Metallurgist最新文献

Low-carbon, low-alloy steels, including coated grades, are among the fastest-growing product segments for metallurgical enterprises. This paper presents examples of the development and implementation of the following types of steels: cold-rolled steels with a minimum yield strength of 420 MPa; deep-drawing interstitial-free (IF) steel; bake-hardenable (BH) steel; and dual-phase steel. Using a systematic approach has been shown to improve product quality and enhance the stability of mechanical properties.

We consider some methods of visual space modeling of the metal flow over the tool–workpiece contact surface and construct the diagram of contact stresses for the process of volume stamping of flat profiled blanks. The results obtained by different methods are characterized by good agreement. The proposed methods make it possible to predict form changes in the blanks and the formation of defects in the macrostructure of the deformed material, as well as to control the process of form changes in the forgings.

In this study, computer simulation was used to plot a pseudo-binary diagram for Fe-9Cr-1Mo steel microalloyed with niobium and containing up to 0.06 wt. % carbon, and the phase-structural mechanisms of its crystallization were clarified. The steel maintains a single-phase structure of high-temperature δ‑ferrite in the entire solidification interval due to one-step crystallization (Liquid → δ) without a peritectic reaction or peritectic transformation. No micron-sized niobium-rich carbide phases were detected by metallographic analysis of the experimental steel ingot microalloyed with Nb up to 0.09 wt. % obtained by remelting in a laboratory vacuum induction furnace. It has been shown that at the crystallization stage, the interdendritic space becomes enriched with Cr, Mo, Si, Mn, Ni, and Nb, which segregate directly and form a solid solution with increased contents of carbide-forming elements. However, insignificant differences in the compositions of the microsegregation zones ensure the maximum possible macroscopic homogenization of the structure, thus allowing for the achievement of various strength classes (e.g., P110, C90, and L80) for the studied steel by properly selecting the final heat treatment conditions.

Metallographic studies of cast and deformed samples revealed thermally stable anomalous “white” zones with an increased content of all alloying elements relative to the standard crystallization zone. At the same time, the internal volumes of the “white” zones, in the form of inclusions with a high-angle boundary, contain a solid solution with molybdenum and niobium contents of up to 2.9–3.1 and up to 0.12 wt. %, respectively. This specifically leads to intensive pitting formation in these zones as early as during the metallographic etching of the samples, thus indicating their low resistance to aggressive environments. Therefore, like any other inhomogeneities in the bulk of a solid solution, the anomalous “white” zones with high-angle matrix boundaries exhibit reduced resistance to aggressive environments. Consequently, an increase in corrosion resistance can be expected by preventing the formation of “white” zones with an increased content of all alloying elements.

This study presents a method for the preparation of pyrite cinders for reductive smelting, a process used to extract an iron-based alloy. The investigation centered on the behavior of copper in the resulting alloy (pig iron) and in the smelting by-product, the slag. The results demonstrate the feasibility of selectively reducing copper without concomitant iron reduction.

Elevation of the heat resistance of the precipitates for wrought heat-treatable alloys of 2xxx series at temperatures higher than 250 °C is one of the most complicated unsolved problems in physical metallurgy of aluminum alloys. The data obtained in recent years demonstrate that, for cast heat-treatable Al-Cu-Mn-Zr-based alloys, the procedure of long-term high-temperature annealing may lead, under certain conditions, to the stabilization of the precipitation structure as a result of significant segregation of the atoms of some alloying elements on the θ′/(Al) interfaces. In the present work, to study this possibility for the case of wrought alloys, we successively perform the operations of homogenization annealing and hot rolling at 450 °C with a total degree of deformation equal to 80%, solid-solution heat treatment at 535 °C/1h with quenching into water followed by aging at 250 °C and stabilizing annealing at 300 °C for 100 h for a new tin-containing alloy with the following composition (wt.%): Al‑4.9Cu‑0.5Mn‑0.14Si‑0.19Zr‑0.1Sn. The level of hardness attained in the alloy as a result of the performed operations was ~87 HV. The analysis of the precipitates carried out by the transmission electron microscopy method demonstrated that, in the process of high-temperature aging at 250 °C/6 h, one can observe the formation of lamellar precipitates with high density of distribution. The subsequent procedure of high-temperature stabilization annealing at 300 °C/100 h leads to a noticeable but nonuniform coarsening of the structure of precipitates. The quantitative analysis performed by the atom-probe tomography (APT) method showed that, as a result of annealing at 300 °C for 100 h, the θ′-phase crystals become saturated with Mn (0.34 ± 0.08 at.%), Si (0.64 ± 0.03 at.%), and Zr (0.04 ± 0.04 at.%). The analysis carried out by the proxigram method revealed high susceptibility of Mn and Zr to segregation on the coherent θ′/(Al) interface; moreover, the most significant role in this case was played by the highest attained concentration of Zr (~0.2 at.%).

