Steel in Translation

The 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 the molecular dynamics method. Ni, Ag, and Al were considered as metals. Metal atom interaction was described by many particle Clery-Rosato potentials constructed within the framework of tight binding model. To describe interactions of light-element impurity atoms with metal atoms and impurity atoms, 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 crystal lattice deformation near the impurity atoms. Therefore, additional distortions and free volume are formed along the boundaries, which is more expressed for carbon impurities. Moreover, with an increase in carbon concentration in the metal, an increase in coefficient of grain-boundary self-diffusion was observed first, and then followed by a decrease. This behavior is explained by aggregate formation 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 the absence of aggregates and lesser deformation of crystal lattice forming around impurity. The greatest impurity effect on self-diffusion along the grain boundaries among the examined metals was observed for nickel. Nickel has the smallest lattice parameter, and impurity atoms deform its lattice around itself more than aluminum and silver. 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.

A technique is developed for predicting the patterns of crystal growth from metastable melts. Using nonequilibrium thermodynamics methods, a crystal growth process from a multicomponent melt is described, which considers the interaction between thermal and diffusion processes. The application of a new variation approach to the constructed equation system has made it possible to obtain expressions for the crystal growth rate from a multicomponent melt, which is convenient for practical calculations. The developed technique has made it possible to analyze the crystal growth features at a high motion speed of the crystallization front, which leads to an “impurity capture” effect, i.e., the deviation from the equilibrium conditions at the interface. The developed mathematical model makes it possible to: calculate the growth rate of new phase particles, as well as evaluate the influence of metastable effects upon the deviation of component concentrations near the growing crystal’s surface from equilibrium values. Thus, with the use of the developed method, a “metastable” phase diagram of the system under study can be constructed. The approach under development has been applied to the calculation of the α-Fe(Si) nanocrystal growth in the course of the annealing of amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy. The calculation results are compared with the experiment results on the alloy’s primary crystallization. It has been shown that the iron concentration at the growing crystal’s surface insignificantly deviates from the equilibrium values. On the other hand, silicon atoms are captured by the crystallization front; the silicon concentration at the growing nanocrystal’s surface significantly deviates from the equilibrium values. After the primary crystallization of the amorphous phase occurring in the temperature range from 400 to 450°C, calculations show that the silicon concentration’s deviation from the equilibrium value should be about 2%, whereas the equilibrium concentration value amounts to about 13.3%.

In metal processing by powerful current pulses, there is a need for adjustment of both the pulse repetition rate and amplitude. This paper describes a powerful current-pulse generator with a controlled thyristor converter, which is used as a power source for a charging device for regulating the voltage (pulse amplitude) of a capacitor charge. The disadvantages of the generators associated with the current spike in the capacitor charge modes that reduces the supply network quality are discussed. The application of a reverse thyristor converter (RTC) as a power supply is considered to reduce the transient time at a voltage decrease on the capacitors. The generator’s structural diagram that consists of a reversible thyristor converter with separate control, a power unit, a capacitor recharge device, an automatic control system (ACS) for the charger parameters, and a capacitor charging control system is presented. The regulator parameters of the ACS are calculated. To obtain optimal transients, a standard methodology for regulator tuning according to a modular optimum is employed. In order to reduce overadjustment at the disturbance time reaching 100% and higher, the so-called logical device is introduced into the ACS. The latter blocks the control pulses on the converter thyristors and simultaneously reduces the signal at the output of the current regulator to zero. A simulation model of a powerful current pulse generator is synthesized in the MatLab-Simulink environment. The model is analyzed, and plots explaining the device’s operation principle and transients in various operating modes are shown. The use of a generator will allow high-performance adjustments of the current pulse amplitude and obtain sufficiently high-quality capacitor charge (discharge) transients, which will have a beneficial effect on the power supply network. The application of higher quality converters will significantly increase the current pulse repetition rate.

This paper shows that the existing siderite ore preparation techniques do not allow achieving high blast-furnace smelting levels as compared with using black iron ore concentrates with a high iron content. To make blast-furnace smelting more efficient, it is necessary to use the metallized product made by regenerative siderite ore roasting. The technology developed for this roasting allows producing metallized concentrate with a Fe content of 65–68%. The main provisions of regenerative siderite ore roasting in shaft furnaces are formulated, and the three-zone shaft furnace design proposed for implementing this process. The thermal and consumption parameters of the process are provided as well as the lean gas circuit of regenerative ore roasting. This circuit allows significant cutting the expenses. The metallized siderite ore product with a high iron content allows gaining major economic benefits in blast-furnace production.

This article discusses possible approaches to increase the capacity of a finishing train using strip rolling with an inverse temperature wedge. One calendar year of operation of a continuous wide-strip hot-rolling mill (NShSGP) is considered. Analysis of plant data demonstrated that the rolling time is by 7–10% lower in the case of rolling with an inverse temperature wedge, which allows increasing overall mill capacity. The obtained results can be applied during rolling of low carbon steels for cold pressing, and their fraction in mill production prevails; thus, it is possible to significantly increase mill capacity without making additional capital investments.

The article considers the nature, occurrence mechanism and development of resonant vibrations found in the working stand equipment of cold rolling mills during the production of strips with a thickness of 0.4–0.6 mm at speeds of more than 12 m/s. Vibration causes are possibly based on changes in the metal properties during rolling due to acquired hardening and forming of internal friction peaks.

This paper provides data about modern alloys with specific physical properties (precision alloys). The following aspects are provided and described: classification of these alloys, physical ways in which their properties are formed, and the main parts of their production technology. Several promising areas for creating new precision alloys with complex combinations of performance properties are considered.