A promising direction for production of simple profiles by rolling includes grooveless rolling. Due to the use of forming in smooth rolls, this direction significantly reduces the production cost of finished products and simplifies the rolling process. However, despite all the obvious advantages of deformation in smooth rolls, there are disadvantages that complicate industrial implementation including the need for edging after each pass and a small coefficient of extraction in smooth rolls. It causes an increase in the number of passes. For the solution of problems encountered in current industrial implementation of grooveless rolling, it is proposed to use deprived-wide vertical stands in continuous groups. Deformation in non-water vertical stands is provided by more complete use of the reserve of contact friction forces of the drive stands installed in front of them. The conditions under which the use of non-water vertical stands is possible are determined. After solving the equation of forces equilibrium on the contact surface in the deformation center of the drive stand, dependence is obtained by which it is possible to find the value of longitudinal force provided by reserve of friction forces. By solving the equation of power balance in form of non-drive rolls, the dependence is obtained determining the longitudinal force required for deformation. The authors offer the dependence by which it is possible to determine the maximum allowed distance between the drive and non-drive stands, providing longitudinal stability of the strip. Using dependencies to determine conditions of deformation in horizontal drive and non-driven vertical mills with smooth rolls, reduction modes during rolling of rebar No. 12 in conditions of JSC “EVRAZ ZSMK” 250 continuous light section mill using roughing stands for grooveless rolling were calculated. As a result it was found that the use of non-water vertical stands allows rolling of larger cast billet of 125x125 mm square on the mill. Economic component of transition to the larger cast billet with development of grooveless rolling was estimated. Advantages of the proposed solutions are shown in comparison with classical method of rebar No. 12 rolling on 250 continuous small-grade mill of JSC “EVRAZ ZSMK”.

The article presents the reasons of strength reduction of welded joints of reinforcing bars of A500C strength class. The joints were made of reinforcing steel with a diameter of 12 mm, with one of the joints made of thermomechanical hardened steel (sample 1), and the other – of hot-rolled steel without further processing (sample 2). It was established that the structure of welded joint 1 is characterized by the presence of products of tempering of martensite – martensite-bainite structure with hardness of 327 – 339 HV. Characteristic needle and packet formations are observed. The weld metal (core) has a structure identical to the structure of heat-affected zone on the overheating area. The structure of welded joint 2 is represented by more expressed zoning. The boundary is traced between the weld metal (core) and the heat-affected zone. In plane of the section, the cast core is observed as a thin light layer of 30 – 40 microns thickness and with hardness of 180 – 190 HV; it consists of ferrite, not fully subjected to post-welding heat treatment. Also slag inclusions present in all volume of the welded joint metal. In the heat affected zone, in the area of overheating the widmanstatten bainitic structure is also observed. Metal hardness of the heat-affected zone is at the level of 250 – 265 HV. The most likely reasons for the reduced strength of welded joints are increased fragility of the weld metal and the zone of thermal influence, due to the high hardness, more than 300 HV, as well as the presence of slag inclusions in the weld metal of the joint (core), which act as stress concentrators and under external loads are a source of destruction.

Effect of carbon and oxygen impurity atoms on diffusion along the tilt grain boundaries with <100> and <111> misorientation axis in metals with FCC lattice was studied by mean of molecular dynamics method. Ni, Ag, and Al were considered as metals. Interactions of metal atoms with each other were described by many-particle Clery-Rosato potentials constructed within the framework of tight binding model. To describe interactions of atoms of light elements impurities with metal atoms and atoms of impurities with each other, Morse pair potentials were used. According to obtained results, impurities in most cases lead to an increase in self-diffusion coefficient along the grain boundaries, which is caused by deformation of crystal lattice near the impurity atoms. Therefore, additional distortions and free volume are formed along the boundaries. It is more expressed for carbon impurities. Moreover, with an increase in concentration of carbon in the metal, an increase in coefficient of grain-boundary self-diffusion was observed first, and then a decrease followed. This behavior is explained by formation of aggregates of carbon atoms at grain boundary, which leads to partial blocking of the boundary. Oxygen atoms had smaller effect on diffusion along the grain boundaries, which is apparently explained by absence of a tendency to form aggregates and lesser deformation of crystal lattice around impurity. The greatest effect of impurities on self-diffusion along the grain boundaries among the examined metals was observed for nickel. Nickel has the smallest lattice parameter, impurity atoms deform its lattice around itself more than aluminum and silver, and therefore they create relatively more lattice distortions in it and additional free volume along the grain boundaries, which lead to an increase in diffusion permeability. Diffusion coefficients along the high-angle boundaries with misorientation angle of 30° turned out to be approximately two times higher than along low-angle boundaries with a misorientation angle of 7°. Diffusion along the <100> grain boundaries flowed more intensively than along the <111> boundaries.

