Metallurgist最新文献

This study is devoted to the production of ceramic matrix composite materials based on borides with a binder made of a high-entropy alloy CoCrCuFeNi using powder metallurgy methods. The composite materials were synthesized by hot pressing of powder mixtures after high-energy ball milling in planetary centrifugal mills. The ceramic matrix of the composites was based on borides (Cr₄B, Cr₂B, CrB, and Ni₃B), while the metallic binder consisted of a solid solution of all metallic components, with a face-centered cubic crystal lattice. The resulting boride-based cermets are characterized by a combination of high hardness, strength, and ductility. With a boron content of up to 20 wt. %, the cermets were comparable in strength to the high-entropy alloy CoCrCuFeNi (1600 MPa) with a hardness of up to 8.34 GPa. The wear resistance of the developed cermets correlates with the boron content and the proportion of boride phases. Samples with a boron content of 40–50 wt. % demonstrate extremely high wear resistance, with a friction coefficient of approximately 0.5 when paired with Al₂O₃.

This study investigated the microstructure and phase composition of VT22 alloy produced by pendant drop melt extraction, following heat treatment (HT) in the temperature range of 500–900 °C. The applied HT parameters were selected to simulate the sintering conditions anticipated during the fabrication of sintered fiber materials-specifically, reinforcing frameworks for advanced aluminum-matrix composites. Following rapid solidification, the alloy exhibits a fine-grained microstructure and a metastable phase composition. The results indicate that increasing the treatment temperature induces the decomposition of metastable phases (β and α″-martensite), ultimately leading to the formation of a stable α+β two-phase structure. The heat treatment temperature significantly influences the morphology of the precipitated α‑phase particles, which range from nanoscale (up to 150 nm) to microcrystalline dimensions (approximately 2 μm). Notably, no substantial grain growth is observed, with grain size remaining below 40 μm even after heat treatment. The evolution of phase composition and microstructure strongly affects the microhardness of the rapidly quenched alloy. Maximum hardness (559.2 ± 6 HV) is achieved after low-temperature treatment, which results in the precipitation of nanoscale α‑phase particles. After HT in the range of 800–900 °C, both phase composition and properties stabilize, with average microhardness values varying between 430 and 450 HV. These findings underscore the necessity of selecting optimal fiber sintering conditions based on the mechanical property requirements of the sintered fiber materials.

In metallurgical processes, especially in pyrometallurgy (production of copper, zinc, lead, and other metals from sulfide ores), large amounts of sulfur dioxide are released in the processes of roasting and smelting. The problem of neutralization of sulfur dioxide released in the course of processing of sulfide ores and in some other metallurgical processes is an important ecological and commercial task. As a result of efficient removal of SO₂ from metallurgical exhaust gases not only decreases harmful emissions, but also allows one to obtain various valuable products, such as free sulfur and sulfur-containing compounds. For the implementation of processes of this kind, it is necessary to have new (more efficient) catalysts obtained on the basis of available local raw materials.

In the present work, we synthesize various nickel-containing catalysts by the impregnation method based on local clinoptilolite samples and study their catalytic activity in the process of hydrogen reduction of sulfur dioxide to elemental sulfur. The experimental conditions were as follows: the rate of volume flow of the gas mixture W = 500–1500 h⁻¹, the H₂:SO₂ ratio = 2.0–2.2, the catalyst particle size = 0.5–3 mm, and the volume fraction of SiO₂ in the gas mixture = 10–30%.

It is established that nickel-containing catalysts based on clinoptilolite exhibit high catalytic activity under the conditions typical of metallurgical exhaust gases. The optimal parameters of the process of hydrogen reduction of SO₂ sulfur in the presence of catalysts with a nickel content of 10 wt.% are as follows: W = 1000 h⁻¹, H₂:SO₂ = 2.1, and T = 773 °K. Based on the accumulated experimental data, we perform mathematical modeling, which makes it possible to predict the behavior of the system in various modes and under different conditions.

We study the influence of the characteristics of structural state on the mechanical characteristics of low-carbon hot-rolled Mo-containing steels of three microalloying systems (Ti-Mo, V‑Mo, and Nb-V-Mo) depending on the temperatures of termination of rolling and coiling of the strip. It is shown that the highest levels of the characteristics of strength and ductility are exhibited by steels with a single-phase ferritic microstructure microalloyed with titanium and molybdenum. In this case, the metal matrix consists of ferrite of two morphological types: polygonal and block. High levels of strength are attained as a result of precipitation hardening caused by a large number of nanoscale interphase precipitates. This process is facilitated by relatively high temperatures of termination of rolling (860–880 °C) and coiling (570–590 °C) and molybdenum concentrations not lower than 0.16 wt.%.

