Metallurgist最新文献

This article presents an overview of the technology employed in the production of special types of coke obtained from non-sintering coals sourced from Kazakhstan. The microstructure of special types of coke is elucidated, and the effect of the heating rate on their microstructure and properties essential for use as a reducing agent in electrothermal processes for the production of technical silicon metal is studied.

The possibility of partial replacement of Ge by Si within the structure of Bi₁₂GeO₂₀ during synthesis from a melt by a casting method is demonstrated. The effect of substitution on the structure of synthesized polycrystalline material is studied. Using X‑ray phase analysis and optical microscopy, it is confirmed that stable bismuth silicate and germanate with a sillenite structure form a continuous series of solid solutions. The possibility of partial replacement of Ge by Si within the structure of Bi₁₂GeO₂₀ during its synthesis from a melt by accelerated cooling (casting method) is demonstrated.

Based on the theory of full and complex compensation, taking into account the charge and technological conditions, the article presents calculations of promising modes of blast furnace smelting with injection of pulverized coal fuel in an amount exceeding 200 kg/t of cast iron.

Influence of boron in a wide content range (0.0004–2.0%) and its joint effect with other alloying elements (Ti, Ce, Nb, Si, Mo, W, Al, N) on the structure and properties of austenitic stainless steels was analyzed. Due to segregation of boron along the grain boundaries and formation of various carbides, it is capable of increasing the strength and ductility, creep resistance and performance properties at high temperatures (> 600 °C). At the same time, a small boron content (≤ 0.004%), for example, in grade 304 stainless steel (Russian analogue—steel 08Kh18N10), leads to an improved corrosion resistance. However, with an increase in boron content (up to 2%), the positive effect disappears and steel becomes more susceptible to corrosion, while becoming stronger and inhibiting cracks formation during deformation due to grain refinement.

This article presents the results of the modeling of the behavior of the titanium alloy Ti-3Al‑2.5V at the initial stage of extrusion of a tube billet. The influence of the gaps between the surfaces of the tool and the billet on the nature of its shape change and the strain state is discussed. In particular, the most deformed tube parts of the maximum (by modulus) strain tensor values are identified. The dependence of the Ti-3Al‑2.5V alloy tube extrusion force on the stroke of the pressure pad is calculated. The results of the calculation of the maximum forces and the forces at the steady-state stage are in good agreement with the data obtained under an industrial experiment. Horizontal extrusion leads to an asymmetry in the location of the deformation fields relative to the extrusion axis. Accordingly, an asymmetric distribution of properties arises in the extruded tube, which is experimentally confirmed using hardness measurements. Correspondence is established between the simulation data on the heterogeneity of the strain distribution over the wall thickness of the hot-pressed tube made of titanium alloy Ti-3Al‑2.5V, considering the pressing-out, with the results of micro- and X‑ray structural studies of the tube semifinished product obtained.

Screw rolling is widely used in manufacturing seamless pipes and solid round products. In any operating helical rolling mill, deformation occurs under the influence of intrafocal axial compression (i.e., with backing), leading to significant transverse deformation. Consequently, metal shaping occurs under conditions of sign-variable radial deformation, which consumes a significant part of the power expended during rolling. As a result, the implementation of the rolling process under the influence of intrafocal axial extension (i.e., with tension) creates the most favorable conditions for the flow of metal in the deformation zone. The proposed technological solution opens up prospects for the use of swaging and rolling mills for screw rolling in producing continuous rolled products and specialized pipes in a wide range of sizes and grades. This article presents the results of the first experimental testing of a new helical rolling process performed on a mini-mill 14–40 under the conditions of the research and production center of the Department of Mechanical Engineering of the National University of Science and Technology “MISIS.” The experiment confirmed the operability of the new technology of helical rolling as a whole. The results obtained during experimental rolling showed that the specific power expended on the deformation of a unit volume, depending on the total reduction, was reduced by 25.4–37.3%, whereas the transverse deformation of the rolled billet was significantly reduced.

