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Vol 46, No 6 (2016)
- Year: 2016
- Articles: 13
- URL: https://journals.rcsi.science/0967-0912/issue/view/11108
Article
Microalloying and modification of steel with natural materials and industrial waste
Abstract
The use of natural materials and industrial waste in the microalloying and modification of steel is studied. The metallurgical properties of a natural barium–strontium modifier are investigated, and its influence on the melting point of reducing slag is assessed. The results show that its industrial use is very promising. Terra software is used to assess the reduction of barium and strontium from their oxides by silicon and aluminum. The action of barium and strontium on the metal quality is analyzed. The potential of vanadium converter slag in microalloying steel with vanadium is established. The effectiveness of carbon from molten steel in the reduction of vanadium is assessed. Industrial tests are in good agreement with the theoretical findings. Recommendations are made for the optimization of microalloying and modification. The use of the materials here investigated improves the economics of steel production and considerably enhances the quality of the steel produced. The prospects for expanded of use of natural materials and industrial waste are discussed.
373-377
Controlling the peripheral temperature of the blast furnace
Abstract
Increase in FeO content lowers the initial melting temperature of primary slags in the blast furnace and prevents the formation of stable surface coatings. That increases the thermal loads on the coolers in the bosh and bosh extension and correspondingly increases the heat losses. The FeO content in the primary slags is determined by the indirect reduction. In the present work, means of reducing the thermal loads on the coolers in the bosh and bosh extension are assessed. Decrease in the gas temperature at the furnace periphery is accompanied by change in the degree of indirect reduction. Hence, the peripheral temperature may be regarded as an indicator of the degree of indirect reduction. A model of the gas temperature and the reducing effect of the gas at the furnace periphery is developed and may be used to optimize the thermal state of the furnace shaft in the peripheral zone.
378-383
Oxidation of iron ore at moderate and high temperatures
Abstract
The oxidation of magnetite and titanomagnetites in iron-ore sinter at moderate (400–1000°C) and high (1000–1350°C) temperatures is subjected to physicochemical analysis. The oxidation kinetics is studied on briquets of Olkhovsk magnetite concentrate and Kachkanar titanomagnetite concentrate, as well as samples of unfluxed Kachkanar pellets and pellets fluxed to a basicity of 1.3. At moderate temperatures, the limiting stage in oxidation is the diffusion of the reagent to sections of the surface smaller than the total spherical surface. At high temperatures, in both isothermal and nonisothermal conditions, the limiting stage in oxidation is the diffusion of oxygen in pellet pores. From the kinetic equations for isothermal oxidation, the apparent activation energy with the specified degree of conversion is calculated; its variation is associated with change in the type of reagent diffusion through the layer of reduction products. The apparent diffusion coefficients of oxygen in Kachkanar pellets are determined at 500–1000°C. A method has been developed for determining the degree of pellet oxidation as a function of the time and the temperature in nonisothermal conditions. This method may be used to calculate the oxidation of the pellets in roasting on conveyer machines. The results may be used to determine the degree of oxidation in the roasted pellet bed and to optimize the heat-treatment parameters in roasting systems.
384-389
Losses of magnetite iron in wet separation
Abstract
Samples of all the tailings from enrichment processes at the Abagur plant operated by OAO Evrazruda are studied. The tailings are subjected to magnetic and chemical analysis, and the magnetic characteristics of the products are measured. The mean magnetite iron content in the tailings was about 0.9% in 2013. Experiments confirm that the main magnetite losses are associated with small classes and their poor magnetic properties. The losses of magnetite are reduced as the separation field is increased. At the plant, 45% of the barium–ferrite magnetic systems in the PBM 90/250 separators have been replaced by a system based on neodymium–iron–boron composites, with increase in the field from 111 to 175 kA/m. Modernization of the magnetic systems in all the separators at the Abagur plant is recommended. In thickening, the installation of separators for regeneration of the suspensions, with a field of 190 kA/m, is recommended. After reconstruction, the losses of magnetite iron at the plant may be reduced to 0.45–0.55%.
390-394
Operation of imported rail on the East Siberian Railroad
Abstract
Japanese R65 rail is metallographically analyzed after operation in the East Siberian Railroad. Its chemical composition complies with Technical Specifications TU 0921-239-01124323–2007 for the steel used in the production of 350LDT rail. The macrostructure of the metal is of satisfactory quality. The tensile mechanical properties, hardness, and impact strength at +20°C determined on samples from the nonoperational chamfer of the rail head are consistent with Technical Specifications TU 0921-239-01124323–2007 for the steel used in the production of 350LDT rail. The impact strength at negative temperatures does meet the corresponding requirements. The content of nonmetallic inclusions is low. However, exogenous inclusions are present at unacceptable levels. The microstructure of the Japanese rail sample consists of sorbite and plate pearlite, whose dispersity declines on moving away from the surface. In operation of the rail, thin inclined cracks (depth 1.1 mm) form at the surface of the working chamfer in the rail head; in addition, lateral wear is considerable (up to 15 mm).
