Metallurgist最新文献

The restoration of worn-out parts by electric-arc surface welding using a flux-cored wire with an aluminothermic filler is investigated. The study focuses on a plate made of Hadfield steel (110G13L), a material known for its challenging weldability. The welding process involves depositing three layers onto a preconditioned surface. The surface welding process is mathematically described based on the Prandtl–Reuss model incorporating the Duhamel–Neumann law in place of Hooke’s law and a modified von Mises yield criterion to account for the viscous properties of materials during irreversible deformation. The elastic moduli and yield stress are assumed temperature-dependent. Laboratory studies were conducted to determine the combined thermal effect on the welding process. It is concluded that applying the combined thermal effect during surfacing with flux-cored wire with aluminothermic filler reduces the intensity of residual stresses, thereby enhancing the performance and durability of the welded part.

This paper focuses on the key trends in the production of electrical steel at Novolipetsk Steel (NLMK, Lipetsk, Russia). The work undertaken to enhance the quality of electrical steels at all process stages, from smelting to cutting finished products, and to develop new grades was reviewed. The technologies developed at NLMK to manufacture high-performance electrical steels have improved the quality and ensured the necessary characteristics of rolled steel, including new types of products, and their compliance with customer requirements. To meet current and future market requirements, NLMK Group is engaged in ongoing efforts to improve the quality of electrical steels and develop new high-performance products.

This article presents the hot rolling process of a substrate for the production of cold-rolled hot-dip galvanized steel with an inverse temperature gradient using a continuous wide strip mill 2000. The average acceleration of the main part of the strip was increased by 60% relative to the acceleration under the standard mode, which ensures a constant finishing temperature. The physical and mechanical properties of samples collected along the length of the strip were found to comply with the requirements for the strength and plastic characteristics of metals outlined in normative documentation. We established that the hot rolling mode with increased acceleration in a finishing train results in a reduction of machine time of 3–11%, depending on the unit size of the processed metal.

The article considers how the disturbing factor of equipment components in temper mills, the thickness variation of a substrate, the instability of strip tension, backup roll runout, and other factors influence the reproduction coefficient of surface microgeometry of work rolls onto the temper-rolled strip, and consequently, the variation of microgeometry parameters of strip surface on its separate sections. These fluctuations in the reproduction coefficient are qualitatively estimated, with their percentage contribution to the total disturbing factor in the temper-rolling process being established. We demonstrate that the backup roll runout exerts the most significant influence on the instability of the reproduction coefficient, which accounts for 38 to 45%. The findings are illustrated using the example of temper mill 1700 at Magnitogorsk Iron and Steel Works (MMK, Magnitogorsk, Russia), which indicates that at low levels of all disturbing factors, the fluctuation in the parameter Ra of the temper-rolled strip is 5.8%, reaching 9% at higher levels.

Research and development of new intermetallic materials and alloys with a unique set of physical, mechanical, and operational characteristics, as well as improvement of their production processes are very important. The established techniques of producing iron-aluminum intermetallic alloys, used commercially as wear-resistant and anti-corrosion coatings, typically involve the use of multi-stage energy-consuming processes, which largely determine the high cost of the final product. A significant reduction in the number of operations and energy costs is achieved by using a single-stage process for producing intermetallic compounds of the Fe-Al system, such as aluminothermic remelting of thermite charge components that include iron scale and a reducing agent containing active aluminum. The high process temperature significantly reduces the time required to form a liquid phase and complete the interaction of the low-melting components with iron, thereby ensuring their significant content in the final iron-aluminum alloy. The paper presents the results of an experimental study of the effect of the amount of active aluminum in the thermite charge on the structure and microhardness of experimental iron-aluminum alloys formed as a result of exothermic remelting of the charge in a graphite reactor.

A comparative analysis of the effect of aging temperature in the interval of 175–250 °C as well as holding time on the stability of the achieved hardening and structural evolution of the aging products (θ′-phase particles) is carried out for experimental wrought Al–6Cu–0.5Mn, Al–6Cu–0.5Mn–0.1Sn, and Al–6Cu–0.5Mn–0.1Sn–0.2Si alloys having tin and silicon micro additions in their compositions. Experimental studies into the structure are conducted using the methods of electronic scanning and transmission microscopy, while studies of physical and mechanical properties are conducted by analyzing changes in hardness (HV) and specific electrical conductivity during isothermal aging of alloys obtained in the form of flat products. A micro addition of tin significantly increases the peak hardness of alloys in the entire studied interval of aging temperatures. The increase in temperature of up to 250 °C, compared to aging at a lower temperature of 175 °C, leads to a natural decrease in the peak hardness of the studied alloys, although to varying degrees. The peak hardness of tin-containing alloys decreased only by 10% (up to 140 HV) compared to 18% (up to 110 HV) in the base Al–6Cu–0.5Mn alloy. A gradual decrease in hardness of all alloys at different rates after achieving peak hardening during prolonged holding and aging at 250 °C is shown. At the same time, the rate of decrease in hardness of the Al–6Cu–0.5Mn–0.1Sn–0.2Si alloy with a silicon micro addition during ongoing annealing is significantly lower than that of other two alloys. An analysis of the microstructure showed that the proportion of more dispersed particles is significantly higher in the Al–6Cu–0.5Mn–0.1Sn–0.2Si alloy with a silicon micro addition compared to that in the Al–6Cu–0.5Mn–0.1Sn alloy. This circumstance may explain the observed higher hardness of the alloy with a small silicon addition after long-term high-temperature annealing.

