Search Results (96)

To address the performance degradation associated with retained high-temperature δ-ferrite in welded joints of high-silicon 20Cr11W2VTaSi steel—a candidate structural material for spallation targets in Accelerator Driven Subcritical Systems—this study systematically investigates the microstructural evolution and mechanical behavior of 20 mm-thick forged joints produced via automated tungsten inert gas (TIG) welding using a 7° U-groove narrow-gap configuration. Results demonstrate that the narrow-gap process—featuring reduced filler metal deposition and low heat input—is believed to suppress macrosegregation of ferrite-stabilizing elements (e.g., Cr, Si, Mo). As a result, the δ-ferrite content in the weld metal is constrained, exhibiting a fine, dispersed, worm-like morphology embedded within a uniform matrix of tempered martensite. Microhardness mapping confirms homogeneous hardness distribution across the joint, closely matching that of the base metal, with no statistically significant localized softening zones identified. Mechanical characterization reveals an optimal balance of strength and toughness: the joint achieves a room-temperature tensile strength of 820 MPa and retains 436 MPa at 550 °C; moreover, the Charpy impact energy at the weld center reaches 171.2 J. Full article

With the strategic shift toward reducing reliance on critical raw materials, Cobalt-free eutectic high-entropy alloys (EHEAs) have emerged as a pivotal frontier for high-performance structural applications. This review systematically elucidates the synergistic relationship between Co-free alloy design and the non-equilibrium solidification mechanisms of Selective Laser Melting (SLM). The ultra-high cooling rates (10⁵–10⁸ K/s) inherent in SLM are shown to refine eutectic lamellae to the sub-micron scale (typically <300 nm), effectively suppressing the macro-segregation common in conventional casting. We evaluate the design principles of Al-Cr-Fe-Ni and related systems, noting that SLM-processed Co-free EHEAs frequently achieve yield strengths exceeding 1000 MPa and ultimate tensile strengths (UTSs) surpassing 1300 MPa, while maintaining tensile elongations above 10%—a significant improvement over the coarse-grained structures produced by traditional methods. Furthermore, the study identifies critical processing windows, such as laser energy densities (60–120 J/mm³), required to mitigate micro-cracking and achieve near-full density (>99.5%). By synthesizing recent experimental breakthroughs and AI-driven modeling, this review provides a quantitative roadmap for the precision manufacturing of cost-effective, high-performance EHEAs, bridging the gap between theoretical alloy design and industrial additive manufacturing. Full article

Vacuum arc remelting (VAR) is essential for producing premium titanium alloys, where an externally applied alternating magnetic field enables circumferential stirring to control ingot homogeneity. However, current magnetic field parameter design relies on empirical trial-and-error approaches, lacking systematic theoretical guidance. To address this issue, this study establishes a comprehensive multi-physics framework through a two-dimensional axisymmetric swirl model integrating electromagnetic, fluid dynamics, thermal, and solute transport phenomena. Our findings demonstrate that both the magnetic field strength and period exhibit optimal operating ranges, which directly influence ingot homogeneity. As magnetic field strength increases progressively, ingot uniformity shows a distinctive non-monotonic response—initially improving before subsequently deteriorating. Correspondingly, with increasing stirring period, macrosegregation undergoes a distinct three-stage evolution: initial mitigation, subsequent aggravation, and final alleviation. These phenomena originate from the small-scale circulatory flow generated by the external magnetic field on the surface of the VAR molten pool. The interactions among the flow, the solute diffusion layer, and the mushy zone collectively alter elemental diffusion behavior, ultimately determining the homogeneity of the ingot. This study provides a theoretical foundation for precise control of ingot homogeneity in titanium alloy VAR processes and demonstrates significant potential for engineering applications. Full article

Macrosegregation in continuous casting slabs remains a critical defect that adversely affects the homogeneity and mechanical properties of the final rolled products. Industrial experiments were conducted on E355 steel continuous casting slabs to investigate the effects of electromagnetic stirring (EMS) and soft reduction (SR) on the evolution of slab macrosegregation. Furthermore, the inheritance of segregation from the slab to the rolled plate was analyzed. The results indicate that the equiaxed crystal ratio increases and the centerline segregation decreases with increasing stirring intensity. The application of both secondary EMS and SR minimized the centerline segregation in the slab. When the current intensity was increased from 0 A to 320 A in continuous stirring mode, the equiaxed crystal fraction increased from 22.52% to 32.52%, and the centerline segregation index decreased from 1.23 to 1.17. Compared with the continuous stirring mode, the alternating stirring mode promoted a more pronounced increase in the equiaxed crystal ratio and a further reduction in the centerline segregation. The centerline segregation in the slab correlates with the banded structure observed in the rolled plate. A higher degree of slab centerline segregation corresponds to a more severe banded structure and greater fluctuations in the mechanical properties of the plate. Through parameter optimization, the recommended settings are an alternating stirring mode with a current of 320 A at 5 Hz and an SR amount of 3 mm. Under these optimized conditions, the equiaxed crystal ratio of the slab increased to 35.22%, the centerline segregation index dropped to 1.15, and the banded structure in the rolled plate was reduced to grade 2.0. Consequently, the standard deviations of the tensile strength and elongation were 8.03 MPa and 1.1%, respectively. Full article