Type, relative concentration and size of most characteristic non-metallic inclusions for the elements of rails (head, web) from electro-steel of E79KhF and E90KhАF grades were determined on the basis of metallographic (with a microscope “OLYMPUS GX-51”) and spectral (using spectrometer “ARL iSpark” method “Spark-DAT”) analyses. It was found that the highest relative concentration of manganese sulfides (MnS) is 30.8 – 43.4 ppm. At the same time, 60 – 100 % of inclusions of this type are of small sizes (less than 4 μm), and it does not allow them to be detected using standard metallographic analysis with 100-fold magnification. The revealed high relative concentration of sulfide inclusions directly correlates with the established positive sulfur liquation in considered rail elements, which is up to 40 %. Despite the high concentration of manganese sulfides, their influence on the quality of rails can be considered not dangerous, taking into account their high ductility during hot deformation and the established prevalence of inclusions of this type with small size (less than 4 μm). Among inclusions of a silicate type, SiO₂ inclusions (3.4 – 14.9 ppm) have a significant concentration. All detected inclusions of this type have a size not exceeding 4 μm. It was found that the concentration of complex inclusions containing alumina (Al₂O₃ – CaO – MgO, Al₂O₃ – CaO – MgO – CaS, Al₂O₃ – CaO, Al₂O₃ – MgO) is insignificant: in total it does not exceed 3.1 ppm and 1.6 ppm for individual types. The concentration of corundum (Al₂O₃) is also insignificant and does not exceed 0.3 ppm. In this case, alumina inclusions of small size (less than 6 μm) prevail. Due to the low contamination (taking into account the relative concentration and size of inclusions) with non-plastic silicate and alumina non-metallic inclusions, their influence on the quality of the rails was not significant. It is confirmed by the absence of defects detected during ultrasonic testing.

A method for predicting the regularities of crystal growth from metastable melts has been developed. The process of crystal growth from a multicomponent melt is described by the methods of nonequilibrium thermodynamics, taking into account the mutual influence of thermal and diffusion processes. The application of a new variational approach to the constructed system of equations made it possible to obtain expressions of the crystal growth rate from a multicomponent melt convenient for practical calculations. The obtained technique allowed us to analyze the features of crystal growth at high rate of crystallization front, which leads to “impurity capture” effect – deviation from equilibrium conditions at the phase interface. The developed mathematical model makes it possible to calculate the growth rate of new phase particles and to estimate the effect of metastable effects on deviation of the components’ concentration at surface of the growing crystal from equilibrium values. Thus, using the obtained method, a “metastable” phase diagram of the system under study can be constructed. The developed approach is applied to the calculation of growth of α-Fe(Si) nanocrystals during annealing of amorphous alloy Fe_73,5 Cu₁ Nb₃ Si_13,5B₉. The calculation results were compared with the results of the experiment on the alloy primary crystallization. It is shown that the concentration of Fe at the surface of the growing crystal does not significantly deviate from the equilibrium values. On the other hand, silicon atoms are captured by the crystallization front, silicon concentration at the surface of the growing nanocrystal deviates significantly from equilibrium values. The calculation has shown that after the initial crystallization of the amorphous phase, occurring at a temperature of 400 – 450 °C, the deviation of silicon concentration from equilibrium value is about 2 %, while this equilibrium value is about 13.3 %.