We develop a technology for the production of iron oxide-pigment and nickel concentrate from the sludges of acid decomposition of serpentinite. We study the chemical and phase compositions of the polymetallic sludge obtained as a result of cleaning of the magnesium-chloride solution performed after the acid decomposition of serpentinite from the Bazhenov deposit. It is shown that the predominant element in the composition of sludge is Fe, and its weight fraction recalculated to iron (III) oxide is 53–56%. The weight fraction of Ni in the polymetallic sludge attains 1.3%. It is experimentally demonstrated that the procedure of selective leaching seems to be the most acceptable method for separating elements in the polymetallic sludge. The maximum degree of nickel (II) extraction equal to 96–99% is observed for pH = 1.4–1.5 at a temperature of 80 °C and a concentration of the HCl solution equal to 20 wt%, while the degree of extraction of iron (III) into the solution does not exceed 7%. A technological scheme of processing of polymetallic sludges is developed. The degree of nickel (II) extraction into the solution is 98%. The obtained iron-oxide pigment contains 93 wt% Fe₂O₃. The remaining qualitative characteristics of the pigment are comparable with the characteristics of the YIPIN S130 (China) pigment.

Composite coatings were obtained by detonation spraying of copper–chromium powder mixtures with varying particle sizes onto steel substrates. The mixtures used contained 50 wt. % chromium. The microstructure of the coatings was analyzed using light microscopy, scanning electron microscopy, and X-ray diffraction analysis. The microhardness and electrical resistivity of the resulting samples were measured. The phase composition of the coatings consisted of α‑Cu and β‑Cr. The chromium content in the coatings was reduced by 8–12 wt. % compared to the initial powder mixtures. The most uniform distribution of chromium particles in the copper matrix was observed when spraying mixtures consisting of 20–40 or 40–60 μm copper particles along with 20–40 μm chromium particles. The microhardness of these coatings is twice that of copper obtained by hot rolling. This is attributed to the influence of solid chromium particles, formation of a fine structure, and an increase in the density of defects in the crystal lattice of materials during detonation spraying. The electrical resistivity of the coatings is comparable to that of other materials with similar composition obtained by sintering and cladding methods.

The study shows the effect of electron-beam treatment on the surface structural state and properties of a monolithic TiNi-based alloy. Initial monolithic TiNi alloy plates with a surface oxide layer were obtained by vacuum induction melting and subsequent rolling of ingots. Electron-beam treatment of the samples was carried out at an energy density of 3.5 and 4.5 J/cm², and a pulse count was 15. The structural and phase composition of the plate surface before and after the electron-beam treatment were studied using X‑ray diffraction analysis, optical and scanning microscopy, and interference profilometry. The wettability parameters were determined using a droplet shape analyzer based on the contact angle value. The roughness parameters were also assessed. It has been established that the exposure to electron-beam treatment changes the structure and phase composition by increasing its homogeneity. Increased electron energy during electron-beam treatment makes it possible to reduce the surface roughness parameters, leading to an increase in the contact angle of wetting. The characteristic temperatures of martensitic transformations remain practically unchanged.

This study present the results of test rolling of narrow strips made of S1 lead alloy on a 130 × 10 two-high mill, along with methods for improving the quality of rolled products. The dimensional changes of strips with an initial thickness of 2 mm and a width of 10 mm were investigated during six-pass rolling to a final thickness of 0.9 mm. After rolling, the transverse wedge of the strip edges was found to range from 0.02 to 0.03 mm, exceeding the allowable limits. It was demonstrated that as the draft increases from 30 to 50–55% from pass to pass, the transverse thickness variation decreases from 0.05 to 0.02 mm. Linear regression equations were derived to predict the effect of the number of passes on the transverse profile and the wedge angle. Measurements revealed that the upper side of the top roll, which is not fixed in the housing, is elastically deformed by about 0.03 mm, resulting in uneven pressure distribution over about 4 mm along the roll body. This uneven pressure causes nonuniform transverse deformation of the strip during rolling. The study also examined the effect of uneven transverse deformation on strip hardness, revealing a hardness variation from 50 to 58 HV across the width. Linear regression equations were derived to predict the relationship between strip hardness and thickness for a rolled S1 alloy strip. Based on the findings, a rational profile for the top roll was proposed to eliminate the irregularities of transverse deformation. The improved technology and equipment enable the production of high-quality S1 alloy strips on the two-high mill of the Bogorodsky Branch of the NPO Pribor machine-building company.