395-400
Special boundaries in secondary recrystallization
Abstract
In polycrystalline Fe–3% Si alloy, various stages in low-temperature anomalous grain growth are investigated by electron backscatter diffraction (EBSD). For all the samples, the magnetic induction is relatively low: B800 = 1.62–1.72 T; that corresponds to deviation of the easy-magnetization axis [001] of the crystallites from the rolling direction by 12°–20°. The secondary-recrystallization texture is described by the orientations {110}<115>. The small grains between the anomalously growing crystallites (the secondary-recrystallization matrix) are characterized by strongly scattered (almost axial) texture {hkl}<001>. The orientation of the growing grains is close to disorientation Σ5 in most of the crystallites forming the absorbed matrix. The anomalously growing grains ultimately absorb crystallites with special boundaries Σ3 or Σ17b.
401-404
Rail strengthening in prolonged operation
Abstract
In rail operation (with traffic corresponding to passed tonnage of gross loads of 500 and 1000 million t), the surface layer of the steel is significantly strengthened. Electron-microscope data permit quantitative analysis of the contribution of different mechanisms to rail strengthening in prolonged operation, at different distances from the contact surface. The strengthening is multifactorial: it involves substructural strengthening associated with nanofragment formation; dispersional strengthening by carbide particles; the formation of atmospheres at dislocations; and polar stress due to interphase and intraphase boundaries. The significant increase in the surface strength of rail steel after prolonged operation (passed tonnage of gross loads of 1000 million t) is due to the presence of long-range internal stress fields and to the fragmentation of material with the formation of nanostructure.
405-409
Influence of reduction on the thermodynamic parameters of the gas flux in blast furnaces
Abstract
On the basis of operational data from three blast furnaces, the relation between the reduction processes and the thermodynamic parameters of the gas flux is established. Their influence on the mechanical energy is also determined. This relationship is due to mass-transfer processes resulting in the replacement of the light reducing gases CO and H2 by heavy CO2 and H2O. The mass-transfer processes, together with the temperature and pressure, increase the density gradient of the gas flux to 23.5–44.8 g/m3 m. That increases the force propelling the gas flux by 314.9–465.8 J/m3.
410-418
Metallurgical characteristics of unfluxed pellets produced from concentrates with different mineral content
Abstract
The metallurgical properties of roasted unfluxed pellets are studied as a function of the maximum roasting temperature, the proportions of silica introduced by silicates and quartz, and the quantity and composition of glassy silicate binder in the pellets. The mineral formation in the thermal strengthening of unfluxed pellets produced from concentrates with different mineral composition is analyzed. The microstructure of the final pellets is described.
419-427
Production of continuous-cast pipe blank without large nonmetallic inclusions
Abstract
The quality of metal in continuous-cast pipe blanks is investigated, for different steel-production technologies. The presence of large nonmetallic inclusions is largely due to disruptions in the continuouscasting technology. Other significant factors are nonoptimal modification of the nonmetallic inclusions and problems in ladle treatment. Measures ensuring acceptable content of nonmetallic inclusions are developed and tested.
428-434
Slag conditions in electrosmelting: A review
Abstract
The literature on the foaming of electrofurnace slag is reviewed. On that basis, recommendations for improvement in slag foaming are formulated. Inconsistencies in the published data are noted, and some principles are elaborated. It is evident that two key factors have been ignored in the existing research: the temperature of the slag; and its content of small gas bubbles.
435-442
Shaping of sheet to produce large-diameter welded pipe
Abstract
The quality of welded pipe (diameter 508–1420 mm; wall thickness 8–48 mm) of strength class up to K80 (X100) is investigated. Plastic shaping is simulated, with quantitative estimation of the stress–strain state of thick-walled pipe blanks in TESA 1420 presses during edge bending and stepwise shaping. The corresponding computer program permits calculation of the setup of the equipment and determination of the geometric parameters of the pipe blank specified in the standards. Theoretical results are presented for a range of large-diameter pipe produced on the TESA 1420 system.
443-446
Role of evaporation in the formation of smelting dust
Abstract
The role of evaporation and dispersion in the formation of smelting dust is considered. A mathematical model is proposed for the evaporative generation of dust when working molten metal. It is compared with experimental data. The main factor affecting the mass of dust formed and the dimension of the dust particles is the surface temperature of the melt. Increase in that temperature increases dust emission, and the particle diameter is greater. The size of the smelting-dust particles is considerably increased on coagulation: at liquid drops or in electrostatic, magnetic, and acoustic fields.
447-452