Metallurgist最新文献

A chromium-boron mixture with the atomic composition corresponding to CrB₂ was subjected to mechanical activation in a high-energy planetary mill for 6–40 min at a balls-to-material ratio of 20:1. The milled powders were analyzed by X‑ray diffraction and other methods. Then the mixture was heated at an initial rate of ~ 6 °C/s to a temperature of 1000 °C. Exothermic peaks associated with the formation of borides were observed on the heating curves. The onset temperature of this transformation decreased with the milling time to 15 min and then reached a plateau. This is due to the formation of a thin layered structure as the milling time increases and the limit of structure thinning is reached. The optimal milling time for preparing the mixture for self-propagating high-temperature synthesis should be 15–20 min, since the thinning of the roll layers after this practically stops or becomes very slow. At such milling duration, boride formation does not occur in the grinder, that is, the energy charge of the mixture is not consumed. At the same time, some literature data suggest that during milling for 40 h, up to 50% of boron is converted into CrB₂.

One important tellurium source may be the ores of the Baleysky ore field in Transbaikalia. Our studies of the material composition of the gold-silver ores in the Baleysky ore field enabled the first analysis of the tellurium and selenium content in the primary and oxidized ores of the Baleysky ore field. Moreover, it has been established that tellurium in run-of-mine ores is within the limits of its association with certain mineral forms of gold and silver. The article considers their parageneses. The average tellurium content is 0.65 g/t. The average selenium content amounts to 2.59 g/t. However, no principal selenium minerals were found in the ores of the Baleysky ore field. Additionally, we developed a framework for the hydrometallurgical method of extracting tellurium and selenium from the tailings left over after processing gold-silver ores of the Taseyevsky deposit (its undeveloped reserves amount to about 105 t) and the Baleysky ore field (its gold resources by category P1 are approximately 35 t).

The possibility of producing multilayer billets by wire arc additive manufacturing (WAAM) technology with layer-by-layer forging using Cr20Mn5Ni4Mo2.5Cu3N0.3 flux-cored wire of 1.6 mm diameter as electrode material is investigated. The applied method resulted in the production of a weld metal with austenitic-ferritic structure (δF ≈ 1.5 vol %) without defects, which demonstrates a good combination of strength and plastic properties (σ_B = 960 MPa, σ_0.2 = 670 MPa, δ = 35%).

This article examines the influence of iron stearate and sintering conditions on the structure and properties of powder alloy steel SP50S2KhF. Studies have been carried out to establish the influence of temperature and soaking time during sintering on the structure of powder steel SP50S2KhF. At a sintering temperature of 1200 °C and soaking time of 120 min, practically no undissolved ferroalloy particles are observed in the structure, and the pores have a round shape. The structure of the samples after sintering consists of alloyed ferrite and pearlite. As a result of studying the mechanical properties, it was found that the addition of iron stearate to steel SP50S2KhF has a positive effect on its mechanical characteristics. At higher iron stearate content, an increase in hardness and bending strength is observed.

In the process of manufacturing iron-aluminum alloys, the prospects of reducing the costs spent for the refractory and charge materials, as well as for the supply of thermal and electric energy are connected with the realization of the exothermal process of melting of the thermite charge, i.e., in fact, industrial wastes in the form of scale and metal shavings, in the reactor without applying traditional melting units. In view of the high temperature of formed melts, it seems reasonable to use carbon materials as refractories. The durability of the reactor strongly depends on the number of thermal cycles and the possibility of ensuring the mechanical strength and functionality of its elements subjected to the most aggressive thermal effects of the melts. As a result of a series of experiments, we determine the possibility of weakening of the thermal effect of iron–aluminum melts formed as a result of the exothermal reaction on the material of the graphite reactor by regulating the content of active aluminum. Moreover, we propose a version of measures connected with the possibility of updating the design of the graphite reactor aimed at increasing its service life.

