Key Engineering Materials Vol. 1043

Abstract: The use of out-of-furnace desulphurization of cast iron and various dispersed desulfurizing reagents is due to the desire to ensure the most complete removal of cast iron sulfur in the shortest period of time. The actual results of the industrial application of out-of-furnace desulfurization indicate that the practical results and application rates in a number of cases are not stable enough and are far from possible and expected. The studies were carried out on calculated and "cold" transparent physical models. Magnesium, lime, and calcium carbide were evaluated as desulfurizing reagents. Based on the actual results of physical modeling and subsequent calculations, an improved expression was formulated for determining the length of a gas jet in a liquid (L_str ) - the depth of the jet immersion, depending on the parameters of injection through a submerged lance. The processes of interaction between gas and solid phases in the near-lance zone during ladle desulphurization have been studied. It is shown that during the injection desulfurization of cast iron, the gas component of the flow stops its directional movement in the melt for up to 80 mm (practically 50–60 mm), solid particles continue to move in the bubble and hit the surface of this cavity. To assess the further movement of the particle through the "gas cavity-melt" boundary, the depth of penetration of particles into liquid iron was calculated. The motion of a particle in a melt can be described by an equation that is arranged for the conditions of vertical motion of a particle from top to bottom with a given initial velocity up to the complete stop of the particle. Nomograms are given to determine the specified parameters. Recommendations are given on the parameters of injection of magnesium and ground lime.

Abstract: Cobalt-based alloys with nickel and titanium represent a promising class of materials for the development of novel amorphous and high-temperature-resistant alloys. The targeted design of such materials requires detailed knowledge of the thermodynamic properties of liquid alloys. In this work, high-temperature calorimetry was employed to investigate the partial enthalpy of mixing of titanium in the Co–Ni–Ti liquid alloys along the cross-sections x_Co/x_Ni = 3, x_Co/x_Ni = 1/3, and x_Co/x_Ni = 1 at 1873 K and in the concentration range x_Ti = 0–0.6. The partial mixing enthalpy of titanium exhibits negative values, indicating strong interatomic interactions among the components in the melt. The integral mixing enthalpy Δ_mH over the entire compositional triangle was described using the Redlich–Kister–Muggianu formalism. The Δ_mH function shows pronounced negative values, emphasizing the significant role of CoTi and NiTi binary interactions. The associate solution model (ASM) was applied to describe the temperature and composition dependence of the thermodynamic mixing functions in the liquid Co–Ni–Ti alloys. The integral enthalpy Δ_mH, excess entropy Δ_mS^ex, excess Gibbs energy Δ_mG^ex, and Gibbs energy Δ_mG of mixing were evaluated in the temperature range 800–1873 K. It was shown that these thermodynamic functions exhibit increasing negative deviations from ideality upon cooling of the melts. Within the ASM framework, the degree of chemical short-range order in the Co–Ni–Ti liquid alloys was assessed as the total mole fraction of associates Σx_assoc in the solution. It was demonstrated that the Σx_assoc is significant and increases with decreasing temperature. The amorphization composition range for the Co–Ni–Ti liquid alloys was predicted based on our previously proposed empirical criterion related with Σx_assoc. The predicted range of x_Ti ≈ 0.2–0.8 is in satisfactory agreement with known compositions of amorphous alloys in the edged binary systems.

Abstract: The article investigates energy consumption during the drying stage of iron ore pellets, a critical process in ensuring energy efficiency in mining and metallurgical production. Particular attention is given to the influence of charge material moisture content and the application of SAS (SAS) on the specific consumption of energy resources, namely electricity and natural gas. Industrial trials were conducted at one of the leading mining and processing enterprises in the Kryvyi Rih region, focusing on the transition from the baseline (in-house) concentrate to raw material from another regional enterprise, pre-treated with non-ionic SAS. It was established that the increased dispersity and hydrophilicity of the new raw material concentrate necessitate additional moistening of the charge, significantly affecting thermal regimes and energy expenditures during drying. Based on collected experimental data, regression models were developed to quantitatively predict the specific consumption of electricity and gas as a function of technological parameters. The primary factors influencing energy consumption were identified as the moisture content of the charge and the daily throughput of the drying unit. An increase in specific electricity consumption by 17.73% and natural gas consumption by 33.25% was recorded, accompanied by a simultaneous reduction in productivity by 9.55%. The findings are relevant for specialists in energy management, electrical engineering, and thermal analysis in metallurgy, particularly in the development of strategies for optimizing energy consumption under industrial conditions.

Abstract: During underwater wet welding, the environment has a corresponding effect on the mechanical properties of the weld metal. The use of external electromagnetic action (EEA) during welding is promising for influencing the formation of welded joints and the structure formation in physically inhomogeneous environments. Experimental studies have demonstrated the effectiveness of EEA application in reducing the tendency of weld metal to form pores, enhancing degassing, and lowering hydrogen content etc. The paper presents a metallographic study of the welded joint metal of structural steel (St3) after underwater welding with 12Kh18N9T filler wire, both without and with the use of EEA. Based on calculation methods and predictive modelling, optimal operating modes of the electromagnetic system for an experimental study of the EEA effect during underwater welding have been established and implemented. It has been established that the weld metal mainly has a ferrite-pearlite structure, while an austenitic structure with elongated grains is formed in the weld metal. When using the EEA, the grain structure of the weld metal is refined by an average of 1.5 times with an insignificant decrease in microhardness. In the heat-affected zone (HAZ), in the areas of large grain (I HAZ), recrystallisation (II HAZ) and incomplete recrystallisation (III HAZ), a bainitic structure is formed in the presence of ferrite layers. Under the influence of the EEA, the grain size is refined by 1.2 times in the I HAZ and II HAZ with a decrease in the thickness of ferrite layers and an increase in microhardness by an average of 7 ... 10%. The formation of such a structure will provide a set of strength properties and toughness of the welded joint metal. Research has proven that the technology of wet welding under water using the EEA allows for the production of high-quality welded joints with a high set of physical and mechanical properties of the metal of both welded joints and the HAZ.

