Metallurgist最新文献

The article analyzes the results of studying a promising method for obtaining functionally graded 3D materials based on the use of the “cold” gas-dynamic mono-powder spraying technology in a separate dispenser system. In particular, for Al–Al₂O₃ composite, the effect of the ceramic component content on the coefficient of linear thermal expansion was determined. The study results can be used when designing and creating materials operating in thermally-stressed assemblies to reduce stresses by adjusting thermal gaps. The obtained data highlight the advantages of the “cold” spraying method as a progressive way to create 3D metal and metal-ceramic materials with a functionally graded structure. Future development of these findings requires further scientific and technical justification.

Comprehensive studies of five varieties of hot-rolled microalloyed steels with different chemical compositions were conducted. The influence of structural characteristics of steel on its corrosion resistance was assessed. It was shown that the greatest contribution to the increase in corrosion resistance of steel is made by the chromium content; its increase to 0.5–0.6 wt. % raises the corrosion resistance of steel by 2 times. The high density of nanosized interphase precipitates of carbides and carbonitrides of microalloying elements, such as vanadium and niobium, leads to a decrease in corrosion resistance of steel, while the reduction of corrosion resistance of steel because of the presence of non-metallic inclusions of unfavorable composition is significantly lower.

In this study, the elemental composition of dust from the melting of scrap metal in an electric arc furnace was analyzed using an X‑ray fluorescence energy dispersive spectrometer (RLP-21) to determine the concentrations of impurities at their lower detection limits. A wide range of impurities was identified in the dust: Cu, Fe, Ti, Cr, Ni, Cd, Mn, Sn, Si, Ca, K, S, Cl. Using the Olympus BX51 microscope, new data on the forms of impurities in dust have been obtained. It was shown that impurities in the dust are present in the form of oxides. Based on the new results, a thermodynamic analysis of the reactions between dust components and ammonium chloride under low-temperature sintering conditions (573–1073 K) was performed. It was found that almost all impurities, except chromium, concentrate in the clinker as solid oxides during the sintering process. A high potential for the removal of titanium and tin as gaseous chlorides in the vapor phase was identified. Laboratory experiments were conducted on sintering dust with NH4Cl under optimal process conditions (temperature—773 K, NH₄Cl consumption—1.5 times the stoichiometric amount required for lead chlorination, sintering time—60 min). Based on these experiments, the quantitative proportions of impurities in the resulting clinker were determined. It was found that during sintering tin and titanium are volatilized in significant amounts (more than 30% of their total content in the initial dust). The results obtained are fundamental for the development of selective lead extraction technology from dust. They will be used to develop an integrated chlorination process for the treatment of ironmaking dust with selective recovery of valuable metals into marketable products.

The main mechanisms of carbon removal from the melt during circulation vacuum treatment have been identified. It has been shown that, at the initial stage of metal processing, the primary mechanism of decarburization is the formation of CO gas bubbles within the melt. As the carbon concentration decreases, the dominant mechanism shifts to carbon removal through gas injection. To achieve low carbon concentrations (below 0.002%), it is necessary to intensify the mechanisms of carbon removal and reduce the amount of carbon dissolving carbon from the lining of the steelmaking unit.

The effect of iron and silicon impurities on the phase composition and hardening of Al‑0.3Zr-REM (REM = Er, Y, Yb or Gd) alloy ingots during annealing was studied. The Al₃Fe phase was observed in the Al‑0.3Zr alloy with impurities content less than 0.01%. Alloying of the Al‑0.3Zr alloy with REMs leads to the formation of (Al, Fe)₃REM phases. The Al₃Fe and Al₈Fe₂Si phases were formed in the Al‑0.3Zr‑0.5Fe‑0.5Si alloy. The Al₁₀Fe₂Er and Al₁₀Fe₂Y phases, as well as the Al₃Er₂Si₂ and Al₂Si₂Y phases, were crystallized instead of the Al₃Fe phase after Er or Y addition. The Al₂Si₂Yb or Al₂Si₂Gd phases with dissolved Fe were present in alloys with Yb or Gd. Iron and silicon impurities lead to a significant boost in hardness increase in all studied compositions during annealing at 400 and 440 °C. Hardening begins as early as 0.5 h into the annealing process and reaches its maximum after 8–11 h. The greatest hardening was achieved after annealing at 400 °C in alloys with erbium and ytterbium. High hardness after annealing of alloy ingots with impurities due to hardening by dispersoids and low silicon content in (Al) makes them promising candidates for creating current conductors characterized by high strength, thermal stability and electrical conductivity.