This paper examines the influence of refining fluxes (fluorite, boron oxide, and aluminothermic ferroalloy production slag) on the physicochemical properties of the melts. Examples illustrate the use of CaF₂ to improve the refining properties of slag at metallurgical plants, alongside its associated drawbacks. Several studies examining the replacement of CaF₂ with B₂O₃ are reviewed, detailing its impact on viscosity, liquidus temperature, melt structure, thermal conductivity, and the degree of steel desulfurization. One alternative fluidizer for refining slags is Al₂O₃, which positively influences the fluidity and desulfurization capacity of CaO–SiO₂-based slags. Experimental heats were conducted using a solid slag mixture containing 58% Al₂O₃, 26% CaO, and 0.4% FeO at the ArcelorMittal Temirtau plant. The optimal consumption rate for this mixture was determined to be 0.7–1 kg per ton of steel.

The paper presents the results of a thermodynamic analysis of the distribution of sulfur and copper during the interaction of elemental sulfur with copper smelting slags based on the developed mathematical model and algorithm for its implementation. The model is based on the assumption that at each moment of time when elemental sulfur is fed to the melt, a thermodynamic equilibrium is established between the slag and the gas phase, as well as between the slag, matte (when it appears in the system), and the gas phase. The model consists of two consecutive calculation blocks. The first block describes the distribution of components at the stage of slag sulfidation without the formation of a sulfide phase. The second block describes the distribution of components during slag sulfidation with the formation of a sulfide phase. The satisfactory agreement was shown between the calculated and experimental data obtained during sulfidation of commercial copper smelting slags in the laboratory at a temperature of 1300 °C and elementary sulfur consumption of 3–21% of the mass of the initial slag. Model-based calculations confirmed the high percentage of sulfur released into the gas phase (more than 40%) obtained in laboratory experiments during sulfidation of slag with elemental sulfur without the use of a reducing agent. To analyze the effect of the redox potential on the parameters of slag sulfidation with elemental sulfur, calculations were carried out at different fixed values of CO/CO₂ ratio in the gas phase ranging from 0.15 to 2. It was shown that at increased CO/CO₂ ratios (~ 0.5–0.6), the release of sulfur into the gas phase sharply decreases, while the matte yield increases. The absorption of sulfur by the melt exceeds 98%. The obtained results can be used to select process conditions of depleting copper smelting slags by sulfidation with elemental sulfur.

Air bending is widely used in the low-volume or custom manufacturing of thin-walled enclosures for small devices. This process involves maintaining an air gap between the sheet metal and the walls of a V-shaped die. In the process of V‑bending, the technological tooling can leave marks on the surface of the deformed part, such as dents, scratches, and other defects. In order to avoid damage to the surface of the metal sheet by the technological tooling during V‑bending, the maximum contact stresses (σ_con) generated by the punch acting on the sheet material should not exceed the permissible crushing stress (σ_cr). In this study, the permissible crushing stress (σ_cr) was calculated using a formula based on the material’s yield strength and ultimate strength during deformation. To determine the maximum contact stresses (σ_con) during the elastic contact between a cylinder and a plane, which is characteristic of the initial stage of air bending, the Hertz-Belyaev approach was used, while the deformation force was calculated using a standard formula from the sheet metal forming theory. An expression was derived to determine the permissible punch radius, i.e., the minimum radius required to prevent the surface of the deformed metal from crushing. As a result of performed calculations, the relationships between the permissible punch radius (R_p), thickness of the sheet material, and distance between the working edges (groove width) of the die were obtained. The proposed methodology was successfully applied to develop technologies for step bending of thin sheet metal made of low-carbon and corrosion-resistant steels.

This study investigates the microstructure, texture, and properties of high-strength K70 and K80 steel pipes that were subjected to full-scale pneumatic testing. The testing was done to evaluate the suitability of the pipes for next-generation gas trunk pipelines that operate at a pressure of 14.7 MPa (150 atm). The results are compared with previously accumulated data on K65 grade pipes, which were developed for and used in the construction of the Bovanenkovo–Ukhta gas pipeline, which was designed to operate at an elevated pressure of 11.8 MPa (120 atm). A characteristic feature of fracture in pipe base metal with insufficient crack resistance includes a limited plastic deformation zone, a relatively low degree of deformation at the fracture point, and numerous splittings along the rolling plane on the fracture surface. This fracture mode involves uncontrolled crack propagation along the pipe string under high test pressure and is linked to these microstructural characteristics. Despite its high impact toughness values, the K80 grade pipe steel, which has higher strength but significantly lower ductility than the K70 grade, does not effectively arrest running cracks. This study investigated how structural banding and texture characteristics influence the propensity for splitting formation upon fracture in a series of experimental pipes from both strength classes. The results suggest that increasing the intensity of the rotated-cube texture component decreases the toughness measured by instrumented drop-weight tests. Additionally, deformation zone characteristics from full-scale field tests with those from drop-weight tear test specimens for the examined strength grades were compared. Analysis revealed that K80 pipe metal exhibits the least plastic deformation and consequently the lowest fracture energy. In contrast, the K65 and K70 grades demonstrate significantly higher values for these characteristics, confirming their suitability for high-pressure gas pipeline construction.

The paper examines the specifics of the cold straightening process for K60 plate produced on a 5000 mill. The stress–strain state of the strip during cold straightening is evaluated, and the effect of cold straightening on the mechanical properties of the finished plates is analyzed. The relationship between plate ductility and straightening temperature and intensity is established.