The article provides a brief overview of the properties and production technology of high-nitrogen steels (HNS), which have several advantages over traditional ones. The main advantages are: up to four times higher yield strength with unique preservation of the remaining characteristics; reduction in consumption or a 100  % elimination of the use of some expensive alloying elements, such as Ni, Mo, Co, W, and others; effective alloying with unconventional elements (Ca, Zn, Pb, etc.). The basics of HNS technology, dependence of the properties on nitrogen content in steels, producing technologies for ferritic-pearlitic, martensitic and austenitic steel, their properties and applicability are discussed. Alloying with nitrogen for ferritic-pearlitic steel requires more precise adherence to the chemical composition in order to prevent the formation of insoluble nitrides during heat treatment (due to its greater solubility compared to carbon). Features of martensitic steels are associated with the possibility of formation of nitrides and carbonitrides during tempering. The possible effect of nitrogen in these steels may be as a decrease in the size of nitride particles as compared with carbide ones. Increased stability temperature of nitrides and carbonitrides provides increased mechanical and physical properties. In austenitic steels, nitrogen, due to the strong γ-forming equivalence to nickel, replaces it in a ratio of 1  kg of nitrogen  ≈  6  –  39  kg  Ni. In austenitic-martensitic steels, the main role is played by thermal martensite. Stable austenite is obtained in the process of its aging at operating temperatures. Examples of effective use of HNS in important details are described.

A method for calculating the modes of strips cold rolling on multiple-stand (reversing) rolling mill is considered providing minimum power consumption with maximum process stabilization at high speeds and obtaining the given quality of cold-rolled strips (minimum probability of surface defects, compliance with thickness tolerances and flatness requirements of the used standards). The problem is solved using the conditional optimization method. As an optimization criterion, it is proposed to use the total energy expenditure spent on the rolling process, as conditions – technological and structural limitations on the rolling parameters and conditions of strips stability to breaks and surface defects formation. The decision to develop this innovative method is due to the fact that a large number of existing approaches to calculation and design of rolling modes have visible advantages and disadvantages. In many cases, the researchers are trying to take into account several requirements that ensure stability of rolling process, its quality, the equipment operating conditions, reduction of energy consumption, metal, auxiliary materials and the specified (maximum) mill productivity. However, some of these requirements can be contradictory and the best one will be the mode that with a high degree of probability guarantees the fulfillment, in a certain proportion, of the entire set of requirements. Therefore, such calculation method is the presented in this article. Calculation of the cold rolling regimes was limited to selection and distribution of the crimping along the cages (passages in the reversing mill). Also, the strip strains are selected in the intercellular spaces, on the decoiler and coiler, and in setting the speed wedge in a particular system of constraints imposed on the input and output process variables as a function of the adopted optimality criterion. As it was noted earlier, the problem was solved with the help of the conditional optimization method with specification of the optimization criterion.

For straightening of low-rigid cylindrical details like shaft and axes different types of loadings are considered which form tension different in size and in distribution. As the perspective direction, it is possible to consider correction by a bend at the influence of the distributed loading with the subsequent hardening of a billet by superficial plastic deformation based on a cross cheesing of it by flat plates. Purpose of the work was to define tension of the billet at cross correction for the choice of more effective type of loading and processing rational modes. The mathematical apparatus was used based on laws of the theory of an elastoplastic solid and Ansys Workbench software package. Novelty is the research of effective methods of loading at cross correction of cylindrical details. As a result of analytical calculations, value of the residual tension providing correction of cylindrical details was determined. Residual tension necessary for correction of cylindrical details depends on an initial deflection, material and preparation rate. Tension of cylindrical details was defined depending on a type of the application of cross loadings. Bend tension for correction of a shaft at distributed loading is less, than tension from action of cross force. For correction of a shaft with a diameter of 10 mm, 200  mm long and an initial deflection of 0.5  mm it is necessary to create bend tension equal to about 370  MPa. An effective method of loading at cross correction of cylindrical details is the bend at influence of the distributed loading. The received extreme values of bend coefficients are from 5.3 to 5.5 for all cases of shaft rigidity at correction by cross bend at distributed loading with l/L relation equal to 0.8. The developed mathematical model gives quite reliable values of the residual tension providing correction of cylindrical details. The analytical dependence for determination of the size of general deflections and definition of an effective loading type can be recommended for practical use in production for achievement of precision accuracy of low-rigid details like shaft.

