Vol 47, No 10 (2017)

In the straightening of steel sheet, it is necessary to calculate the optimal reduction of the steel blank by the working rollers of the straightening machine so that the sheet produced has the minimum residual stress and curvature. In the simulation of sheet straightening in multiroller machines, the curvature and bending torques of the steel sheet at contact points with the working rollers are first calculated and then the straightening forces are determined. In straightening steel sheet, it is important to calculate the forces in the multiroller straightening machine. Such calculations are based on determination of the reaction of the roller bearings and the forces at the upper and lower working-roller cassettes in straightening. With insufficient bending torque, it is impossible to eliminate harmful residual stress and surface defects in the sheet. Extreme roller torques and forces at the roller cassettes often lead to defects of the sheet, fracture of the working and supporting rollers, and failure of the straightening machine. In the present work, an approximate method is proposed for calculation of the optimal cold-straightening parameters of the steel sheet in a multiroller machine. The calculations permit determination of the curvature of the neutral plane in the sheet on straightening, the residual curvature of the sheet after straightening, the bending torque and the reaction of the working-roller bearings, the residual stress in the sheet, the penetration of the plastic deformation into the depth of the steel sheet, and the relative deformation of the longitudinal surface fibers of the sheet on straightening as a function of the radius of the working rollers, the distance between the rollers of the straightening machine, the reduction of the sheet by the upper rollers, the sheet thickness, and its properties (Young’s modulus, yield point, and strengthening modulus). The results may be widely used at manufacturing and metallurgical plants.

Thermodynamic analysis is applied to the physicochemical processes in the converter bath when intensifying bath heating by means of gas–oxygen burners. In the converter’s working space, when the combustion flames interact with the liquid bath, the oxygen and natural gas supplied through the burners and the oxygen supplied through the tuyere interact in a bubbling slag–metal emulsion. As a result, iron and the impurities are oxidized. The use of such burners changes the gas composition: not only O₂, CO, and CO₂ are present, but also H₂ and H₂O, which changes the oxidative capacity of the gas phase. The presence of solid carbon (for example, pulverized coal) in the burner flame may be used to control and intensify the combustion process. Combustion is most effective in the oxidation of carbon to CO when the oxygen excess is less than 1.0. The oxidation conditions of carbon in the melt change with variation in its activity as a function of its concentration and the temperature. The equilibrium in the M–O–C system may be described by the oxygen partial pressure \({P_{{O_2}}}\), which may be regarded as a universal characteristic. In addition, the equilibrium may be assessed on the basis of the associated ratios \({P_{CO}}/{P_{C{O_2}}}\) and \({P_{{H_2}}}/{P_{{H_2}O}}\) It is found that iron may be oxidized by oxygen and, to some extent, by carbon dioxide. At 1600–2000 K, there is practically no oxidation of iron by steam. The carbon dissolved in the steel is oxidized relatively effectively by oxygen and carbon dioxide until its concentration is less than 0.1% C. Steam oxidizes carbon very poorly and is not much more effective with manganese and silicon. With increase in temperature, the rate at which carbon dissolved in steel is oxidized by oxygen increases, while the oxidation rate of manganese and silicon falls. Above 1800 K, superoxidized slag with a high FeO content actively oxidizes silicon (to <2% Si), manganese (to <1% Mn), and carbon (to <1.5% C).

The development of Chernov–Luders bands on elastoplastic transition in low-carbon steel is investigated. The main factors responsible for the creation and development of the bands are identified. The kinetics of the mobile band boundaries (fronts) is of particular interest. The characteristic speeds are determined. The nucleation rate of Chernov–Luders bands exceeds their expansion rate by more than an order of magnitude. The simultaneous development of more than one band, with the appearance of several moving fronts, is considered. In all cases, the fronts of the Chernov–Luders bands move at matched speeds, so that, at any time, the generalized expansion rate of the deformation zone is constant. The influence of the strain rate on the kinetics of the band fronts is analyzed. Both the generalized expansion rate of the deformed zone and the speeds of individual fronts increase with increase in the loading rate. This is a nonlinear dependence (a power law). The fronts of the Chernov–Luders bands are complex in structure. Different sections of the front may move at nonuniform speeds, so that the front is locally distorted and split. Ahead of the front, in the undeformed sample, precursors whose configuration resembles that of the incipient Chernov–Luders bands may be observed. When they meet, the fronts of adjacent bands cancel out. Annihilation of the band fronts is a complex process, characterized by the formation of precursors and secondary diffuse Chernov–Luders bands. These findings indicate that the simplified concept of the Chernov–Luders bands as a deformed region in a loaded sample, as the front of a band, or as the boundary between deformed and undeformed zones must be revised. A microscopic theory of Luders deformation is based on the cascade growth in density of mobile dislocations on account of their breakaway from the points of attachment and their subsequent multiplication, which occurs instantaneously at the upper yield point within the crystallite (grain). At the same time, the formation of a mobile macroscopic strain front calls for the transfer of plastic deformation by adjacent grains, without strengthening. In other words, grain-boundary accommodation is required. The results obtained suggest that the Chernov–Luders band is such an accommodation zone, and so it has a complex structure.

Numerous problems are encountered in the introduction of pulverized-coal injection at a 5000-m³ blast furnace. To resolve those problems, changes are proposed in the furnace profile, the number and diameter of the air tuyeres, the batch distribution in the mouth, and the gas flux in the hearth.

The creation of a new class of carbon reducing agents containing 40–95% carborundum is considered. The carbon is derived from a wide range of natural and industrial materials, including mill siftings, coke, semicoke, high-ash coal, and coal-enrichment wastes. By two-stage production—first of carborundum-bearing reducing agents and then of high-silicon alloys—the range of possible raw materials may be markedly expanded, and the costs of materials and energy in alloy production may be significantly reduced.

By means of DEFORM-2 software, cold rolling with vibration of the working rollers is simulated. It is found that self-oscillation significantly affects the fluctuation of the longitudinal stress in the metal and the rolling forces in adjacent stands of the continuous mill; and only slightly affects the longitudinal thickness variation of the strip. That leads to deviations in the surface profile.