Some cast metallic alloys for ultra-high-temperature structural applications can have better mechanical properties compared with Ni-based superalloys. Research on the directional solidification (DS) of such alloys is limited. The production of DS components of these alloys with “tailor-made” microstructures in different parts of the component has not been considered. This paper attempts to address these issues. A bar of the RCCA/RM(Nb)IC with nominal composition 3.5Al–4Crc6Ge–1Hf–5Mo–36Nb–22Si–1.5Sn–20Ti–1W (at.%) was directionally grown using OFZ processing, where the growth rate R increased from 1.2 to 6 and then to 15 cm/h. The paper studies how the macrosegregation of the elements affected the microstructure in different parts of the bar. It was shown that the synergy of macrosegregation and growth rate produced microstructures from the edge to the centre of the OFZ bar and along the length of the OFZ bar that differed in type and chemical composition as R increased. Contamination with oxygen was confined to the “root” of the part of the bar that was grown with R = 1.2 cm/h. The concentrations of elements in the bar were related (a) to each of the parameters VEC, Δχ, and δ for different sections, (i) across the thickness and (ii) along the length of the bar, or to each other for different sections of the bar, and demonstrated the synergy and entanglement of processing, parameters, and elements. In the centre of the bar, the phases were the Nb_ss and Nb₅Si₃ for all R values. In the bar, the silicide formed with Nb/(Ti + Hf) less or greater than one. There was synergy of solutes in the solid solution and the silicide for all R values, and synergy and entanglement of the two phases. Owing to the synergy and entanglement of processing, parameters, elements, and phases, properties would “emerge” in each part of the bar. The creep and oxidation properties of the bar were calculated as guided by the alloy design methodology NICE. It was suggested that, in principle, a component based on a metallic UHTM with “functionally graded” composition, microstructure and properties could be directionally grown. Full article

This paper presents the detailed comparisons of solute macro-segregation pictures predicted by different meso-macroscopic simulations, based on the single-domain enthalpy–porosity approach coupled with distinct models of flow resistance in the two-phase zone. In the first, the whole zone is treated as a Darcy’s porous medium (EP model); in the other two, the columnar and equiaxed grain structures are distinguished using either the coherency point (EP-CP model) approach or by tracking a virtual surface of columnar dendrite tips (EP-FT model). The simplified 2D model of a solidifying cast in a centrifuge is proposed, and calculations are performed for the Pb-48wt. % Sn cast at various hypergravity levels and rotation angles. It is shown, in the example of Sn-10wt. % Pb alloy, that the predicted macro-segregation strongly depends on the mesoscopic model used, and the EP-FT simulation (validated with the AFRODITE benchmark) provides the most realistic solute inhomogeneity pictures. The EP-FT model is further used to investigate the impact of the hyper-gravity level and the cooling direction on the compositional nonuniformity developing in centrifuge casting. The hyper-gravity level visibly impacts the macro-segregation extent. The region of almost uniform solute distribution in the slurry zone rises with the increased effective gravity, though the solute channeling is more severe for higher gravity and rotation angles. A-channeling and V-channeling were observed for angles between the gravity vector and cooling direction lower than 120° and higher than 120°, respectively. Full article

A simple Lagrangian travelling slice model has been successfully used to predict the relations between the process parameters and the strand temperatures in the continuous casting of steel. The present paper aims to include a simple macrosegregation, grain structure and mechanical stress and deformation model on top of the thermal slice framework. The basis of all the mentioned models is the slice heat-conduction model that considers the complex heat extraction mechanisms in the mould, with the sprays, rolls, and through radiation. Its main advantage is the fast calculation time, which is suitable for the online control of the caster. The macroscopic thermal and species transfer models are based on the continuum mixture theory. The macrosegregation model is based on the lever rule microsegregation model. The thermal conductivity and species diffusivity of the liquid phase are artificially enhanced to consider the convection of the melt. The grain structure model is based on cellular automata and phase-field concepts. The calculated thermal field is used to estimate the thermal contraction of the solid shell, which, in combination with the metallostatic pressure, drives the elastic-viscoplastic solid-mechanics models. The solution procedure of all the models is based on the meshless radial basis function generated finite difference method on the macroscopic scale and the meshless point automata concept on the grain structure scale. Simulation results point out the areas susceptible to hot tearing. Full article

