Key Engineering Materials Vol. 1041

Abstract: Relevance of the work. One of the key challenges currently faced by manufacturers of steel wire rod for welding applications worldwide is achieving maximum plasticity in the metal before delivery to hardware plants. This need arises due to the ongoing technological advancements in hardware plants and the integration of modern equipment capable of producing wire at high drawing speeds with significant degrees of unit deformation. Such processes demand high-quality raw materials (wire rod). Another crucial aspect is ensuring a high-quality surface for the welding wire, free from microcracks and hard inclusions. These defects can negatively impact the welding process by increasing metal spatter, causing electric arc instability, and leading to critical defects in welded joints, such as cavities and cracks. Rational microstructural design is a key principle in producing highly plastic wire rod for the efficient manufacturing of solid-section welding wire from low-carbon alloy steels. The presence of hard components (such as martensite, bainite, or their mixtures) in the wire rod’s structure is undesirable, as they increase the risk of metal failure during intensive cold deformation by drawing. Minimizing these hard phases remains an urgent scientific and practical challenge. The aim of the study is to determine the mechanism of martensite grains formation during slow cooling of low-carbon alloy steel grade CrMoV1Si wire rod, used for producing welding wire, from the austenitization temperature to room temperature. Material and methodology. The material used in this study was steel with the chemical composition (in wt.%) 0.08C–1.30Mn–0.54Si–1.06Cr–0.54Mo–0.24V–Fe_(balance). The samples were subjected to thermal cycles using an automated Gleeble 3800 thermal deformation simulation system. The thermal cycle involved heating the samples to the temperature required for complete austenitization, holding them at this temperature, and then continuously cooling at controlled rates of 0.20, 0.10, and 0.05 °C/s to room temperature. Metallographic analysis was conducted using an optical microscope and a scanning electron microscope. The hardness of individual structural components was measured using a microhardness tester following the standard method. The chemical composition of the phases was determined by energy-dispersive X-ray spectroscopy and Auger electron spectroscopy. Results. The study established an anomalous increase in the volume fraction of austenite shear transformation products in CrMoV1Si steel after continuous slow cooling at rates of 0.20–0.05 °C/s, at the same time, martensite had a relatively high carbon content (up to 1.6 wt.%). The authors attribute this microstructural evolution to dynamic changes in the chemical composition of individual phases during cooling, primarily due to the partitioning of carbon and other alloying elements between the α and γ phases, as confirmed experimentally. Based on the obtained results, a mechanism has been proposed for the formation of high-carbon martensite grains in low-carbon alloy steel wire rod during slow cooling from the austenitization temperature to room temperature.

Abstract: The microhardness of CoCrFeNiMnV_x (х = 0-2) high-entropy alloys (HEAs) was measured in the temperature range 77-293 K. At x ≤ 0.4, a significant monotonic increase in microhardness occurs with decreasing temperature, which indicates the thermally-activated character of plastic deformation of the material under the indenter. At x = 0.5, as well as at x = 0.75 and 0.85, athermal behavior of microhardness was detected in the ranges of 200-293 K and 150-293 K, respectively. The latter is apparently associated with the appearance in the indicated alloys, along with the FCC phase, of precipitates of the hard intermetallic sigma phase, which are athermal obstacles to the motion of dislocations. For the first time the microhardness of the sigma phase in the range of 77-293 K was measured; at 293 K and 77 K it was about 9.5 GPa and 12.5 GPa, respectively, which is approximately 5 times higher than the microhardness of the FCC alloy with x = 0.25.

