Том 49, № 8 (2019)

The methods of microgeometry formation for the surface of temper mills rolls are presented providing the required roughness of the cold rolled strip. It was established that with the electroerosion processing a more uniform structure is formed on the roll surface with a smoothly changing microrelief, compared with the mechanical action of the abrasive. The most effective abrasive for the microrelief formation on the rolls surface is cast and split steel shot. The process of interaction predominantly occurs with a round-shaped shot, since the sharp edges of the split shot also become blunt during the process. In the present work, the microdepression of the roll is approximated by a spherical shape. A model of roll roughness transfer to the strip was developed taking into account the type of roll processing and tempering conditions, which makes it possible to evaluate the degree of filling of a single microdepression relief at known pressures at contact of the strip with the roller, friction coefficient, roll roughness parameters and tempering modes. A quantitative estimation of reproduction of the roll roughness on the tempered strip was obtained, characterized by the roughness ratio, which is the ratio of the depth of the metal flow into the strip microdepression to the depth of the roll spherical microdepression. Determination of the dimensionless pressure requiring the flowing of a deformable metal into it was performed using the superposition method for meridian sections in two mutually perpendicular planes. The reproduction dependencies of the micro-geometry of a temper mill roll on a rolled strip on the shot size, tension, and the height parameter of roughness are presented during the tempering of stripes with various thickness, which can be used to simulate the transfer of the roll micro-relief to the rolled strip.

By using the methods of modern physical material science, the structure-phase states and properties of the layers formed on low-alloyed steel Hardox 450 with the use of welding wires with a boron content amounting to 4.5 and 6.5 wt % have been analyzed. In the initial state, steel Hardox 450 has the structure of tempered martensite in the bulk and along the boundaries of crystals in which cementite particles are located. The particles located in the bulk are needle-shaped and those located along boundaries are mainly round-shaped. The revealed extinction bend contours indicate a torsion curvature of the crystal lattice in this area of the material. They begin and finish at the interfaces of the martensite crystals. The scalar density of chaotically arranged dislocations forming a reticulate-type substructure is 6.2 × 10¹⁰ cm^–2. The weld-deposited layer onto steel Hardox 450 has more than two-fold microhardness than that of the base metal. The analysis of state diagrams for the Fe–C, Fe–B, and B–C systems and of polythermal cross-sections in the Fe–C–B system has shown that a rapid cooling of Fe₂₃C₆–Fe₂₃B₆ alloys from the liquid state facilitates the formation of multiphase structural states. It has been established by means of transmission electron diffraction microscopy that the reasons for the high microhardness level of the surface layers consist in the following factors: the formation of iron borides and the crystals of ultrafine packet martensite (up to 100 nm) having a high level (~10¹¹ cm^–2) of scalar dislocation density; the presence of nanosized particles of iron and boron carbides in the bulk and along the boundaries of martensite crystals; and a high torsion curvature level in the crystal lattice of iron borides and α-phase grains caused by internal stress fields along interphase boundaries (the interface between iron boride crystals and α-phase grains) and intraphase boundaries (the interface between iron borides and martensite crystals in the packet). Increasing boron concentration from 4.5 to 6.5% is accompanied by a sufficient (1.2–1.5-fold) increase in the hardness of the weld-deposited layer. It is caused by a 1.5–2.0-fold increase in the size and relative content of iron boride areas.

In this paper, we studied the interaction of magnesium and aluminum dissolved in liquid iron with oxygen, which is an important problem for choosing the optimal parameters of steel refining and casting. The relevance of the study is determined by the possibility and conditions for the formation of adverse refractory particles of magnesium oxide and magnesian spinel in the melt. We performed the thermodynamic modeling of phase equilibria realized in the liquid metal of the Fe–Mg–O, Fe–Al–O, and Fe–Mg–Al–O systems in the temperature range of 1550–1650°C. The calculation was carried out using a technique for constructing the surface of the component solubility in a metal, which associates quantitative changes in the liquid metal composition with changes in the composition of the interaction products of molten metal components. The modeling method was based both on the use of equilibrium constants of reactions occurring between the components of the studied systems in the selected temperature range and on the account of the values ​​of the first-order interaction parameters (according to Wagner) of elements in liquid iron. To simulate the activities of an oxide melt conjugated with a metal melt, the approximation of the theory of subregular ionic solutions was used. The approximation of the theory of regular ionic solutions was used to model the activity of a solid solution of oxides while the theory of perfect ionic solutions was used to model the activity of a solid solution of spinels. The isotherms of oxygen solubility in the liquid metal of the Fe–Mg–O, Fe–Al–O, and Fe–Mg–Al–O systems were plotted, and the regions of thermodynamic stability of oxide phases conjugated with the metal melt were determined. In particular, for the Fe–Mg–Al–O system, the region of liquid metal compositions, in equilibrium with which there will be a solid solution of spinels |FeAl₂O₄, MgAl₂O₄|_ss, was determined. The obtained results of thermodynamic modeling are compared with experimental data.

The drop in static gas pressure in the blast furnace is not equal to the pressure loss of the gas flux over its path from the tuyere to the furnace mouth. The Darcy–Weisbach or analogous equations cannot provide the theoretical basis in studying the blast furnace’s gas dynamics. The pressure loss of the gas flux over its path from the tuyere to the furnace mouth is better described by the Clapeyron–Mendeleev equation, which relates directly to the physical character of the pressure.

The tension modes of cold-rolled strip coiling are analyzed. The dependences of the stress-strain state of the coils on the strain degree, temperature, velocity, strip rolls surface roughness during cold strip rolling are considered. Coiling methods provide improvement of production efficiency and the quality of cold-rolled sheet steel by preventing the appearance of such rolling defects as bent fractures and coil shape defects.

The multiple regression analysis method is used for quantitative estimation of the complex of factors affecting the mechanical properties of the thermomechanically strengthened rebars; this method permits selecting the most valuable quantities characterizing σ_y, σ_uts, and δ and assessing the degree of influence of separate elements on these properties within the standards and technological parameters of strengthening. A mathematical model of formation of the strength and plastic characteristics of thermomechanically strengthened rebars is developed, which allows predicting their final mechanical properties. The analysis of the derived relations shows that the established character of the dependences, determined by the signs of coefficients, responds to the physical meaning of a technological factor at consideration.