Metallurgist最新文献

In this study, using an example of cold-rolled sheets, the separate effect of magnesium and zinc in an amount up to 2% upon the structure and mechanical properties of a thermally non-hardening heat-resistant alloy Al–2%Cu–1.5%Mn, the composition of which is optimized to obtain the maximum fraction of Al₂₀Cu₂Mn₃ phase, is studied. It is found that in a cast state, zinc is completely contained within aluminum solid solution, and magnesium is partially included within eutectic particles of the Al₂CuMg phase. These elements hardly affect the amount of Al₂₀Cu₂Mn₃ phase, which is formed during deformation and heat treatment in the form of nanoscale dispersoids. It is found that addition of 1% magnesium increases the strength of cold-rolled sheets of the base alloy by 15% after 3‑hour annealing at 400 °C, without reducing the ductility. In turn, alloying with zinc does not have a significant effect on strength.

Based on a literature review, the relevance and necessity of processing e‑waste are shown. Pyro-, hydro- and biometallurgical methods for processing e‑waste are briefly described, and the advantages and disadvantages of existing technologies are compared. The efficiency and the environmental and health impacts of various technologies are analyzed.

The low-temperature chlorination technology applied to e‑waste processing is given a thermodynamic interpretation to obtain additional information necessary for better understanding of the behavior of gold and other non-ferrous metals with low metal content. The mechanism of the interaction between e‑waste elements and gaseous chlorine during low-temperature roasting was studied. The behavior of metals at low temperatures of chlorination of e‑waste (below 673 K) was assessed from the changes in the thermodynamic quantities of the system. Thermodynamic calculations were conducted to determine the Gibbs free energy ((Updelta {G}_{T}^{0})) of the reactions between e‑waste elements and gaseous chlorine at various temperatures. Based on the thermodynamic calculations of the reactions of precious (gold, silver, platinum, palladium) and other non-ferrous metals (Cu, Pb, Zn) with gaseous chlorine at low chlorination temperatures of 323–673 K, it was established that it is possible to selectively recover gold as sublimates Au₂Cl_6(g) and to produce a solid-phase cinder containing solid chlorides of precious and non-ferrous metals. The low-temperature chlorination roasting of e‑waste is a good prerequisite for the integrated recovery of gold and other precious and non-ferrous metals with high efficiency. The obtained results will be used for the selection, justification, and science-based design of innovative technology for processing e‑waste, using not only gaseous chlorine, but also solid chlorine-containing reagents (CaCl₂, NaCl).

It is shown that laser melting of a steel surface within a permanent magnetic field enhances the Marangoni effect, i.e., it intensifies metal mixing up to removing part of a thin liquid metal layer from an irradiated surface. It is established that during laser thermomagnetic treatment under the action of Lorentz forces the depth of hardened layer increases by 15–25%. It is established by calculation that during laser processing within a permanent magnetic field under action of the Righi-Leduc effect, temperature gradients, the level of thermal stresses and degree of metal local plastic deformation within the irradiated zones decrease. This leads to a reduction in steel surface layer hardness by 15–20% compared with laser hardening without applying a magnetic field. It is shown that during laser thermomagnetic treatment, under magnetostrictive effects action, partial decomposition of laser-hardened martensite proceeds with dispersed carbide hardening action. As a result of occurrence of independent low-temperature tempering within steel there is a reduction in structural stresses and the danger of crack formation.

This paper presents new technology for stainless steel wire processing. This technology consists of using cryogenic cooling immediately after the wire leaves the drawing die. Results of a laboratory experiment show that use of cryogenic processing after wire drawing improves mechanical properties compared with traditional drawing. Metallographic analysis proves that deformation conditions during cryogenic drawing are an additional factor for realization of structural resources to optimize steel wire physical and mechanical properties.

This paper presents experimental results of a study of the occurrence of electricity emission in the process of chemical-and-thermal treatment (CTT) and their theoretical justification. Oxide materials with semiconductor properties, along with metals, can form electric fields in technological mixtures that are used in processes related to the transfer of saturating elements to the hardened surface of a part made of steel X35CrNi2-3. The contribution of these fields to the transfer of saturating elements is comparable with that of a concentration field. A design and manufacturing technique for a measuring cell is proposed to determine the magnitude of the emission current arising in the process mixture. An equation is obtained that describes the general process of solid-phase saturation of parts with the participation of concentration and electric fields during CTT.