In order to save resources of chromium, technology of flux-cored wire surfacing is of great practical interest. In this case Cr₂O₃ chromium oxide and carbon as a reducing agent are used as fillers. Thermodynamic assessment of probability of 16 reactions between them under standard conditions and for certain reactions under conditions different from standard was carried out using tabulated thermodynamic data of reactants in temperature range of 1500 – 3500 K. The following states were considered as standard states for reactants: Cr(ref) (reference state, melting point 2130 K, boiling point 2952 K), Cr(liq), Cr(gas), Cr₂O₃ (cr, liq), Cr₂O₃ (gas), C(ref), and as possible reaction products and standard states for them CO(gas), CO₂ (gas), Cr₂₃C₆ (сr), Cr₇C₃ (cr), Cr₃C₂ (cr). Probability of reactions was estimated using standard Gibbs energy and the Gibbs energy calculated using the Van Goff isotherm equation. Dissolution of chromium in metal of surfacing bath or probable partial pressures of CO and CO₂ in gas phase was taken into account and was calculated from equilibrium of carbon gasification reaction. Presence of carbon in flux-cored wire with chromium oxide Cr₂O₃ as a reducing agent will necessarily lead to occurrence of reduction reactions with generation of chromium carbides, and possibly chromium itself. Generation of Cr₇C₃ (сr) carbide is likely. With longer life time of chromium oxide and carbon at a temperature above 2500 K, generation of chromium as a component of the surfacing bath is more thermodynamically probable than generation of its carbides. Chromium oxide has the highest reactivity in Cr₂O₃ (liq) state. Direct reduction is preferential. Generation of CO(gas) as a product of carbon oxidation is more probable. Dissolution of chromium in metal increases thermodynamic probability of reactions with its generation and further reduces probability of reactions in which chromium is the starting material.

The model of ideal associated solutions was used for the analysis of thermodynamic properties of the Ca – Si – Fe melt. Chemical equilibrium, as per the law of mass conservation between associates and monomers in the assumed model version, was performed without consideration of mole fractions of these particles in solution but with consideration of the absolute number of their moles. It allows taking account the changes in the associated solution mole composition depending on the concentration of its components. The understudied binary sub-system Ca – Si was analyzed most comprehensively. Using the latest data of temperature dependency of heat capacity for five types of intermetallics of this sub-system, types of stable associates in it were defined, i.e. Са₂Si, СаSi in the solution range with low contents of silicon in solution and СаSi, СаSi₂ in the solution range with high contents of silicon in solution. Thermodynamic properties of the corresponding intermetallics in the databases Terra, Astra and HSC notably differ from the computed properties of the associates. The reason of disagreement of experimental and reference data consists apparently in the inaccurate reference information based on the previous underestimated studies of intermetallics’ heat capacities. Analysis of mixing energy of Ca – Si alloy components has shown that concentration and temperature dependencies of excessive free energy closely follow the so-called pseudosubregular model of binary solutions. Only two types of stable associates were defined for the other sub-system Fe – Si, i.e. Fe₃Si and FeSi. On the whole, energies of formation of these associates and respective intermetallics agree well. The third sub-system Ca – Fe was not considered because of the very limited mutual solubility of its components. Thus, only three associates, i.e. CaSi, CaSi₂ , FeSi, are valid out of five possible in the triple system Ca – Si – Fe in the range with high concentrations of silicon. A calculation under this condition of thermodynamic properties of calcium silicon melts for CK10 – CK30 grades has shown that activity of silicon in them at temperature 1873 K constituted 0.6 – 0.7, whereas activities of other components do not exceed 0.01.

