional alloying with molybdenum, are studied with heat treatment in continuous annealing units (CAU). Cold-rolled product of different thickness is heat treated (HT) in the intercritical temperature range established from results of dilatometric measurements. It is established that there is formation in the test steels of a ferritic-martensitic structure with some proportion of bainite and residual austenite in the form of an MA-component (region with a size of several microns consisting of martensite and residual austenite). With modeling of the HT regime typical for CAU steel alloyed with molybdenum has strength 100–150 MPa higher than steel of the typical alloy system, and this is connected with a higher proportion of strengthening phase within the structure.

The current interest in obtaining metals and alloys with an ultrafine-grained structure is due to the qualitatively new level of their mechanical properties. Since an ultrafine-grained structure is formed as a result of high-rate plastic deformation (HPD), this article presents several alternative definitions of HPD. Continuous HPD methods are the methods that are of practical interest. However, several unresolved scientific-technical, technological, and organizational problems are making it necessary to resort to fundamentally new approaches to developing deformation-based methods of refining microstructural components. This article presents examples of the best-known continuous deformational methods of refining the structural components of metals and alloys. On the other hand, it is also necessary to consider that certain bulk metals and alloys with an ultrafine-grained structure have properties that limit or prevent their practical use. The results obtained from an analysis are used to determine the main avenues being pursued in the development of deformational methods of refining structural components. It is particularly important to consider the use of mini-mills, which can create technological systems based on integrated and consolidated components of modular equipment.

Analytical relations are found for determining the rotation-angle and contact-point-velocity values that the flying plate in explosion welding must have to obtain the limiting uniform strains in the cladding layer. These values determine the parameters of explosion welding and the size of the weld gap. Laminated metallic composites obtained by the explosion-welding regimes proposed in this article have superior wearresistance characteristics during service.

This article examines the problem of the wear of anode pins in a Soderberg electrolysis cell with a top current feed. Wear of the pins reduces the efficiency of the electrolysis operation. Automated monitoring of the geometry of the current-conducting pins is discussed and a method that might be used to monitor their geometric parameters is found. Methods are also found to compensate for the systematic and random errors in the process in order to achieve the required accuracy under the present conditions in an electrolysis shop. A scheme in which elements of the monitoring system are installed on the pin crane is described and a simplified algorithm is developed for the monitoring process.

Results are summarized for a study of technology for preparing finely porous titanium powder no worse in quality than the PTS(A) from screening titanium sponge fraction 0.1 mm produced by AVISMA. It is shown that porous titanium powder physicochemical treatment, including dry magnetic separation and hydrometallurgical leaching, makes it possible to reduce the content of the main impurities to a level answering specifications for titanium powder of fine category A with retention of metal porous structure.

A multi-structural instrument for identifying surface defects on rails has been developed. The instrument operates based on intelligent analysis of video data, and it opens up a wide range of possibilities for using neural-network analysis of images in real time. The instrument can transform a color image into a zero-contrast image, normalize video images, and convert them to binary form. It is distinguished by its real-time noise suppression, evaluation of indicators that provide information on defects, and automatic neural-network classification of defects. The instrument is used together with a dynamic expert system that employs a production model of knowledge representation.

One of the main sources of dust-bearing emissions in the metallurgical industry is the sintering machine. An acoustic field was formed during the initial stage of heat treatment of a sintering-machine charge by using an acoustic radiator in the form of a Hartmann whistle installed in the vacuum chambers of the machine. The acoustic field covers 15–20% of the sintering area and has an acoustic power of 1.0–1.2 kW/m². Use of the field has increased the productivity of the sintering machine 3.2–8.3%, reduced the amount of carbon monoxide formed by 26.7–33.4%, and reduced the entrainment of dust by the gas by 29.2–36.2%. When an acoustic field with a power of 0.3–0.4 W/m³ is created inside the flue-gas collection main, dust emissions can be cut by at least 20–25% of the original value.

This article describes the main principles behind a method developed at the Institute of Ferrous Metallurgy of the Ukrainian Academy of Sciences (IChM NANU) to validate an efficient configuration that was found for the vent system of a 250-ton steel-pouring ladle in the BOF shop at the Dneprovskiy Metallurgical Combine (DMKD). Statistical analysis of production data over a three-year period of use of ladles with such an injection system showed that the campaign of the linings had increased by amounts ranging from 10.7 to 18.8%.