This review summarizes the specifics of aluminum alloying with small additions of zirconium and scandium, since the middle of 20th century. The experience accumulated in the field of alloying technologies, as well as thermal and thermomechanical treatments made it possible to develop novel, heat-resistant (up to 300–400 °C) high-performance Al–Sc–REM conductors and sparingly alloyed Al–Zr–REM–Fe–Si conductors. Alloy compositions and the conditions of thermal and thermomechanical treatment were developed based on in-depth research studies of the dispersoid formation processes in the considered compositions during annealing, deformation, and post-deformation annealing. Thermomechanical treatment, including ingot annealing for maximum hardness, hot and cold rolling, and post-deformation annealing at 300 and/or 360 °C, provides the new conductors with an excellent combination of strength properties and electrical conductivity.

Computer modeling of three-roll screw rolling processes for steel billets was performed using the QForm finite element analysis environment at roll feed angles of 12° and 20°. The QForm point tracing function was employed to construct the helical surfaces described by points on the billet diameter during rolling. The coordinate data of the traced points defining these helical surfaces were divided into four groups based on the dimensions of the actual deformation zone. A statistical and geometric assessment of the helicity of the resulting helical surfaces was conducted for each group. It was established that helicity can occur only when the traced points are located on the entry side, outside the boundaries of the actual deformation zone.

The paper presents the initial characteristics of the metal-powder compositions (MPC) of alloy VZhL718 (IN718) used in this study, obtained by the plasma rotating electrode process (PREP) and vacuum induction gas atomization (VIGA), including chemical composition, processing properties, MPC particle size distribution parameters, and morphology.

The contents of gaseous impurities were determined for the MPCs in the initial state and after a single selective laser melting (SLM) cycle, as well as for the SLM-synthesized samples. Explanations of the resulting differences were provided.

The porosity of the VZhL718-PS samples (PS = powder-based, synthesized) synthesized from PREP-derived powders was evaluated and compared with the existing porosity data for the VZhL718-PS material synthesized from VIGA-derived powders. Assumptions were made regarding the impact of the MPC production method on the observed differences.

The surface roughness of the VZhL718-PS samples synthesized from PREP- and VIGA-derived MPCs was measured. Differences in roughness levels of the samples were determined, and roughness variation patterns were established for the upper and lower sides of the samples at different inclination angles. Explanations for the observed differences were provided.

Mechanical properties were determined for the VZhL718-PS samples synthesized from PREP-derived MPC in the XY direction after complete heat treatment. The obtained results were compared with the available data for the VZhL718-PS material synthesized from VIGA-derived MPC.

We present the investigation of transformations of the surface cracks in continuously cast slabs in the course of thick-plate rolling of the metal. A finite-element mathematical model adapted to the conditions of thick-plate rolling is used to describe the stress-strain state of the metal in the presence of surface cracks in the slab. It is shown that axial and edge longitudinal cracks extend in the direction of rolling with a substantial decrease in the width and depth of the defects. The axial and edge transverse cracks open in the process of rolling and transform into defects in the form of deep films exhibiting a trend to subsequent growth. An edge crack opens in the course of rolling and transforms into a surface defect in the form of a skin with a trend to grow during plastic deformation. A transverse crack on the lateral face opens in the process of rolling and transforms into a longitudinal defect without changes in the depth. A longitudinal crack on the lateral face closes in the first deformation passes under the action of compressive stresses and can be completely removed by trimming the side edges.

A technological process and design concept for a profiling mill to roll round tubes into hexagonal tubes made of boron-alloyed steels have been developed. Key relationships for calculating the rolling parameters are presented, and prototype tube samples have been rolled. Profiling (drawing) of round tubes into hexagonal form is shown to achieve high geometric accuracy and good surface quality.

Promising high-chromium steels, such as 13Cr-2Ni-Nb‑V, 13Cr-3Ni-Mo-Nb-Ti, 13Cr-3Ni-Mo-Nb, and 13Cr-4Ni-Mo-Nb-Ti, were developed and fabricated under laboratory conditions for the production of seamless hot-rolled threaded pipes. As a result of heat treatment of these laboratory steels, including double quenching and high-temperature tempering, the achieved mechanical properties of the pipes were consistent with strength classes C90 and P110 in a cold-resistant state. This was attributed to the formation of a fine-dispersed tempered sorbite structure. For the studied steels, mathematical modeling using the TC-Prisma module of the Thermo-Calc software package helped determine the onset temperatures for the formation of high-temperature δ‑ferrite known to adversely affect the cold resistance of high-chromium steels. The studied steels are characterized by high corrosion resistance in a carbon dioxide (CO₂) environment, while 13Cr-3Ni-Mo-Nb and 13Cr-4Ni-Mo-Nb-Ti steels also demonstrated enhanced resistance in a hydrogen sulfide environment when tested for sulfide stress cracking (SSC).