Vol 49, No 9 (2019)

The intended form of relatively flexible cylindrical parts (shafts and axles) may be restored by straightening by flexure under a distributed load, with subsequent strengthening of the workpiece by surface plastic deformation based on transverse rolling between flat plates. It is well known that the nonequilibrium stresses are generated in the whole workpiece after straightening by transverse flexure, and the part is eventually deformed again. Therefore, the workpieces should be additionally straightened with surface plastic deformation after straightening by flexure. We use transverse rolling by flat plates for that purpose. The aim in the present work is to determine the capture conditions and the stress state of the workpiece in transverse rolling of cylindrical parts between flat plates. The mathematical analysis is based on the theory of an elastoplastic solid; ANSYS Workbench software is employed. A new method is proposed for control of stress state in straightening of cylinderical workpieces. The limiting capture angle α ranging 2–8 degrees and the maximum absolute reduction depending on friction coefficient and on the diameter of workpiece are obtained. The optimum reduction varies ΔH = 0.07–0.15 mm. The calculation data show that the stress state of uniform extension occurs at the center in the workpiece cross section after transverse rolling, and the stress state of reduction is formed at the peripheral areas of the workpiece. The straightening method of transverse rolling between flat plates eliminates crack formation and destruction of the material in the central area of the cylindrical parts.

A thermodynamic analysis of carbon gasification process in the presence of moisture has been performed. The chemical process has been represented by system C–O–H with a ratio between the elements therein amounting to 1 : 1 : 2 and 1 : 2 : 2. To refine the methodology of the studies and to verify the results, a well-studied C–O subsystem has been used. The initial array of the processed data has been represented by a content of such chemical components as C, CO, CO₂, CH₄, H₂, and H₂O calculated using a Terra software package. There is no unit chemical reaction in the С–О–Н system; therefore, the entire operating temperature range from 298 to 1400 K has been divided into three characteristic subranges to analyze each of them separately. By comparing the numerical values of component content at the boundaries of the subranges, a change in the values going from one subrange to another has been determined. These values are multiples of stoichiometric coefficients for the proposed chemical reactions. Thus, the problem of establishing the type of chemical reactions has been solved. However, in two of the three subranges, the identified reactions exhibit a complicated character, that is, they contain more than four components. Therefore, we have decomposed them in the basis of three more simple reactions inherent in these thermal subranges. As a result, the total number of reaction types has been reduced to four: two main reactions of carbon gasification (С + 2H₂О = СО₂ + 2H₂, С + СО₂ = 2СО) and two reactions of methane formation and decomposition (2С + 2H₂О = СН₄ + СО₂, СН₄ = С + 2H₂). At the same time, with the use of balance coefficients β, the fraction of each reaction in the general chemical process has been determined. However, the type of chemical reactions gives all the necessary information concerning the content of system components only at the boundaries of the subranges. The quantitative assessment of the chemical process in the temperature subranges can be obtained by determining the temperature dependence of the reaction coordinates ξ(Т) as a function of Gibbs energies and pressure, i.e., ξ(Т) = f [Δ_rG°(T), Р]. The reaction coordinates ξ in combination with balance coefficients β make it possible to calculate not only the content of the reactants and reaction products, but also the conditional temperature values for the beginning and termination of the reactions themselves. In this case, no fitting coefficients and parameters of a fitting should be used in the calculations. The average absolute error in the quantitative description of computer simulation results for system C–O–H is less than 0.02 mol (per 1 mol of carbon), whereas for subsystem C–O it is almost zero.

The problem of dephosphorization of iron-carbon alloys is relevant for the metallurgical industry, since a high concentration of phosphorus contributes to the appearance of a number of extremely undesirable phenomena. A lot of experimental work has been devoted to solving this problem, but it has still not been completely possible to cope with it. Any field experiments aimed at studying the process of phosphorus removal require considerable material and time costs, but at the same time do not guarantee getting the desired result. Therefore, to search for new approaches to solving this problem, it is much more rational to use numerical simulation methods involving the computational capabilities of modern computers. At present, computer experiments are the same recognized research method as theoretical research and real experiment. To study the behavior of phosphorus atoms in iron using a numerical experiment, it is necessary to build a computational model and test it by calculating various characteristics whose values are known in advance. In this paper, the method of molecular dynamics was chosen as the method of computer simulation. Using this method, one can conduct experiments with given atomic velocities and describe dynamics of the studied processes. To describe the interparticle interaction, we used the potential calculated in the framework of the immersed atom method. The study was conducted on a computational cell simulating α-iron crystal with phosphorus substitution atoms. The constructed model demonstrated satisfactory results when calculating the known characteristics of the simulated system. Dependencies of changes in such characteristics as temperature coefficient of linear expansion, melting point, latent heat of melting and heat capacity on the concentration of phosphorus atoms, as well as in some cases on magnitude of the applied external pressure, were established. Calculations showed that, for example, the phosphorus concentration of 0.5% leads to an increase in the average thermal coefficient of linear expansion by 9%, a decrease in temperature and latent heat of fusion by 5% and a heat capacity by 7%.

The cluster analysis of burden surface temperature and plotting graphs, in which nodes are predicted states and edges are a type and weight of filled materials, is a control tool of the blast furnace operation. The control of material charge aiming for a high efficiency of furnace operation (high yield of cast iron, t/day, low specific energy consumption) is maintained by predicted adjustments of weight or filling frequency on the basis of cycles in graphs with the highest ore charge. The proposed control methods make it possible to maintain efficient operation modes of furnace, to increase ore charges, and to decrease specific coke consumption by 4%.

This paper presents the results of the metallographic study of the structural condition of metal in the billet after soft reduction. The billet is deformed in the withdrawal and straightening unit of the continuous casting production line when there is an uncrystallized core area in the bullet. The reduction takes place due to the movement of the top driven roll. The metallographic studies reveal the crack initiation characteristics when an external deformative action is applied in the course of incomplete crystallization of continuously cast billet. They provide a well-reasoned approach to selection of techniques minimizing the number of initiation centers.

The research results of the nitrogen and vanadium influence on the microstructure, fine structure formation and mechanical properties of low-carbon steel pipe are considered. It is shown that it is possible to obtain cold-resistant mill products with strength classes from K48 to K60 with high (26–29%) percentage of elongation by dispersion hardening due to the precipitation of vanadium particles together with hardening of a manganese solid solution in the conditions of the Vyksa Metallurgical Plant casting and rolling complex.