Search Results (152)

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module and the CALPHAD TCOX11 database to develop LF refining schedules capable of upgrading conventional S355J2R steel to weathering steel grades: S355J2W and S355J2WP. First, the sensitivity of predicted compositions to key kinetic inputs was quantified. The validated model was then used to simulate deoxidation and desulfurization sequences, predicting the evolution of liquid–steel and slag compositions, slag basicity, and FeO activity throughout the LF cycle. Subsequently, Cr- and P-ferroalloys were introduced to design tap-to-tap schedules that meet the EN 10025-5 chemical specifications for S355J2W and S355J2WP. To correlate simulation outcomes with material performance, plates produced following the modeled schedules were evaluated through a 1000 h accelerated salt spray test. Steel density and steel phase mass transfer coefficients were found to produce the highest prediction sensitivity (up to 7.5 wt.% variation in C and S), whereas slag phase parameters exhibited a lower impact. The predicted steel compositions showed strong agreement with industrial values obtained during plant trials. SEM-EDS analyses confirmed the development of a Cr-enriched protective patina and validated model-based alloying strategies. Full article

The liquidus and solidus temperatures, the initial temperature of the solidification of binary eutectics, and the partition ratios of the solid solution at the Al corner of the ternary eutectic-type Al-Si-Cu alloy system were calculated using the thermodynamically based ESTPHAD method. It is shown that these data can be calculated from the liquidus and solidus data of the two binary equilibrium phase diagrams (first estimation), the binary phase diagram and the eutectic valleys in the ternary system (second estimation), as well as the binary phase diagram, the eutectic valleys, and one (third estimation) and more (fourth estimation) liquidus and solidus temperatures of the ternary equilibrium phase diagram with varying precisions. A database calculated with Thermo-Calc software (version 4.1.0.4995), was used for the calculations. Full article

Solidification cracking is a critical defect in Cu–steel dissimilar laser welding for cylindrical lithium-ion battery busbar assembly, yet the metallurgical role of phosphorus (P) in crack formation has not been quantitatively established. In this study, the influence of phosphorus in the coating layer on weld solidification behavior was clarified by preparing Cu substrates with four different coating conditions—Ni–P-coated Cu (10 and 50 μm) and pure Ni-coated Cu (10 and 50 μm)—and performing high-speed single-mode fiber-laser welding under identical heat-input conditions. Shear-tensile testing, EPMA-based microstructural analysis, and Thermo-Calc solidification calculations were combined to correlate P segregation with solidification cracking susceptibility. The Ni–P 10 μm coating generated severe solidification cracking compared with the pure Ni 50 μm coating, which was attributed to excessive P enrichment in the terminal liquid phase (up to 8.8 mass%). This enrichment significantly expanded the mushy-zone width to approximately 869 K, yielding a highly solidification crack-susceptible fusion zone. In contrast, 50 μm pure Ni coatings produced narrow mushy-zone widths (200–400 K) and extremely low residual P levels (~0.1 mass%), resulting in fully crack-free microstructures. The 50 μm Ni coating exhibited the highest shear-tensile strength and largest rupture displacement among all conditions, confirming that suppression of P segregation directly improves both structural integrity and mechanical performance. Overall, this study demonstrates that phosphorus enrichment critically governs the solidification-cracking susceptibility of Cu–steel dissimilar welds by widening the solidification temperature range. Eliminating P from the coating layer and applying an adequately thick pure Ni coating constitute highly effective strategies for achieving crack-free, mechanically robust welds in lithium-ion battery busbar manufacturing. Full article