This paper presents the changes in microstructure and mechanical properties that occurred across the wall cross-section of a massive slag ladle casting due to service conditions. The slag ladle was made of low-carbon cast steel. Based on the test results, it was shown that the working environment influenced the macro-segregation of C and S on the cross-section of the wall and, consequently, had an effect on the changes in microstructure. A pearlitic–ferritic microstructure was found in the central part, while in the outer and inner parts of the wall, the microstructure was of a ferritic–pearlitic type. This change mainly influenced the impact energy—the lowest values were obtained at the centre of the wall (24 J at +20 °C). In the remaining areas tested on the wall cross-section at +20 °C, the impact energy exceeded the minimum required value of 27 J in the Charpy test. The tests revealed the presence of a network of cracks in areas adjacent to the inner surface of the ladle wall, which had a negative impact on the impact energy values, as did the presence of non-metallic inclusions. The changes found in the microstructure as a result of the ladle operation caused significant differences in properties such as impact energy and hardness, while also affecting, though to a lesser extent, the mechanical properties (UTS = 397–434 MPa; YS = 222–236 MPa). Full article

The material properties of P91 steel, a critical high-temperature heat-resistant steel, are critically dependent on the uniformity of its macro-composition distribution. This paper presents the first application of Spark Mapping Analysis for Large Samples (SMALS) for the non-destructive, full-field characterization of macro-composition distribution in P91 steel ingots and finished tubes. To address the analytical challenges posed by large-sized specimens, an innovative partition-based statistical analysis model was developed, enabling the effective demarcation of large-scale macro-segregation areas. Utilizing Sample A as the paradigm, a systematic methodology and workflow for the partition analysis were established, successfully identifying and quantifying the widths of its positive and negative segregation bands (namely 6 mm, 20 mm, and 8 mm). This approach was subsequently applied to samples from different smelting batches (B1, B2, C1, C2), effectively delineating macro-segregation areas within each sample and performing quantitative evaluations based on the statistical upper segregation limit. The findings provide essential experimental insights into the full-field compositional heterogeneity of P91 steel and deliver critical methodological guidelines for optimizing steel smelting processes to control and mitigate macro-segregation. Full article

Final electromagnetic stirring (F-EMS) effectively improves macrosegregation and central porosity in round bloom continuous casting, while the flow and solidification of molten steel under F-EMS have a direct impact on metallurgical properties. Fluid flow and solidification behavior in a 600 mm round bloom continuous casting process with F-EMS were simulated. The influence of the liquid fraction model on strand temperature distribution was investigated. The flow of molten steel was analyzed under both continuous and alternate stirring modes. The results indicated that in continuous stirring mode, the stirring velocity fluctuates between peaks and troughs over a specific period. The closer the F-EMS is to the meniscus, the larger the mushy zone area and the higher the stirring velocity. Due to the 10+ s rise time for current intensity, a 25 s forward and reverse stirring duration is recommended for Φ600 mm round bloom continuous casting with F-EMS. Full article

In this study, 8Cr4Mo4V steel was selected as the research material to develop a numerical model of the macrosegregation phenomenon during vacuum arc remelting (VAR). The accuracy of the model was validated by comparing it with the literature and experimental results. According to the simulation results, molten steel flows down along the solidification front, resulting in positive segregation at the center and negative segregation close to the edge of the ingot. Solute enrichment reduces the undercooling of the alloy system, which in turn decreases the local solidification rate and causes a slight increase in steady-state molten pool depth. Notably, as the molten pool depth increases, the temperature gradient decreases, while the local cooling rate remains nearly constant, which leads to an increase in the local solidification rate again. Consequently, the positive segregation degree at the ingot’s center is gradually alleviated, and the depth of the molten pool gradually decreases. Furthermore, macrosegregation in VAR ingots becomes pronounced with an increase in melt rate. The main reason for this is due to the increased molten pool depth when the melt rate is increasing, which strengthens fluid flow and accelerates the migration of solute elements to the center. Additionally, due to the increase in the extent of solute enrichment when the melt rate is increasing, the degree of fluctuation in both the steady-state molten pool depth and positive segregation increases. Full article