Abstract: At temperatures of 290 K and 77 K, the phase composition and mechanical properties ofnonequiatomic medium-entropy (MEA) alloys Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 werecompared in the coarse-grained (CG) and nanostructured (NS) states, in which additionaldeformation mechanisms are activated under load: phase transformations in the MEAFe50Mn30Co10Cr10 (MEA TRIP) and twinning in the MEA Fe40Mn40Co10Cr10 alloy (MEA TWIP). Itis shown that in the NS state in both alloys, in contrast to the CG state, a complete phase transitionfrom the fcc to the hcp phase is observed, the content of which weakly depends on the temperatureand the number of torsion revolutions during high-pressure torsion (HPT). The transition from theCG to the NS state leads to an increase in the microhardness (in the NS MEA TWIP by 3.7 and inthe NS MEA TRIP by 2.25). In the CG state, a thermally activated character of plastic deformationis observed for both alloys in the temperature range of 290 – 77 K. In the NS state, MEA TWIPremains plastic under active compression deformation at 290 K and 77 K, whereas in NS MEATRIP under similar conditions, macroscopic plasticity is absent. Tensile deformation up to 50 % at30 K in the CG state for both alloys leads to a significant decrease in the absolute values of Young'smodulus over the entire temperature range.

Abstract: Actuality. LPBF (laser powder layer fusion) is a modern additive manufacturing technology that allows you to quickly and accurately manufacture complex metal parts with minimal material waste. The study of single tracks formed during local melting of powder by a laser is a key method for optimizing process parameters and verifying the operation of 3D printers. This approach remains relevant due to the influence of technical features of the equipment, protective gases and chemical composition of materials, as well as for expanding the knowledge base on the crystallization processes of known alloys. Objective of the study: An experiment was conducted in the format of single tracks using 60 combinations of technological modes in 13 positions on the build platform. The analysis used optical microscopy methods after chemical etching (Culling reagent No. 2) and statistical data processing using polynomial regression. Results. It was found that the key influence on the depth and width of the melt pool is the scanning speed, while the power acts more linearly. The microstructure features depending on the position on the platform were revealed, which is associated with optical deviations of the laser beam from the vertical axis. Conclusion. The results obtained allow us to determine the technological window for the formation of defect-free tracks and contribute to the optimization of processes in laser additive manufacturing.

Abstract: Food-grade piping and water transportation systems extensively use dissimilar welding between stainless steel and carbon steel, where cost-effectiveness and corrosion resistance are essential consideration. However, the fusion zone of dissimilar welds often observed microstructural inhomogeneities and hardness changes, thus compromising mechanical qualities and corrosion resistance. This study was seperated in two phases to investigate and optimize dissimilar welding between carbon steel and stainless steel in both plate and pipe applications. Phase 1 studied welding A36 carbon steel plate and A304 stainless steel using gas tungsten arc welding (GTAW) with ER308L filler metal, the effect of post-weld heat treatment (PWHT) holding time on the mechanical and microstructural propertie. PWHT was performed at 650 °C for 20 and 60 minutes. The 20-minute condition yielded an optimal combination of mechanical strength and microstructural refinement, while the 60-minute condition led to grain coarsening and reduced strength. Phase 2 extended the findings to pipe welding applications, adopting the 20-minute PWHT condition. Welding was performed on dissimilar joints between A106-B carbon steel pipe and A312 TP304L stainless steel pipe (2-inch OD) using ER308L and ER309L filler metals under 99.99% argon shielding. Tensile and hardness testing indicated that welds with ER309L offered superior mechanical performance. Microstructural analysis revealed delta-ferrite and stabilized austenite in the fusion zone, with enhanced Cr and Ni concentrations contributing to improved corrosion resistance, as confirmed by electrochemical testing.

Abstract: Quasicrystalline ingots of the following compositions were obtained and studied: Al₆₃Cu₂₅Fe₁₂; Al_62.735Cu₂₅Fe₁₂Sc_0.265; Al_62.56Cu₂₅Fe₁₂Sc_0.44. It is shown that 0.01% Sc is contained in the icosahedral quasicrystalline phase (Al_65.1Cu_22.57Fe_12.33Sc_0.01). In addition to this scandium is contained in the intermetallic Al_51.45Cu_37.29Sc_8.23 (hexagonal W phase). It is established that alloying of the quasicrystalline Al-Cu-Fe alloy with scandium in the amount of 0.44 at. % significantly increases the content of the quasicrystalline icosahedral phase in ingots from 50 to 65 vol.% which leads to an increase in the microhardness of ingots. The microhardness of Al-Cu-Fe quasicrystalline ingots in the range of 20 - 400 °C is weakly dependent on temperature and amounts to 7-8 GPa. With increasing temperature, the microhardness value begins to decrease and at 720 °C reaches a value of 0.5 GPa. The study of the electrochemical characteristics of the corrosion process of quasicrystalline ingots showed that alloying of Al-Cu-Fe quasicrystalline alloy with Sc decreased the corrosion rate of non-annealed samples, and simultaneously lowered both the corrosion potential and the pitting potential.