The second part of the article considers influence of the scrap amount on structure and mechanical properties of ZhS6U-VI nickelbased superalloy. As the use of scrap is associated with the possibility of alloy contamination by nonmetallic inclusions and loss of alloying elements, the influence of scrap on alloy structure and mechanical properties is in great importance. The samples with diameter of 12  mm were melted in a vacuum arc furnace and were casted into a copper mold from the virgin ZhS6U-VI alloy without scrap and from alloys with 50  % and 100  % of scrap. The alloys structures were investigated using optical microscopy on etched metallographic sections that were cut from the samples’ cross-sections. The studies were carried out on the as-cast samples and the samples after solution heat treatment for 4  hours at 1210  °C. The slightly higher nonmetallic inclusions content were observed in the structure of the alloy melted with scrap in comparison with virgin alloy melted without scrap. For the sample that was melted from 100  % of scrap the inclusions secure level is 3 (ASTM E 45-97) with an average size of inclusions of 28.4  ±  0.2  μm. Herewith the presence of single large inclusions with a size of not more than 70  microns was noted. However, it has no effect on the alloy mechanical properties. Mechanical properties after heat treatment (ultimate strength (UTS)  =  1090  –  1100  МPа and elongation (El)  =  9  –  11  %) were obtained on the samples melted using 50 and 100  % of scrap and fully correspond to the TU1-92-177-91 standard for ZhS6U-VI nickel-base superalloy. During solidification most of the large nonmetallic inclusions are concentrated under casting surface, which makes their machining difficult. Because of that the use of 100  % scrap without its preliminary processing is not recommended. Acceptable results were achieved when the 50  % of scrap was used.

 

The results of theoretical and physical modeling of pipes forming process are described. Experiments on strip billets forming were carried out on 10-50 pipe-welding mill for a pipe 50 mm in diameter with 1mm wall. Forming of pipe billets was carried out at unit of forming horizontal and vertical stands with estimation of geometrical parameters. Roll drafting is one-radial. Energy-power parameters of the process that affect quality of billet geometry were determined and measured. Analysis of geometric parameters of resulting billet has revealed defects of buckling type on the billet’s right edge between the second edger and the third molding stand. Similar defect was detected at the left edge of the billet at a distance of the third molding and edger stands. To eliminate defects in forming section, shaping stands were rebuilt so that forces on drive cells were identical. Energy-force parameters of the process were sequentially determined: pulling forces of drive stands, resistance to strip movement and vertical molding forces. Calculations for determining energy-force parameters were performed taking into account the main technical parameters using two methods. The first technique takes into account geometric parameters of molded billet and parameters of working zone with the zone of non-contact deformation. The second method is based on consideration of contact interaction between the billet and shaped instrument along the deformation section. Discrepancy between calculated and experimental data was 8  –  12  %. After adjusting technical parameters of the molding process and the passes re-adjusting, a defect-free pipe billet was formed. Comparative analysis of calculated and experimental edge trajectories along the height and width of the cages showed discrepancy in results in range of 6  –  9  %. While studying geometric parameters of the focus of deformation, contact and non-contact zones of working zone and area of sprinkling were taken into account. Parameters of the pipe billet shaping in monotonous and roll forming centers have been calculated. Analysis of the results has shown that change in billet’s geometry in shaping stand corresponds to the accepted statements of billet’s geometry changes in rolling pass.