Recently, we reported an antiferromagnetic ground state for equiatomic Al-Cr in the B2 structure. Here, by a joint theoretical–experimental study, we investigate the effect of Co additions to the Al-Cr alloy with the aim to synthesize a ferromagnetic B2 phase. Al₅₀Cr₃₈Co₁₂ (at.%) is prepared by arc melting from high-purity raw materials and solidifies into a combination of a Co-enriched B2 phase, a Co-depleted BCC phase, and an Al₈Cr₅ intermetallic phase. The as-cast alloy is ferromagnetic with a Curie point of 260 K, primarily due to the presence of about 54% B2 phase. Subsequent annealing decreases the fraction of the B2 phase to 27% with depletion of Cr from 20.2 at.% to 16.1 at.%, which leads to a reduction in its ferromagnetic behavior. Calculations based on Density Functional Theory (DFT) predict a corresponding decrease in the total magnetic moment and Curie temperature of the B2 phase by annealing. The present findings highlight the roles of Cr and Co in facilitating the formation of a metastable ferromagnetic B2 phase in this alloy. Full article

Cracks were found at the gate of the 430Cb ferritic stainless steel exhaust system jet base produced by investment casting. In this paper, the cracks of failed stainless steel castings were comprehensively analyzed by means of macroscopic inspection, laser confocal microscopy, field emission scanning electron microscopy, electron backscatter diffraction, X-ray diffractometer, ProCAST (version 2018, ESI Group, Paris, France) simulation and Thermo-Calc (TCFE10 database, 2022a, Thermo-Calc Software AB, Solna, Sweden) thermodynamic calculation. It can be concluded that all the cracks originate from the gate on the surface of the casting, and the fracture surface shows brittle intergranular characteristics, which can be determined as cold cracks. The formation of cold cracks can be attributed to the fact that the local stress generated during cooling after the casting solidifies exceeds the strength limit of the material itself. As the gate is the final solidification zone, shrinkage is limited and stress is concentrated. The grains are coarse, and the microstructure defects such as shrinkage porosity, pores and needle-like NbC further weaken the plasticity of the grain boundaries, promoting the crack to propagate along the direction of the maximum principal stress. The uneven cooling rate and shell constraint during the investment casting process make it difficult to release stress, and the existence of microstructure defects are the fundamental causes of crack generation. Full article

A comprehensive study of the structural–phase transformations and hydrogen desorption kinetics in the Mg₅₆Al₄₄ system was conducted using a multistage approach combining thermodynamic modeling CALPHAD, Thermo-Calc 2025a, mechanical synthesis (MS), spark plasma sintering (SPS), and subsequent dispersion treatment. Thermodynamic modeling revealed a stable existence region of the intermetallic compound Mg₁₇Al₁₂, exhibiting Cp-T anomalies at 303 and 351 °C that closely corresponded to the experimental DSC/TGA results. Microstructural analysis showed that varying the ball-to-powder ratio BPR 20:1 and BPR 30:1 determines the defect density, crystallite size 25–45 nm, and lattice strain 1.5–3.0 × 10⁻³, all of which directly influence the hydrogen desorption kinetics. For the samples synthesized at BPR 30:1, the onset temperature of hydrogen release decreased to 180–200 °C while maintaining a hydrogen storage capacity of 4.9 wt.%, accompanied by a reduction in the apparent activation energy of desorption from 92 to 74 kJ·mol⁻¹ according to the Kissinger method. The dispersion stage partially disrupted and redistributed the surface MgO layer, leading to a reduction in its overall contribution and improvement in structural homogeneity, rather than complete oxide removal. The combined MS-SPS-dispersion processing route enabled controlled nanostructure formation, reduced the hydrogen desorption temperature by approximately 100 °C compared to conventional MgH₂-based materials, and significantly enhanced the thermokinetic performance. These findings demonstrate that Mg-Al alloys are promising candidates for solid-state hydrogen storage systems with improved desorption kinetics and reduced activation barriers. Full article