This study examines the Inconel 718/Ti6Al4V multi-material with a Cu and Nb interlayer produced by SLM. To achieve this, it is necessary to investigate the microstructure, the chemical and phase composition, and the hardness of the interfacial zone in the multi-material samples. Furthermore, it is necessary to determine the impact of interlayer utilization on the mechanical properties of multi-material samples. The investigation showed that the formation of island macro-segregation was observed in all interfacial zones of the multi-material samples. The interfacial zones, Ti6Al4V/Nb and Cu/Inconel 718, exhibited a relatively sharp transition in the chemical composition. In contrast, the Cu/Nb interfacial zone exhibited a gradual transition. The results of the chemical composition study indicated that the width of the Nb/Cu transition zone was approximately 700 μm. No new phases were identified in the production of the multi-material samples. The typical phases were present in the alloy zone, as well as in the Nb/Cu interfacial zone. During the transition from the Ti6Al4V zone to the Inconel 718 zone through the Nb and Cu zones, the average microhardness values changed as follows: 270 → 190 → 120 → 300 HV. The ultimate tensile strength values for the multi-material samples reached 910 MPa. Full article

Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high-pressure die casting (HPDC) process for alloys between liquid and solid temperature regions is still not fully understood. To investigate the influence of fluid flow and the size of externally solidified crystals (ESCs) on the evolution of dilatant shear bands in HPDC, various filling velocities were trialled to produce HPDC samples of Al8SiMnMg alloys. This study demonstrates that crystal fragmentation is accompanied by a decrease in dilatational concentration, producing an indistinct shear band. Once crystal fragmentation stagnates, the enhanced deformation rate associated with a further increase in filling velocity (from 2.2 ms⁻¹ to 4.6 ms⁻¹) localizes dilatancy into a highly concentrated shear band. The optimal piston velocity is 3.6 ms⁻¹, under which the average ESC size reaches the minimum, and the average yield stress and overall product of strength and elongation reach the maximum values of 144.6 MPa and 3.664 GPa%, respectively. By adopting the concept of force chain buckling in granular media, the evolution of dilatant shear bands in equiaxed solidifying alloys can be adequately explained based on further verification with DEM-type modeling in OpenFOAM. Three mechanisms for ESC-enhanced dilation are presented, elucidating previous reports relating the presence of ESCs to the subsequent shear band characteristics. By applying the physics of granular materials to equiaxed solidifying alloys, unique opportunities are presented for process optimization and microstructural modeling in HPDC. Full article

The process of symmetrical multidirectional pressure was adopted to inhibit the macrosegregation of eutectic Si in squeeze cast A356 alloy. Five pressure modes were applied to study the effects of multidirectional pressure and the timing of pressure application on the macrosegregation of eutectic Si. The results show that the directional movement of the solute-rich liquid phase could be inhibited by symmetrical multidirectional pressure. Therefore, the macrosegregation of eutectic Si in the casting part was inhibited. Moreover, the timing of pressure application should be matched with the local pressure position. After the effective inhibition of the macrosegregation of eutectic Si, the elongation of the alloy was significantly improved, reaching up to 7.12%. In addition, the plastic deformation region was observed at the local pressure position. The grains in the plastic deformation region were refined. The proportion of low-angle grain boundaries in the deformed region was about 30%, which was much higher than that in the other undeformed region. The size of the Fe-containing intermetallics in the deformed region decreased to 5–10 μm, which is favorable for the mechanical properties of the alloy. Full article

In this work, a novel internal heat absorption technology using inorganic material rods is employed during the solidification process of steel ingots, aiming to control their solidification and improve the quality of the final product. The study investigates the effect of the insertion depth of inorganic materials on the solidification microstructure and macrosegregation of 2.5-ton 42CrMo ingots. The mechanical properties of samples from the product are also tested. A numerical simulation model for casting 2.5-ton ingots is established and implemented in Ansys Fluent fluid simulation software, with inorganic material rods set at different preset depths. The simulation explores the physical processes of the melting and floating of inorganic materials in molten steel, as well as their effects on the temperature and flow fields of the material. The results show that deeper insertion of inorganic materials (200 mm from the hot top) reduces the tendency for macrosegregation compared to that at the insertion depth of 100 mm. Specifically, the positive segregation area decreases by 10.35%, while the negative segregation area decreases by 15.32%. Moreover, deeper insertion results in a significant refinement of the solidification microstructure, ultimately enhancing the mechanical properties of the products machined from the ingots (i.e., the yield strength increased by 4.7%). The numerical simulation results indicate that as the placement depth of inorganic materials in the ingot mold increases, the cooling effect becomes more significant, the flow area of molten steel initiated by the inorganic materials expands, and the linear velocity of the double-circle flow increases. This further explains why the solidification quality of the ingots improves with the increasing placement depth of inorganic materials. Full article