A model steel microalloyed with vanadium is studied in detail for features of the change in microstructure, mechanical properties, and nanosize carbonitride precipitation system in relation to hot rolling, recrystallization annealing, and primarily slow cooling. The possibility is established of the occurrence during rolled product slow cooling of processes similar to recrystallization, leading to a reduction in grain elongation and size, stress relaxation, and formation of a more uniform and equilibrium condition. In addition, due to the formation a considerable amount of vanadium carbonitride precipitates with an average size of 10–15 nm dispersion hardening is realized that provides an increase in strength almost without a reduction in ductility. The intensity of development of the favorable processes described depends to a certain extent on condition of the solid solution formed during steel hot rolling. In addition, an increase in temperature at the end of hot rolling to 830–845°C with a reduction in strip winding temperature in a coil to about 600°C and below leads to improvement of the structural state, and the set of annealed cold-rolled product mechanical properties.

The method of orientation microscopy (EBSD) is used to study the texture of low-carbon, low-alloy pipe steel sheets with a bainitic structure made by controlled thermomechanical processing. The specimens analyzed are inclined or not inclined towards forming separations (secondary cracks) in a fracture during mechanical testing. Formation of separations during failure of steel with a bainitic structure is connected with the presence in the material of regions with uniform orientation (001)<110> extended in the cold rolling direction. Formation of the regions is a consequence of features of γ→α shear transformation that commences at special boundaries between deformed austenite grains.

Optical and transmission electron microscopy (TEM) methods are used for layer by layer comparative analysis of low-temperature reliability rails with increased wear resistance and contact-fatigue strength of the highest quality after bulk quenching and differential hardening by different regimes. Quantitative relationships are established for changes in structural parameters, phase composition, and dislocation substructure over the central axis and fillet at different distances from the running surface. The degree of structure and phase composition inhomogeneity and defective substructure is revealed. It is shown that with respect to structural component content and interlamellar distance the structure after bulk hardening compared with differential hardening is more uniform in a layer 2 mm thick and less uniform at a distance of 10 mm from the running surface. With respect to stress concentration density, the rail structure after bulk hardening (compared with differential hardening) is less uniform in a layer 2 mm thick and more uniform in a layer at a distance of 10 mm from the running surface.

Results are presented from studies of the effect of certain processing factors on the strengthening, reconditioning, and protection of surfaces through the application of coatings by friction cladding. It is established that the use of an electric current speeds up the process, significantly increases the thickness of the coating, and improves its ductility. Combination treatment that entails knurling followed by the application of a functional coating with a flexible tool makes it possible to increase the diameter of a worn part and form an ultrafine-grained structure in its surface layer as a result of intensive plastic deformation.

Powder metallurgy is used to prepare aluminum composites with small additions of Al₂O₃, ZrO₂, MgO, and SiO₂ oxide particles. Sintering is carried out without pressure in a rough vacuum at 640°C. The following material properties are studied: density, porosity, strength in compression, and corrosion resistance in acid solutions. It is shown that with the use of small additions of nanoparticles it is possible to obtain an aluminum composite with relative density up to 98% of theoretical level. It is noted that with compression over the pressing axis a number of aluminum composite specimens containing nanoparticles are unbroken up to the end of testing. Good corrosion properties are demonstrated for aluminum composites with small additions of nanoparticles in 10% nitric and sulfuric acid solutions.

This article discusses research done on modeling, analyzing, and optimizing the technology used to forge the titanium sections of pressure vessels. The finite-element method was used for computer modeling of the deformation of the material during the forging operation. The study examined the forging force, the uniformity of deformation of the vessel’s walls, the filling of the dies, and the probability of crimping. Consideration was given to the possibility of using the phenomenon of superplasticity to forge the given product. The superplastic flow regime is maintained only during the final stage of the forging operation (the last 20% of the stroke of the die) in order to shorten operation as a whole. This is done by setting the die speed at a value which ensures that the material is deformed within a prescribed rate range and that the limits specified for the maximum forces are observed. Several alternatives were examined for making the vessel, these variants differing in the form of the semifinished product and the configuration of the dies. With constraints on the maximum loads and forging time, the technology that was chosen makes it possible to significantly increase the coefficient that characterizes the utilization of titanium in the production process.