Vol 48, No 12 (2018)

The production efficiency in steelmaking may be increased by decreasing the consumption of scarce and expensive ferroalloys. One possibility here is direct alloying of steel with oxides. In the present work, the direct alloying of steel with manganese oxides (manganese ore) is thermodynamically analyzed and tested industrially. Two technologies are considered: alloying in oxidative conditions with smelting of the steel in a 100-t electrosmelting furnace; and alloying in reductive conditions with treatment of the steel in a ladle–furnace unit. Thermodynamic modeling of the oxidative technology by means of Astra software shows that the manganese content in the steel may be increased by introducing manganese ore. A determining factor here is the carbon content in the steel. For steel with moderate or high carbon content, the manganese content may be increased to 0.6% or more. For low-carbon steel, the residual manganese content depends on the carbon content at the end of oxygen injection. The corresponding graph is plotted. In the reductive technology, the main reaction in direct alloying is MnO + Si = Mn + SiO₂. Thermodynamic analysis yields relatively approximate data. Therefore, a semiempirical analysis is adopted, on the basis of data from experimental tests on the FeO/MnO ratio in the slag at the end of steel treatment in the ladle–furnace unit. This approach is possible since the metal–slag system approaches equilibrium on prolonged treatment in the ladle–furnace unit. On the basis of the FeO/MnO ratio, as well as the assumptions that the initial slag basicity is retained and that the FeO content in the slag is maintained at around 1%, a balance equation is written, describing the direct alloying of the steel by manganese ore in the ladle. The balance equation permits calculation of the primary technological parameters of direct alloying by manganese ore in production conditions. The agreement of the theoretical calculations and industrial data is good.

The production of a solid-phase diffusion bond in OT4-1 alloy on the basis of a cold forced fit of components in a shaft–hole configuration is considered. The influence of the maximum stress–strain state in the cold forced fit and subsequent heat treatment (in autonomous vacuum) on the structural evolution and properties of the contact region is investigated. In cold plastic deformation of the alloy with the formation of a solid-phase diffusion bond, deformational relief (traces of grain-boundary slip) is observed in the microstructure of the contact region. In addition, decrease is noted in the area of the contact surfaces, and fewer bulk interactions are noted in the contact plane (grain distortion) and in the contact volume (regions of dislocation departure). The basic characteristics of the structural interface—the unit parameter of structural organization, the grain density, the mean grain-boundary density, and the development of the grain boundaries—exceed by factors of 10, 4, 1.8, and 1.5, respectively, those of the basic metal in the initial state. Heating in autonomous vacuum in the range of α → β phase transitions leads to stepwise structural changes in the basic metal and in the contact region of the solid-phase diffusion bond. Initially, a globular component appears in the microstructure. With further heating, this component reverts to the initial acicular structure (with some increase in microhardness). The formation of globular structure on heating plastically deformed metal is observed not only at temperatures corresponding to phase transition but also at higher temperatures; this has not previously been noted. With increase in temperature, the duration of this stage decreases. In addition, with less developed plastic deformation, the formation of globular structure is observed close to the polymorphic-transformation temperature T_pt, with shorter holding. For the basic metal (with little deformation), the globular structure disappears practically completely after heating for 10 min at 950°C. In the cold-deformed contact region of the solid-phase diffusion bond, the globular structure disappears on heating for 1 h at 950°C, for 40 min at 975°C, and for 20 min at 1000°C. At those temperatures the sealing of discontinuities is practically complete. In other words, the weld line disappears: the metal with continuous microstructure in the contact region does not differ from the basic metal, except for a slight enlargement of the microstructure. Quantitative assessment of the structural changes in terms of the basic characteristics of the structural interface permits determination of their mechanism and kinetics and also the dependence of the structure on the plastic strain and the heat treatment. On that basis, it is possible to identify conditions such that the discontinuities are eliminated, the boundaries disappear, and the properties of the solid-phase diffusion bond are no worse than those of the basic metal.

In a microplot field trial, the use of crushed slag to break down the capillary borders in recultivation of toxic tailings (at enrichment facilities and solid waste dumps) with minimum application of fertile soil was studied. In this approach, metallurgical wastes may be used in low-cost energy-saving technologies. Four basic types of slag produced at AO EVRAZ ZSMK in steel smelting were studied: white nonferrous slag; blast-furnace (open-hearth) slag; electrosmelting slag; and converter slag. Such slag forms an inert layer under a minimal layer of fertile soil on trial plots, where perennials (a legume–grass mixture) were planted. For each slag, we used a control plot (without fertilizer); a plot with a potassium-humate preparation; a plot with complete mineral fertilizer; and a plot with a mixture of these approaches. At the end of the growing season, the above-ground phytomass is 17–128 g/m². The best results were obtained with converter slag and blast-furnace slag, characterized by the lowest phytoxicity. Addition of mineral fertilizer alone or in combination with potassium humate increases the phytomass by a factor of 2–4. Added alone, potassium humate had no influence on plant production but, in combination with mineral fertilizer, it increased the phytomass by a factor of 1.6–1.8. To stimulate germination and phytomass production, the addition of both mineral fertilizers and humic preparations is recommended. The converter and blast-furnace slag may be used as an inert material in reclamation, with minimum application of fertile soil. White slag and electrosmelting slag are not recommended, on account of their high phytotoxicity; in those trials, the perennials employed did not thrive.

For blast furnaces equipped with bell-less and bell-type charging systems, the optimal ranges of the characteristics K₁–K₄ of the gas-flux distribution are established for different gas-dynamic conditions and different fuels. An expert module has been developed for the system monitoring the temperature of the gas flux above the batch surface in controlling the charge at two blast furnaces. Tests of the module prove successful.

For a coil of rolled C86D steel subjected to accelerated continuous cooling from the hot-deformation temperatures, change in austenite grain size by scores no greater than 1–2 according to State Standard GOST 5639–82 has no significant influence on the impact strength. For C86D steel, the impact strength is directly related to the extent of the ferrite–cementite phase boundaries: the impact strength increases with increase in the boundary length. These results are of practical interest in developing new alloys and conditions of deformation and heat treatment for high-strength pearlitic steels.

The quality of structural steels currently available is discussed. Their characteristics are regulated by new standards for steel and iron structural components and in design standards. Such components include beams, pipes, and rolled components for use in buildings, bridges, and other structures. The maintenance of high performance in high-strength steels is considered. The feasibility of decreasing factors such as the cost of metal structures and the manufacturing complexity is discussed. The excellent cold strength of current steels permits improvement in the operational reliability of structures, especially in the severe climatic conditions encountered in Siberia and in the Arctic.