Metallurgist最新文献

The article presents the results of studies into the physical and mechanical properties of a material obtained by metallurgical smelting according to a technological scheme for creating alloys based on mineral raw materials of Yakutia. It was found that, in terms of its physical and mechanical properties, the alloy belongs to the class of cast tool steels according to GOST 1435-99. The fine-grained homogeneous structure of the alloy indicates its improved physical and mechanical properties. The ultimate tensile strength and hardness of the material correspond to the values of high-quality carbon steels after normalization. The feasibility of using iron ores of sedimentary origin from the Mene-Aldan ore occurrence in the development of tool cast steels and alloys has been confirmed.

The depletion of natural reserves and the accumulation of large-tonnage waste containing significant quantities of non-ferrous and precious metals make the processing of man-made raw materials increasingly critical. Unlike ores and concentrates whose mineral structure is often well understood, data on the phase properties of metallurgical waste are quite scarce. This information can serve as a starting point for selecting a rational and effective technology for recovering precious elements from such waste. The processing of zinc clinker, which is one of the most large-tonnage non-ferrous wastes, is discussed using the Elektrotsink dumps as an example. Modern methods are used to study the material and phase compositions of an increment clinker sample and the speciation of precious elements such as copper, zinc, gold, and silver. The main phases (up to 40%) are simple and complex iron oxides and silicates and quartz SiO₂ (up to 15%). The total fraction of copper, zinc, and iron sulfides does not exceed 15%. The content of these elements does not exceed several percent. Particular attention is paid to the phases that determine the quantitative indicators of the concentration and hydrometallurgical processes in clinker processing: carbon (coke) and ferrites. The composition of clinker is highly heterogeneous, with intergrowths of different phases of variable composition. The content of precious elements in different clinker samples can vary widely.

We discuss the possibility of pressure treatment of workpieces with the help of screw rolling aimed at subsequent production of the working parts of continuous mandrels of the mill. We performed the experimental rolling of ingots obtained by the method of electroslag remelting. In the present work, we also propose qualitative assessments of the micro- and macrostructures, which confirm the possibility of application of the procedure of rolling of workpieces in the course of subsequent production of the working parts of mandrels of continuous mills.

In this paper, we analyze effects of hot rolling on the shape, structure, texture, and properties of a Ti–4.5Al–3Mo–V alloy (VT14) titanium alloy. The phase composition, texture, and morphology of the formed phases in the initial state and after rolling are determined. The effect of the deformation degree between the passes on the formation of various components of the deformation texture and recrystallization is shown. The dependence of VT14 alloy widening during flattening under the action of hot deformation in one pass are analyzed. A decrease in the widening coefficient at a similar degree of deformation is noted. Relationships between the studied hot deformation routes, the α/β-phase ratio, the morphology of the secondary α phase, the development of recrystallization in the β phase, as well as the hardness and contact elasticity modulus of VT14 alloy were determined.

In the present work, we study the possibility of application of a special calibration of the working rolls containing calibration sections of limited length, in the process of radial shear rolling of alloys of the Co-Cr-Mo system and its influence on the parameters of the process and formation of the microstructure. The results of computer simulations demonstrate that the proposed calibration enables one to decrease the radial force applied to the roll by 12–25% and the drop of temperature in the deformation zone between the center and the surface by 5–7%. At the same time, we observe a decrease in the process cyclicity by 20% and the level of maximum compressive stresses increases by 10–15% as compared with the rolls of traditional configuration. The experimental testing of the proposed calibration revealed the stable process of rolling, and the bar obtained as a result did not have any external and internal defects. The analysis of microstructure revealed certain difference between the mean grain sizes at the front and rear ends of the bar, as well as in the central and subsurface areas caused by the different temperature and deformation conditions of rolling. The accumulated experimental data confirm the possibility of radial-shear rolling of high-strength alloys of the Co-Cr-Mo system with elongation ratio up to two even for a significant lowering of the surface temperature of the bar.

The article is dedicated to the study of heat treatment processes of sintered powder steels, with a focus on austenitization processes. The authors consider the specifics of structural transformations occurring during heating and austenitization of sintered powder steels. The study presents an analysis of the influence of chemical composition, porosity, and structural defects on the kinetics and mechanism of austenitization processes in sintered powder steels with ultrafine particles. It is shown that porosity has a significant effect on the heating rate, the dissolution of carbides, and the processes of austenite homogenization. The obtained data contribute to the understanding of the specifics of structural transformations during the heat treatment of sintered powder steels and can be used to optimize process conditions.