The objective of this study was to develop novel alloys of the Ti-15Nb-xTa system (x = 0, 10, 20, and 30 wt.%) and to evaluate the effect of tantalum addition on the structure, microstructure, hardness, and elastic modulus for biomedical applications. The ingots were produced using an arc melting furnace under a controlled argon atmosphere. Chemical composition analyses were performed using energy-dispersive spectroscopy (EDS) to determine the alloying element fractions and to conduct chemical mapping. The Thermo-Calc software (https://thermocalc.com/, 4 September 2024) was employed to predict the influence of Ta on the phase transformation temperatures. Structural and microstructural characterizations were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns enabled the identification of the phases, the relative volume fractions, and the lattice parameters of the unit cells. As mechanical properties, Vickers microhardness and elastic modulus were measured. The results revealed that increasing Ta content decreased the β-transus temperature but increased the melting temperature of the alloys. Structural and microstructural characterizations indicated that the Ti-15Nb alloy consisted of α′ + α″ phases, Ti-15Nb-10Ta of α″ + β phases, Ti-15Nb-20Ta of α″ + β + ω phases, and Ti-15Nb-30Ta of metastable β phase. Hardness and elastic modulus results exhibited similar behavior: the alloy with the highest fraction of the α″ phase (Ti-15Nb-10Ta) displayed the lowest hardness and elastic modulus, whereas the alloy containing the ω phase (Ti-15Nb-20Ta) presented significantly higher values. Among the studied alloys, Ti-15Nb-10Ta stands out due to its low elastic modulus (57 GPa). In vitro cellular assays demonstrated that Ti-15Nb-Ta alloys promote osteoblast proliferation while exhibiting no cytotoxicity. Full article

This work studied microstructure evolution during the intercritical treatment of Fe–1.4Si–2.6Mn–0.17C TRIP steel. Steel specimens were heated in the intercritical region, α ferrite and γ austenite phases, at 750 °C for 30 min, water-quenched, air-cooled, and austempered at 350 °C for 30 min. Microstructural analysis was performed by optical microscopy, scanning electron microscopy, and X-ray diffraction. All heat-treated specimens were mechanically characterized by uniaxial tension and Vickers hardness tests. Thermo-Calc software 2024b was used to analyze the microstructure and phases of heat-treated steel. The microstructural characterization results revealed that the phases and microconstituents were ferrite, austenite, cementite, pearlite, and retained austenite. Thermo-Calc results were consistent with the phases and microconstituents identified for each heat-treatment condition. On the other hand, the tension test results showed that the yield strength and ultimate tensile strength ranged between 690 and 820 MPa and 1190–1255 MPa, respectively, for these heat-treated steels. Likewise, Thermo-Calc proved to be a powerful tool for designing intercritical heat treatments for TRIP steels. Full article

This study comprehensively evaluates the latent heat of hypoeutectic AlSi5Cu alloys with 1, 2, and 4% of Cu by mass, investigating their solidification behavior under controlled cooling conditions. Latent heat, a critical thermophysical property, significantly influences solidification and microstructural formation in casting processes. The evaluation employed an integrated approach, combining experimental measurements from Differential Scanning Calorimetry (DSC) and thermal analysis (TA-Newtonian method) with computational assessments performed using JMatPro and Thermo-Calc software packages. The findings reveal a reasonable agreement between the measured and calculated latent heat values, suggesting that methods beyond DSC, such as commercial software and thermal analysis techniques, offer acceptable and viable alternatives for determining latent heat in AlSiCu alloys. While DSC served as the experimental reference, providing particularly consistent lowest values for AlSi5Cu1 and AlSi5Cu2, relative error analysis indicated that JMatPro generally yielded results closest to DSC, especially for AlSi5Cu2 (0.245% relative error), and the TA-Newtonian method also showed strong agreement, particularly for AlSi5Cu1 (0.356% relative error) and AlSi5Cu4 (0.787% relative error). Maximum deviation was observed with Thermo-Calc for AlSi5Cu1 (7.474%). These discrepancies are primarily attributed to inherent differences in the underlying thermodynamic databases for computational tools and the sensitivity of experimental techniques to specific material properties and solidification behaviors. Full article