The results of the inspection of mechanical properties were provided for very-thick-walled shells (D/S ≈ 3.06 and D/S ≈ 3.1) made from T‑grade steel wheel manufactured by screw piercing using experimental and industrial two-high mill MISiS 130D with the feed angle β = 12°/μ = 1.26 and β = 14°/μ = 1.36. A comparison of the obtained results of mechanical properties showed that the piercing process with a larger feed angle (i.e., β = 14°/μ = 1.36) is more preferable than the piercing process with β = 12°/μ = 1.26 to improve the properties of initial hollow billets. The analysis of the dimensions of very-thick-walled shells made from steel wheel with the ratio of D/S ≈ 3.1 manufactured by piercing using the screw rolling mill MISiS 130D showed high precision, with outer diameter deviation ∆D = (−0.1 mm; +0.3 mm), inner diameter deviation ∆d = (0 mm; +0.4 mm), and wall thickness deviation ∆S = (−0.3 mm; +0.2 mm). When manufacturing hollow billets made from axle steel to manufacture hollow car axles using the industrial pipe rolling mill 70-270 (Vyksa Steel Works), we registered the positive effect of the screw piercing process (β = 12°/μ = 1.3) on strength, plastic properties, and impact strength, that is, relative elongation (δ; initial/as-pierced condition) was 38.9%/41.9 MPa and impact strength KCU⁺²⁰ was 63.3/72 J/cm².

Based upon the Al-Cu-Mn system, aluminum hypoeutectic heat resistant aluminum alloy of the Al₄Cu₂Mn_0.5Ca_0.2Zr (wt. %) (P2) composition is developed, synthesized, and studied. An effect of increasing thermal stability is achieved due to nanosize dispersed intermetallics Al₂₀Cu₂Mn₃ and Al₃Zr, and also with addition of eutectic-forming elements, whose role is played by calcium. It is established that reserves of alloying an aluminum matrix within piston silumin is almost exhausted by the limit of silicon, copper and manganese solubility within aluminum solid solution. In order to substantiate the piston silumin P1 chemical composition a calculation is made for the phase composition of the Al-Si-Cu-Mg-Ni-Fe-Mn system by means of Thrmoclac software. Welded alloy microstructure is studied by means of electron microscopy (SEM) and X-ray microanalysis (XRMA). Vickers hardness of the alloy proposed P2 and equivalent piston silumin P1 is compared in the original condition and after annealing at 250 and 400 °C with a step of 50 °C, as a result of which alloy P2 developed retains more effectively hardness on heating, than for alloy P1, being potentially more heat resistant.

The article is devoted to the complex challenges associated with the development of welding wire for welding high-strength steel in shielding gases.

In the development of welding wire, it is essential to address a number of considerations related to the resistance of welded joints to hot and cold cracking, wire production technology, the regulatory level of mechanical properties, the manufacturability of the welding process, and the environmentally friendly working conditions of welders. These factors should be taken into account when determining the chemical composition of the wire. This is a challenging and multifactorial task related to optimizing the chemical composition of the wire in order to ensure compliance with all of the aforementioned requirements. The formation of cold cracks in welded joints of steels that have undergone electroslag remelting can be prevented by increasing the austenitic stability of the weld metal. This can be achieved by increasing the nickel content in the welding wire. However, this results in a decrease in the resistance of the weld metal to the formation of hot cracks and a reduction in hot ductility. This makes the technology of metal rolling for wire manufacture more challenging. To enhance the resistance of the weld metal to the formation of hot cracks, it is necessary to increase the chromium content in the welding wire. However, this approach results in an increase in the ferritic phase within the weld, which subsequently leads to a reduction in the resistance of the welded joint to the formation of cold cracks. The results of the research on the effect of the chemical composition of welding wire, when varying the Cr_eq/Ni_eq ratio, on the indicators of technological strength were used to optimize the composition of the new welding wire. The experimental data on the properties of welded joints of high-strength steels made with a new welding wire demonstrated an advantage over serial joints manufactured with the Sv-08Kh20N9G7T grade wire. Furthermore, the studies of the welding aerosol showed a 6.6-fold reduction in the content of toxic manganese oxides when welding with the new wire in comparison to the conventional Sv-08Kh20N9G7T.