Fine dust from copper smelting production is processed together with zinc cake in Waelz kilns of a zinc plant to recover non-ferrous and precious metals. The resulting clinker into which copper, precious metals, and most of arsenic pass is used in the smelting of copper-containing raw materials, which causes undesirable accumulation of arsenic in inter-plant circulation. Moreover, the presence of chlorine and fluorine in dust necessitates their removal in the zinc recovery process. It appears rational to use dearsenizing roasting to remove arsenic, chlorine, and fluorine from dust before zinc production. The chemical and phase compositions of dusts are presented. Laboratory studies and pilot tests were performed to determine the optimal roasting conditions. The mode of mixing the starting dust was determined: 90–95% dust, 5–7.5% petcoke, 0–5% calcium oxide, 0–2% pyrite. It was proposed to roast a granulated charge in a rotary tubular kiln at a temperature of 1050 °C for two hours. With these parameters, the degrees of sublimation of arsenic, chlorine, and fluorine were 78–85%, > 95%, and > 97%, respectively, the loss of zinc with sublimates being 4.3–7.2%. The resulting clinker (yield = 51.9–67.4%) can be used to recover zinc at a zinc plant, while sublimates (3.3–4.9% Zn, 23.9–28.0% Pb, 25.4–38.6% As, < 2.6% Cl, < 0.04% F) are additionally processed to separately recover lead cake and transform arsenic to stable form for subsequent utilization.

We performed computer simulations of the screw piercing of titanium-nickelide shells in two- and four-high mills. On the basis of the accumulated numerical results, we compute the parameters of the stress-strain and thermal states of the shells. The distributions of levels of the accumulated strain and the normalized mean stress show that a more homogeneous stress-strain state and a lower hazard of fracture of the shells are detected in the case of four-high piercing. The analysis of the temperature distribution shows that, in the case of four-high piercing, the obtained temperature state is more favorable for guaranteeing higher levels of plasticity of the materials of pierced shells.

This work investigates the influence of small additions of aluminum on the structure of ingots from a high-entropy alloy of the (Fe_0.25Co_0.25Ni_0.25Cr_0.125V_0.125)₈₃B₁₇ composition. The structure of experimental alloys was analyzed using scanning electron microscopy and EDX analysis. The borides formed in the structure were analyzed by transmission electron microscopy, X‑ray diffraction, and electron backscatter diffraction. Aluminum addition was found to change the crystallization process of the alloys, affecting the type of primary boride crystals and eutectic composition. The addition of aluminum to the alloy in greater amounts changes the boride type from refractory boride of (V, Cr)B type to a more easily melting type of boride M₃B₂.

The results of studying the structure and properties of master-alloy rods produced from AD31 alloy extrusion waste by direct extrolling are presented. A SLiPP‑2.5 unit, which is part of the combined processing line in the laboratory of the Department of Metal Forming of the School of Non-Ferrous Metals of the Siberian Federal University, was used to make rods with a diameter of 9 mm from AD31 alloy waste. The process parameters for producing rods from AD31 aluminum alloy by direct extrolling were determined: elongation = 16.5, melt temperature = 760 ±10 °C, rolling strain = 50%, roll speed = 5 rpm. It was established that the initial structure of the master-alloy rod affects the melt, and the rods made from AD31 alloy extrusion waste by direct extrolling have a stable ultra-fine subgrain structure, which allows them to be applied to AD31 alloy. The Alcan test revealed that introducing 3 to 4% rod with a diameter of 9 mm into a solidifying AD31 alloy ingot at a melt temperature of 720 °C and a melt holding time of at least 3 min ensures a stable modifying effect.

In this work, we investigate specimens of rolled structural pipe steels of industrial smelting at NLMK PJSC and those of laboratory smelting with various alloying systems (C–Mn–Si, C–Mn–Si–Cr, C–Mn–Si–Cr–Cu, and C–Mn–Si–Cr–Ni–Cu) subjected to dynamic corrosion tests in circulating calcium-chloride environments with different contents of aggressive ions, typical of the Khanty-Mansiysk region. The laboratory-smelted specimens with a chromium content of 0.6% in the absence of corrosive nonmetallic inclusions in the metal exhibited the lowest corrosion rate. The corrosion film was established to consist of three layers, different in appearance, structure, and chemical composition. Only one of the layers, referred to as “gray” by its color, is characterized by increased Cr and Cu contents, thereby being promising for application in the studied corrosive conditions. A mutual positive effect of Cr and Cu additives on the corrosion resistance of structural steels, exposed to the aggressive environments typical of the Khanty-Mansiysk region, is established.