The electrochemical synthesis of sodium ferrate for water purification is a promising solution to the problem of clean water. The materials and methods required for the process are considered. Particular attention is paid to the material and technology of obtaining an electrolytic cell that ensures stable and safe production of sodium ferrate. Different recirculation rates and their influence on the final product are considered.

Results of an experimental study of temperature distribution along the length of a solid mandrel made of 4Kh5MFS steel in a screw mill 30–80 of Bogorodsky Branch of JSC NPO Pribor during hot rolling of vessels made of steel grade 50 are presented. It is revealed with computer modelling that there is uneven distribution of temperature up to 250 °C along the length of a mandrel from 350 to 600 °C, which leads to crack formation at its surface with a size of about 1.6 mm and a decarburization layer of about 0.8 mm. Regularity of the influence of temperature unevenness along the length of a mandrel on unevenness of hardness distribution from 22 to 50 HRC is established. Results of the study make it possible to develop a mandrel design with the possibility of internal water cooling during broaching vessels in a 30–80 mill. It is shown that use of a water-cooled mandrel made of C0.4Cr5MoVSi steel makes it possible to preserve the original grain structure with a grain size of about 9 points, reduce the decarburization layer by a factor of four, while formation of external defects in the form of cracks is not detected. Based upon calculations of the efficiency carried out at the Bogorodskii Branch of JSC NPO Pribor, it is found that use of a water-cooled mandrel within mill 30–80 will increase its durability by 10% and reduce deviations from permissible geometric dimensions of the cavity of vessels made of steel 50 by 8%.

Mechanical synthesis of the powders based on the Al-6Mg nanocrystalline matrix, multi-reinforced with fullerenes (C₆₀) and ceramic particles (AlN), was performed. The effect of the AlN content in the charge, ranging from 10 to 50 wt. %, on the morphology of particles, and the granulometric composition of the synthesized multi-reinforced powders were studied. The structural and phase composition of the synthesized powders was analyzed. The microhardness of the multi-reinforced composite powder particles was measured using kinetic indentation. It was shown that by increasing the concentration of ceramic filler (AlN) from 10 to 50 wt. %, it becomes possible to increase the microhardness of the powder particles by about 12–20% compared with the mono-reinforced composite particles.

The paper presents the results of studying the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the physical and mechanical properties of aluminum alloys AK9 and AK12 obtained by using a stir casting and suspension casting technologies. When conducting experiments on stir casting MWCNTs, limitations were revealed, such as the difficulty of their uniform distribution in the melt, as well as a decrease in efficiency when increasing the thickness of the cast piece and/or performing sand-mold casting. A comparative analysis of the samples was carried out, which showed that the use of multi-walled carbon nanotubes (0.1 wt. %) as micro-additives leads to an increase in the tensile strength of the composite by at least 15% provided their uniform distribution. However, at increased casting thickness, samples obtained by using a suspension casting technology demonstrate higher mechanical properties. In addition, the suspension casting technology enables an increased productivity without equipping the furnace with a stirring device.

Low-carbon Cr-Ni-Mo steels widely used in mechanical engineering are studied: 18Kh2N4MA, 25Kh2N4MA, 25KhN3MA. Thermokinetic diagrams are plotted by a dilatometric method. Temperature-time ranges for microstructure constituent formation are established. It is shown that bainite within the steels studied may be formed both above and below the M_s temperature. Features of isothermal bainite transformation are investigated, kinetics of bainite transformation are determined, as well as the quantitative ratio of microstructure constituents formed as a result of austempering. It is established that the largest amount of bainite within the steel structures studied (80–95%) is achieved at a temperature near M_s. Mechanical properties (strength, ductility, impact strength) of the steels being studied are analyzed after various heat treatment methods: various cooling intensities, upper and lower bainite austempering. It is shown that formation of upper bainite has an ambiguous effect on steel impact strength.