The authors have made an analysis of problems arising in the rolling of continuous-cast billets in the modern mini-metallurgical and rerolling plants. It is shown that the use of trio stands in rolling mills of these plants makes it necessary to obtain billets of multiple lengths from bars (most often of 12-meter length) produced in the rolling shop. The subsequent rolling of such multiple billets has revealed increased cracking of the front edge and, as a result, increased metal consumption. Analysis of the causes of these cracks has been made. It was indicated that this defect can appear as a result of a certain stress-strain state formed at the end of hot-rolled breakdown. It is caused by the presence of an uneven temperature field due to more intensive end cooling, to reduction mode in the trio stand and to the presence of axial defects in the continuous-cast billet. The study was conducted on the industrial medium-grade mill 500/370, as well as using mathematical modeling by finite element method. The influence of a set of technological factors, such as temperature of the billets heating before rolling, the time interval of their transportation on the site “heating furnace – first stand of the rolling mill” and parameters of the macrostructure of axial area of the metal were investigated. Calculations by the developed mathematical model have indicated the need to take into account the presence of a scale layer on the heated continuous-cast billet. It is shown that depending on the heating temperature and transport time, the temperature difference at the billet’s end compared to the heating temperature can be from 45 to 100  °C. It will lead to an uneven distribution of deformation resistance and unfavorable stress-strain state at the billet’s end. In addition, the presence of an axial defect can affect the cracking because of its shape and its transformation during reduction. Obtained experimental data allowed hypothesizing the mechanism of transformation of discontinuity defects into cracks at the billet’s end due to the conditions of continuous casting and cutting of billets during rolling in the reduction stand.

The article describes the magnesian fluxes properties of the Khalilovo deposit with different proportions of magnesite and serpentine. The results of laboratory experiments on the effect of these fluxes with various magnesite contents on the parameters of sintering process of the Kursk magnetic anomaly ores at JSC “Ural Steel” are presented. The use of experimental magnesian fluxes of the Khalilovo deposit increases the sinter strength, yield and sinter productivity. With the use of experimental fluxes instead of Bakal siderite, an increase in the sinter yield of 3  –  5  %  (rel.) can be reached. In addition, the sinter productivity increases from 1.04 to 1.08  –  1.15  t/(m2·h), that is, by 4  –  10  %  (rel.). The use of experimental magnesian fluxes increases the sinter strength: the tumbler index (+5  mm) increases by an average of 4  –  6  %  (abs.), and the abrasion index (–0.5  mm) decreases by 0.6  –  0.8  %  (abs.). Improving the strength characteristics of the sinter using magnesian fluxes of the Khalilovo deposit is due to the formation of “reinforcing” ferritic binder, as well as due to homogenization of the solidifying melt and its crystallization in the form of glass phase of the rankinite composition, which together limit the formation of β-Ca2SiO4 . The results of experimental sintering have confirmed the possibility of using experimental fluxes in the sintering production at sinter plant of JSC “Ural Steel” without changing the production technology. The rational variant for JSC “Ural Steel” is 50  % of magnesite of Khalilovo deposit in sinter rawmix. Replacement of the Bakal siderite in the production of sinter with 2  % of MgO on the magnesian flux of the Khalilovo deposit with 50  % of magnesite provides an increase in yield by 4  –  5  %, an increase in sinter strength by 5  –  6  % and an increase in sinter productivity by 8  –  10  % while keeping the iron content at the level of the “base” period.

The article describes the magnesian fluxes properties of the Khalilovo deposit with different proportions of magnesite and serpentine. The results of laboratory experiments on the effect of magnesian fluxes of the Khalilovo deposit with various magnesite contents on the parameters of the sintering process of the Kursk magnetic anomaly ores at JSC "Ural Steel" are presented. The use of experimental magnesian fluxes of the Khalilovo deposit increases the sinter strength, increases the yield and sinter productivity. With the use of experimental fluxes instead of Bakal siderite is provided increase in the sinter yield of 3-5% (rel.). In addition, the sinter productivity increases from 1.04 to 1.08-1.15 t / (m²·h), that is, by 4-10% (rel.). The use of experimental magnesian fluxes increases the sinter strength: the tumbler index (+5mm) increases by an average of 4-6% abs., and the abrasion index (-0,5mm) decreases by 0.6-0.8% abs. Improving the strength characteristics of the sinter using magnesian fluxes of the Khalilovo deposit is due to the formation of a "reinforcing" ferritic binder, as well as the homogenization of the solidifying melt and its crystallization in the form of a glass phase of the Rankinite composition, which together limit the formation of β-Ca₂SiO₄.