The susceptibility of experimental alloys to cracking during fusion welding was evaluated by fishbone testing and the method developed at the Bauman Moscow State Technical University (BMSTU). In terms of weldability, the experimental Al–2Ca–2.5 Mg–0.4Mn (alloy 2B) and Al–1Ca–5.5 Mg–0.5Mn (alloy 1B) alloys are comparable to commercial AMg3 and 1915 aluminum alloys, respectively. Alloying of zirconium alloy (alloy 1) led to a decrease in resistance to cracking during welding. Additional alloying of alloy 2B with scandium had a beneficial effect on its susceptibility to crack formation at an arc current of 90 A. For alloy 4, an increase in the arc current of up to 95A was accompanied by a significant increase in the crack susceptibility coefficient of up to 75%, which indicates the need to use filler wire to obtain joints from this alloy during argon arc welding. Joint alloying of the studied alloys with zirconium and scandium contributes to the destruction of axial crystallite in the weld metal (when welding without filler wire) and the overall increase in the resistance of the weld metal to crack formation during welding.

Using results of testing industrial batches of 23 mm thick steel heavy plates after thermomechanical rolling and subsequent post-welding heat treatment, features are analyzed for fatigue crack formation within a specimen fracture during CTOD (Crack Tip Opening Displacement) testing for fracture toughness. Visual, microstructural, and fractographic studies are conducted on the nature of fracture formation and fatigue crack propagation mechanisms. Probable causes of a potential “pop-in” effect on load-displacement diagrams of notch opening displacement are described, as well as its potentially unfavourable effect on test result interpretation.

The problem of thermal stresses is considered. The process of electric arc welding of E40 steel at low temperatures is simulated. It is demonstrated that it is possible to use a flux-cored wire with an aluminothermic filler to reduce the residual stresses. The heat source is modeled by a double ellipsoid proposed by John A. Goldack. It is assumed that the plate material is elastoplastic and that strains are small and have elastic and plastic components. Reversible (elastic) strains are related to stresses by the Duhamel–Neumann law, while irreversible (plastic) strains arise and develop due to plastic flow according to the associated plastic flow law. It is established that the combined thermal effect increases the temperature range in which welding of E40 steel is possible, which is confirmed by the intensity of residual stresses.

The results of metallophysical studies of the specific features of steel and alloy structure after a thermal-deformation exposure to laser radiation are presented. It is shown that the locality of laser treatment in combination with high heating and cooling rates, lack of soaking at the heating temperature, and high temperature gradients along the depth of the irradiated layer lead to the appearance of thermostrictive stresses of up to ~ 320 MPa in value, which play an important role in strengthening the surface of steels and alloys. It has been discovered and confirmed that under the influence of stresses, a localized plastic deformation develops in the microvolumes of the irradiated material, accompanied by the movement of dislocations along the slip planes. Schemes are proposed for the formation of slip lines or bands, kink bands, relief grain boundaries, etc. during high-speed laser treatment. It has been shown that as a result of laser treatment, the defect density of the crystalline structure of the studied single-phase steels and alloys increases to (2–4)×10¹¹ cm^-2. This contributes to the improvement of mechanical properties (including hardness and shear stress) of the surface layers of irradiated materials. As a result of metallophysical studies, structural relaxation effects of thermostrictive stresses in the laser-treated zones of steels and alloys have been confirmed. By using practically single-phase (“model”) alloys, such as copper and nickel alloys, corrosion resistant steels, and technical iron, it was shown that partial stress relaxation occurs due to dynamic polygonization and recrystallization processes that occur within the surface layers of the alloys, resulting in the formation of small fragmented grains measuring 0.5–2.0 μm in size. This reduces the risk of crack formation due to extreme thermal effects of laser radiation. It has been established that the level of hardening and the ultimate structure of steel are determined by the superposition of stresses, generated in the laser treatment zones, and by the processes of relaxation of the laser radiation energy as a result of local plastic deformation, dynamic polygonization, and recrystallization.