Abstract: This study investigates the influence of layer thickness and surface condition on the microstructure and mechanical performance of Laser Powder Bed Fusion (PBF-LB) manufactured Ti6Al4V. Specimens were produced using two layer thicknesses, 40~µm and 80~µm, under identical process parameters. Characterization included tensile and axial fatigue testing, supported by microstructural analysis using field-emission scanning electron microscopy (FE-SEM) and electron backscatter diffraction (EBSD). Both processing conditions produced fully martensitic α′ microstructures, with the 40~µm builds showing finer lamellae and smaller prior-β grains due to higher cooling rates. Tensile tests revealed higher ductility for the 40~µm specimens while maintaining similar strength levels. Axial fatigue tests revealed better performance for lower layer thickness, electropolished surface and diagonal orientation. The results confirm that fatigue performance in PBF-LB Ti6Al4V is primarily governed by surface integrity and defect population rather than changes in microstructural morphology. Overall, finer layers and surface finishing enhance endurance strength, though at the cost of reduced build productivity.

Abstract: The mechanical and fatigue behavior of a reactively modified Inconel 625 alloy (IN625-RAM2) produced by Laser Powder Bed Fusion (PBF-LB) was investigated. The alloy achieved near-full density (≈8.30 g/cm³) and exhibited a refined, irregular grain structure with localized equiaxed regions from ceramic-induced nucleation and Zener pinning. It showed high tensile strength (YS 680–770 MPa, UTS 1170–1250 MPa) with modest anisotropy. Under fully reversed loading (R = –1), fatigue limits at 2×10⁶ cycles were 110–122 MPa in the as-built condition and 180–187 MPa after electropolishing, improving fatigue efficiency from ~10% to ~15% of UTS. Compared with reference alloys (AISI 316L, Ti6Al4V, IN718), IN625-RAM2 combined high strength with moderate fatigue resistance, emphasizing the critical role of surface quality in optimizing PBF-LB nickel alloys.

Abstract: In this study, dry, minimum quantity lubrication (MQL) using vegetable-based oil and multi-walled carbon nanotube-reinforced nanofluid-assisted MQL (N-MQL) burnishing conditions and various burnishing speed and depth of burnishing values were used in the sustainable roller burnishing of additively manufactured AlSi10Mg alloy which is widely used in the aviation and automotive industries due to its superior mechanical properties, and burnishing performance was investigated in terms of surface roughness and power consumption. Then, experimental results were evaluated statistically using Taguchi and variance analysis. N-MQL with a burnishing speed of 10 m/min was shown to be the optimum burnishing condition for both surface roughness and power consumption. The optimum burnishing depth was 0.02 mm for power usage and 0.06 mm for surface roughness.

Abstract: This study investigates the microstructural and mechanical integrity of the interface between Wire Arc Additive Manufactured (WAAM) carbon steel (CS) and an S355 structural steel (Wrought CS) plate, with emphasis on the suitability of WAAM for repair and reinforcement of structural components. A wall structure was deposited on a Wrought CS plate using a Cold Metal Transfer (CMT) process and subsequently characterized through microstructural analysis, hardness measurements, tensile testing, and bending fatigue testing. The microstructural observations revealed a smooth and defect-free transition across the interface, consisting of a fine-grained heat-affected zone (HAZ) formed by partial recrystallization. The hardness profile exhibited a continuous gradient, with slightly elevated values near the interface (~210 HV), indicating grain refinement and the absence of softening effects. The tensile results showed that the WAAM-deposited CS possessed higher strength and ductility than the Wrought CS, while the hybrid WAAM CS–Wrought CS specimens displayed intermediate properties. Fracture consistently occurred within the Wrought CS plate rather than at the interface, confirming a metallurgically sound and mechanically robust bond. Under bending fatigue loading, the WAAM CS demonstrated the highest fatigue limit (~250 MPa), followed by the hybrid (~205 MPa) and Wrought CS (~162 MPa). All hybrid specimens fractured on the Wrought CS side, indicating that the interface remained intact under cyclic stress.

Abstract: In this study, CoCrFeNiTi high entropy alloy (HEA) powder was treated by ball milling (BM) for up to 50 hours and sintered compacts were fabricated by spark plasma sintering (SPS). XRD analysis confirmed that the BM powder formed a single BCC solid solution phase after 25 hours, and a nanocrystalline structure was obtained due to the reduction in crystallite size and increase in dislocation density. Meanwhile, after sintering, the main phase changed to FCC, and secondary phases such as CoTi₂, CrFe, and TiC were precipitated. Carbon analysis by EMIA and EPMA showed that the carbon content in the powder and sintered compact increased with increasing BM time, which is considered to be the cause of TiC formation. Micro-Vickers hardness tests showed maximum hardness at the initial state, decreased at 5 hours, and then recovered after 15 hours due to the effect of secondary phase precipitation and microstructure. The effects of BM treatment and sintering conditions on phase structure, microstructure, element distribution, and mechanical properties were clarified, suggesting that it is an effective method for controlling the properties of HEA.