The results of experimental sintering are confirmed the possibility of using experimental fluxes in the sintering production at sinter plant of JSC "Ural Steel" without changing the production technology. The rational variant of magnesian component of the sinter raw-mix is magnesite of Khalilovo deposit with 50% magnesite content for JSC "Ural Steel". The replacement of the Bakalsk siderite in the production of sinter with 2% MgO on the magnesian flux of the Khalilovo deposit with 50% magnesite is provides an increase in yield of 4-5%, an increase in sinter strength by 5-6% and an increase in sinter productivity by 8-10% while keeping the iron content at the level of the "base" period.

A method of calculating the cold rolling schedules of strips on a multiple-stand rolling (reversible) mill is provided which can provide a minimum power consumption with maximum process stabilization at high speeds and obtaining a given quality of cold-rolled strips (minimum probability of surface defects, compliance with thickness tolerances and flatness requirements of the standards used). The problem is solved using the conditional optimization method. As an optimization criterion, it is proposed to use the total energy expenditure spent on the rolling process, as conditions, technological and structural limitations on the rolling parameters and the conditions for the stability of the strips with respect to breaks and the formation of surface defects. The decision to develop this innovative method is due to the fact that a large number of existing approaches to the calculation and design of rolling regimes have visible advantages and disadvantages. In many cases, the developers are trying to take into account several requirements that ensure the stability of the rolling process, the quality of the rolling, the operating conditions of the equipment, the reduction of energy consumption, the metal, the auxiliary materials and the specified (maximum) mill productivity. However, some of these requirements can be contradictory and the best one will be the regime that with a high degree of probability guarantees the fulfillment, in a certain proportion, of the entire set of requirements. This is the method of calculation presented. The calculation of the cold rolling regimes was limited to the selection and distribution of the crimping along the cages (the passages were in the reverse mill). Also, the strip strains are selected in the intercellular spaces, on the decoiler and coiler, and in setting the speed wedge in a particular system of constraints imposed on the input and output process variables as a function of the adopted optimality criterion. As it was noted earlier, the problem was solved with the help of the conditional optimization method, that is, with the specification of the optimization criterion. As an optimization criterion, it is proposed to use the total energy expenditure spent on the rolling process, as conditions, technological and structural limitations on the rolling parameters and the conditions for the stability of the strips with respect to breaks and the formation of surface defects.

The use of galvanized scrap as a charge material for electric steel-smelting production leads to the formation of metallurgical dust suitable for the extraction of non-ferrous metals. The issues related to the behavior of chlorine and its compounds in zinc and lead containing EAF-dust is not sufficiently studied. Current research exhibits the danger of chlorine and its compounds in charge and, consequently, in emissions of EAF. Chlorine and its compounds are considered to be the main components associated with the formation of highly toxic organic substances – dioxins and furans (D&F). D&F enter the environment not only in gaseous form, but also in the form of compounds adsorbed on the surface of dust particles. According to various data, D&F concentration is 5-500 ng / kg of dust and depends on the technological parameters of melting. Analysis of the formation processes of D&F in EAF and their behavior in the captured dust is given. It was found that at the studied chlorine content of 1.3% in EAF-dust from the charge materials, 99.9% of chlorine form relatively safe compounds, mainly chlorides, and a small amount goes to the formation of D&F. The amount of D&F adsorbed on the surface of captured dust particles was 474 ng / kg of dust. As strong toxicants, D&F increase the hazard category of dust from the 4th to the 3rd and above that must be considered at dust usage. In addition, the transport of D&F in the environment is due to solid particles that absorb poisons on their surface. Therefore, EAF dust, with D&F adsorbed on its surface, can provoke their entry into organisms. The ways of reducing D&F emission in the production of EAF-steel and the resource-saving and environmentally safe technologies of dust processing are considered. In particular, the possibility of using lime milk for the off-gases irrigation in the EAF gas flue was analyzed and it was shown that it allows to reduce the D&F content to acceptable limits. The efficiency of the proposed activities was evaluated.