High-entropy alloys form a new class of metallic materials attracting the interest of researchers by a broad range of attractive properties and applications. The multicomponent FeNiCrCoAlTiCuMoVZrNbW coatings were obtained on 35 steel as a result of electric spark treatment in granules of the corresponding metals. We studied the structure and compositions of the coatings by X‑ray phase diffraction analysis and scanning electron microscopy supplemented by the energy-dispersive analysis. The thermodynamic calculations revealed high-entropy structures of the deposited coatings with BCC and FCC lattices confirmed by the results of phase diffraction analysis. As the duration of discharge pulses of electric spark deposition increases from 20 to 200 μsec, the thickness of the coating increases from 4.7 to 25.8 μm. The water wetting angles of the surfaces of applied high-entropy coatings vary from 102.4 to 106.6°, which means that the surface of 35 steel acquires hydrophobic properties. The heat resistance of the coated samples at a temperature of 700 °C was 3.7–4.9 times higher than for 35 steel. It was discovered that high-entropy coatings may significantly decrease the corrosion potential and corrosion current density of 35 steel in a 3.5% NaCl solution. The microhardness of the coatings varied within the range 5.11–5.31 GPa. As the duration of discharge pulses of spark deposition increases, the friction coefficient of the high-entropy coatings monotonically increases from 0.86 to 0.97. The application of multicomponent FeNiCrCoAITiCuMoVZrNbW high-entropy coatings enables us to attain a 2–4-fold lowering of the degree of wear of 35 steel.

The work is dedicated to the study of the influence of ingot crystallization rates on the structure of formed semi-finished products obtained from Co–Cr–Mo alloy ingots. The study examines the production of ingots by vacuum induction melting with casting into molds made of different materials that provide different crystallization rates for the alloy. The homogenization annealing process and its effect on the structure of ingots with varying crystallization rates were studied. Based on differential thermal analysis, it was demonstrated that the dissolution and precipitation of excess phases in ingots with higher crystallization rates occur at higher temperatures compared to those with lower crystallization rates. The structure of the ingots after homogenization annealing and the forgings obtained from the homogenized ingots were studied using optical and electron microscopy methods. Results showed that in order to obtain deformed semi-finished products with a more uniform structure and a more homogeneous distribution of the σ‑phase, it is desirable to reduce the crystallization rate. The use of ingots obtained with a higher crystallization rate for the production of high quality semi-finished products requires a significant adjustment of the homogenizing annealing and forging regimes.

The study presents the results of industrial trials of the smelting technology of low-carbon ferrochrome from substandard chrome ores of the Sopcheozerskoye deposit. The alloys were smelted in the industrial furnace DSP-bI (6.5 MBA) using several methods: directly from chrome concentrate, as well as by refining the ore-lime melt in order to reduce the iron content. As a result, low-carbon ferrochrome of various grades was obtained, meeting the requirements of GOST 4757-91 (ISO 5448-81). Replacement of ferrosilicochrome with ferrosilicon improved the technological parameters of the smelting process: chromium recovery increased by 9% and power consumption decreased by 11%.

The distribution of natural gas into the blast channel of a blast-furnace air tuyere with a heat-insulating insert enhances the mixing of gas with the blast air and improves combustion efficiency. Numerical simulations were conducted using Ansys to analyze gas dynamics, heat transfer, and natural gas combustion during injection through a collector cavity and a set of holes in the tuyere flange. The effects of the diameter and number of flange holes on tuyere performance were investigated. The thermal and gas-dynamic performance of the tuyere and the thermal stresses in the insert were found to depend on the ratio of cross-sectional areas at the inlet and outlet of the collector.

The paper presents the results of a research study on obtaining an aluminum matrix composite material with an increased degree of reinforcement by decorated multilayer carbon nanotubes. A casting method to increase the mechanical properties of the product, its tensile strength in particular, is proposed. The use of suspension casting allows the tensile strength of low-alloy aluminum alloys to be increased by at least 100%. The work provides an example of strengthening the A6 alloy with the aluminum content of above 99.6%.