In metal forming using high power current pulses, it becomes necessary to control both reproduction frequency and pulse amplitude. Description of a generator of high power current pulses with controlled thyristor converter is provided as a power source of charging device (charger) for regulating voltage (pulse amplitude) of capacitor charge. Faults of the generators associated with inrush current in capacitor charge modes are revealed, which reduces quality of supply network. To reduce time of transient processes while lowering voltage across capacitors, application of reverse thyristor converter is applied as a power source. Structural diagram of generator is considered, which includes reversible thyristor converter with separate control, power unit, capacitor recharge device, charger parameters automatic control system and capacitor charge process control system. Calculation of parameters of automatic control system regulators is presented. To obtain optimal transients, standard methodology for setting regulators to a modular optimum was used. In order to reduce overshoot at time of disturbances appearance, which can reach 100 % and higher, socalled logical device was introduced into the automatic control system. It blocks control pulses on thyristors of converter and simultaneously reduces signal at the output of current regulator to zero. Simulation model of high power current pulse generator in MatLab – Simulink environment was synthesized. Analysis of the model was carried out, and graphs are given that explain principle of device operation and transition processes under various operating modes. Generator application will allow user to adjust amplitude of current pulses with high speed and to obtain sufficiently high-quality transient processes of capacitors charge (discharge), which will have beneficial effect on supply network. Application of better converters will significantly increase frequency of reproduction of current pulses.

To assess operational reliability of technological units of continuous casting machine (CCM), quantitative indicator of efficiency has been applied. This indicator of efficiency describes ability of technical product to perform work assigned to it with a certain probability, or expectancy that this amount of work will be performed. This indicator is interesting for its optimal value, which being surpassed decreases machine ability to perform the necessary amount of work. Thus, the optimum point of machine operating time limits rational time portion of its use without repair with maximum efficiency. Workability of CCM as technological line as well as operability of its units was evaluated using statistical material obtained during the 15 years of operation of billet CCM. So, all units were divided into three essentially different groups according to conditions of their appointment, i.e. a group of units working with liquid metal, a group of units working with solidifying metal and a group of units working with solidified metal. Performance of each group of units is estimated in absolute and relative values. When assessing performance of CCM units in absolute values, units operating with liquid metal have the greatest performance. Its rational service life from repair to repair is 270 hours with reliability of 0.51. The smallest efficiency was manifested in units working with solidified metal. Its performance lasts 150 hours with reliability of 0.6. Average efficiency in relative units of all groups of aggregates is almost the same, which makes it possible to use this indicator at an early stage of assessing efficiency of both machine units and CCM as a whole.

The article considers a mathematical model of combustion zone of blast furnace working with the use of injection of coal-dust fuel. In this model, two subsystems were identified: 1) subsystem of heating the particles of coal dust and volatiles release in the combustion zone; 2) subsystem of heat exchange and combustion processes in the tuyere. A two-dimensional velocity field of gas in the combustion zone was investigated. The combustion processes are considered as a set of simultaneously developing phenomena of coke burning in a layer, single pieces of coke and particles of coal dust. The model includes following equations: total gas mass balance, gas component mass balance, gas heat balance, movement of coal dust particles and heat balance of coal dust particles. The model calculates maximum burning temperature in combustion zone; the distance from the cut of the tuyere to the focus of combustion; the length of the oxygen combustion zone; gas temperature; the content of gas phase components and the degree of carbon burnout of pulverized coal at the outlet of the tuyere combustion zone. Information-modeling system has been developed. It allows investigation of influence of combined blast characteristics, the properties of coke and coal-dust fuel, the geometric dimensions of tuyeres and other factors on temperature fields and concentrations of components of gas phase in combustion zone. The model also helps to select a rational mode of pulverized coal that will ensure completeness of its combustion in the tuyere combustion zone. Main functions of the program are as follows: representation of results of calculation in form of tables and diagrams, storage of options of basic data in a database and export of results of calculation to Microsoft Excel. Conclusions were made on reduction of combustion temperature in combustion zone and the approach of focus of combustion to the tuyere when pulverized coal was injected. The authors also have established the need to use coals with certain quality characteristics and place where coal dust was introduced into the blast stream.