During the implementation of strategic research program of the Technology Platform “Closed Nuclear Fuel Cycle with Fast Reactors”, hot cells are fitted with original non-standard equipment for primary post-reactor non-destructive studies of critical fast reactor materials. These materials include chrome-iron alloys, considered as promising for fuel rod cladding of fast neutron reactors. During the investigation via the ultrasonic spectroscopic method of internal friction of cylindrical samples from chrome-iron alloys in a narrow temperature range near 550 K at their cooling with rate of about 0.2 K/s, we have revealed an anomalous effect from the point of view of oscillations classical theory. Its peculiarity consists in the occurrence of coupled oscillations in samples with a nonuniform temperature distribution along the radius, in case the interval of temperature variation contains the point of the magnetic phase transition of the material. Such a sample can be considered as a complex oscillatory system consisting of peripheral (cooler) and central areas in different magnetic states, with a pulsating interface, on which mechanical stresses act. It was estimated that this anomalous mode of oscillations is associated with the influence of dynamic vibrational stresses on formation and magnetic phase transformations in carbonitride inclusions occurring during heat treatment of alloys. A theoretical description of this effect is proposed. It is shown that by registering the parameters of coupled oscillations, it is possible to estimate the sizes of the resulting phase inclusions. The discovered features and established regularities of resonance oscillations in combination with the traditional method of internal friction can be used to detect metastable phase inclusions occurring at intermediate stages of the material structure, and to estimate their sizes. It will undoubtedly be useful in the case of primary non-destructive tests in hot cells of heavily irradiated samples of these alloys when optimizing their composition for fuel rod claddings of fast neutron reactors.

The article presents one of the possible options of mathematical model formation of an electric arc steel-making furnace (EAF). A lot of reports on this subject were studied in order to make a model that most accurately reflects the control object behavior (for EAF). The basic building principles demonstrate the fact that the primary element is substitution pattern of electric circuit of the installation. Cassie nonlinear differential equation was used to get a mathematical model of an electric arc. This nonlinear differential equation is very popular among the researchers. Model update is provided by calculating the electrical circuit parameters on the secondary side of transformer low voltage and by studying statistics from home and foreign scientists’ contributions. Different values of the “time-constant” of arc conductivity were used to analyze the control object behavior at different instants of time. It made it possible to take into account the nonstationarity of the state of electrode sheaths that were influenced by external disturbances, temperature variations, pressure and gas composition in the course of production processes. Such an approach made possible to form an aggregate picture of the control object behavior under the conditions of a nonstationary state of the arc combustion area at different stages of melting; to evaluate possible regulation characteristics and to determine control system requirements. The structural scheme of the model of a three-phase AC–EAF was formed. All necessary calculations of circuit elements and modeling were performed using the MATLAB Simulink package. The block diagram includes AC voltage source, direct-current resistance, and inductance of the transformer on secondary side and a low-voltage circuit, a model of an AC electric arc. The model was used to analyze the dynamic characteristics of electric arc as being an electrical object to show the voltage–dependence of current – current-voltage characteristics. The configuration of current-voltage characteristics determines burning behavior of the arc, existence domain, stability and control quality. Current-voltage characteristics were studied under the conditions of different values of the voltage on the secondary side of transformer and arc length and for different values of the “time-constant arc conductivity”. The model was also used to analyze the static characteristics. The dependence of the arc length on the current for different voltage of the transformer steps is nonlinear. Recommendations on the choice of control actions and the construction of control systems for different stages of melting are given. For example at the initial stage of melting, the control system should perform minimization problems of number of breaks under the condition of an insignificant domain of the arc existence and limit the value of lead-in power. The simulation results show that the nonstationarity of the process leads to the need to use self-organizing control systems capable of adjusting to the continually varying state of the object.

Metallurgical conversion methods are still missing iron ore with heterogeneous structure magnetite of the Kovdor deposit. Sintering mechanism of Kovdor concentrate was investigated in the wide CaO/SiO2 basicity range of 1.2  –  3.0 for sintering process conditions. Main influence of magnetite crystal structure on the way of charge phase changing in sintering process is shown for the first time. As a result of sintering with the low basicity of 1.2  –  2.0 two phases sinter system was formed, containing magnetite and silicate bond of melilitic composition. The analysis has shown that melilitic bond is the straight analog of the basic and acid blast furnace slag. The difficult mineral composition, containing four phases, is formed with the high basicity of 2.0  –  3.0. Magnetite and bond of crystals of calciumalumosilicoferrite are the main minerals, which occupy almost the whole volume of the sinter. By composition and number of phases, magnetite-ferritic composition is two-phase sinter system. Development of appropriate sintering process regimes is required for each of the determined sinter systems.