Metallurgist最新文献

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.

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.