Abstract: Phase components of experimental low cost titanium alloys, their substructure and parameters, dislocation structure, features of phase formation in the metal, which differ in alloying systems, were studied using complex research methods. The stoichiometric composition of dispersed phases in the internal volumes of alloy grains was determined by diffraction patterns using transmission electron microscopy. It is shown that in the structure of titanium alloy Ti-2,8Al-5,1Mo-4,9Fe there are dispersed nanoparticles of intermetallic phases of different morphology and stoichiometric composition. These are the phases: Ti₃Al and Fe₂Ti with a size of 10…40 nm; Mo₉Ti₄ - 20…120 nm. Studies of titanium alloy Ti-1,5Fe-O showed the presence in the structure of mainly nanoparticles of oxides: Ti₃O₅ size 10…30 nm and Ti₄Fe₂O, FeTiO₅ (10…90 nm), as well as intermetallics Fe₂Ti (10…40 nm). It is established that the formation of nanoparticles of intermetallic and oxide phases in the thin plate structure of the investigated experimental low cost titanium alloys promotes the formation of the substructure with uniform distribution of dislocation density. This provides a high level of mechanical properties of alloys.

Abstract: This study aimed to smelt high-entropy alloys (HEAs) composed of inexpensive and commonly available metallic elements using iron-based alloys, ligatures, and commercially pure metals, and to investigate their phase structure and heat-resistance. High-entropy alloys of the FeNiCrCuAl system were smelted in air using an induction furnace with a crucible lined with rammed neutral aluminum and magnesium oxides. The elements Fe, Ni, Cr, Cu, and Al were introduced via high-alloy cast iron, stainless steel grade GX10CrNiMn-18-9-1 (1.4541), industrial-grade low-carbon ferrochrome (FeCr70C1), binary Cu-33Al ligature, tough-pitch copper, and semi-finished nickel. Samples of the investigated alloys were prepared using lost foam and sand mold casting methods. Microstructural analysis revealed the presence of rounded dendritic branches, copper-rich interdendritic regions, and high-chromium carbides. The phase composition of the as-cast FeNiCrCuAl alloys consisted of multiple phases: solid solutions with a BCC structure ordered in the B2 type, an FCC structure, and complex carbides (FeCr)₇C₃. High-entropy alloys of the FeNiCrCuAl system, with increased aluminum and chromium content, can significantly outperform standard heat-resistant stainless steels in terms of oxidation resistance indicators – surface oxidation rate, and oxidation stability at 900°C and 1000°C. The specific oxidation of the high-entropy alloy FeNiCrCuAl, which contains at least 18 at. % chromium, was 0.1627 mg/cm² after a 4-hour exposure at 1000 °C. Under the same conditions, the specific oxidation of X2CrNi19-11 stainless steel (1.4306) was 0.6689 mg/cm².

Abstract: This study assessed the quality of recycled aluminum pots produced through artisanal processes in Cameroon. The objectives were to identify production practices, analyze the chemical composition of finished products, and evaluate the process capability to comply with food safety standards. Results revealed a high variability in practices across regions, with a predominance of non-compliant practices. Notably, lead content significantly exceeded regulatory limits in 66.6% of samples, with levels reaching up to 0.152%. This contamination was primarily attributed to the lack of rigorous waste sorting, the introduction of foreign materials during melting, and a lack of quality control. Process capability analysis revealed very poor performance, with less than 3% of products meeting standards. These findings highlight the urgent need for measures to improve product quality and ensure compliance with regulatory requirements.