In this study, we utilized Thermo-Calc software (2023a) to optimize the heat treatment process of martensitic stainless steel 90Cr18MoV through phase diagram calculations. The microhardness of 90Cr18MoV was characterized using a nanoindentation instrument. The microstructural morphology of the samples was analyzed using scanning electron microscopy (SEM). The composition of the samples was characterized through scanning electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Additionally, laser confocal microscopy (FIB) and transmission electron microscopy (TEM) were employed to characterize the precipitate phase composition and size before and after heat treatment, while also observing the dislocation structure within the samples. The relationship between the quenching temperature and the percentage of residual austenite content in the material was established. The influence of the dislocation structure and precipitate size on the hardness of the samples was investigated. The research findings confirm that the observed secondary hardening phenomenon in tempered samples is attributed to the co-precipitation of two types of carbides, M₂₃C₆ and MC, within the matrix. The study investigated the effects of the tempering temperature and duration on the size of secondary precipitates, indicating that M₂₃C₆ and MC particles with sizes less than or equal to 20 nm contribute to enhancing the matrix, while particles larger than 30 nm lead to a reduction in hardness after tempering. Notably, during the tempering process, M₂₃C₆ precipitated from the matrix nucleates on MC. Full article

Ferritic lightweight steels are an emerging class of low-density steels (LDSs) with promising mechanical properties. The study aimed to develop two ferritic lightweight steels with different Mn concentrations. Al was incorporated to achieve the lightweighting effect due to its relatively low atomic mass of substitutional solutions. The C concentration was kept at a minimum level to avoid the precipitation of carbides and the Mn addition was intended to increase solid solution strengthening. Thermodynamic calculations (Thermo-Calc) were employed to design the composition, analyze the phase constituents, and predict the phase transformation behavior. Microstructural investigation and hardness tests were conducted to experimentally verify the calculations. Both produced alloys exhibited a fully ferritic microstructure. Compared to industrially produced DP980 steel, a density reduction of about 7.2% and 8.3% was attained for the Fe-0.04C-5.5Al-1.6Mn-0.075Nb and Fe-0.04C-5.6Al-5.5Mn-0.08Nb steels, respectively. The steel with the higher Mn content showed increased hardness attributed to its solution strengthening effect. An increase in the hardness values was also measured with the progress in hot-rolling thickness reductions for both alloys. The alloying elements influenced the microstructural characteristics, phase transformation behavior, density, and hardness of the newly designed lightweight steels. Full article

This study investigates the distribution characteristics of residual ferrite in 304L austenitic stainless steel continuous casting slab and the impact of heat treatment processes on its content. Through optical microscopy (OM), thermodynamic calculation software (Thermo–Calc) and heat treatment experiments, it is found that the residual ferrite content along the thickness direction at the width center of the slab exhibits an “M”-shaped distribution—lowest at the edges (approximately 3%) and highest near the center (approximately 13%). Within the triangular zone of the slab, the residual ferrite content varies between 1.8% and 12.2%, with its average along the thickness direction also showing an “M”-shaped distribution; along the width direction, the average residual ferrite content is lower at the edge positions, while within the internal triangular zone, it ranges between 8% and 10%. The ferrite morphology changes significantly across solidification zones: elongated in the surface fine-grain zone, lath-like and skeletal in the columnar grain zone and network-like in the central equiaxed grain zone. Thermodynamic calculations indicate that the solidification mode of the 304L continuous casting slab follows the FA mode. Heat treatment experiments conducted across the entire slab thickness demonstrate effective reduction in residual ferrite content; the optimal reduction is achieved at 1250 °C with a 48 min hold followed by air cooling while preserving the original “M”-shaped distribution characteristic after treatment. Increasing the heat treatment temperature, prolonging the holding time and reducing the cooling rate all contribute to reducing residual ferrite content. Full article

To address the central cracking problem in continuous casting slabs of 38CrMoAl steel, high-temperature tensile tests were performed using a Gleeble-3800 thermal simulator to characterize the hot ductility of the steel within the temperature range of 600–1200 °C. The phase transformation behavior was computationally analyzed via the Thermo-Calc software, while the microstructure, fracture morphology, and precipitate characteristics were systematically investigated using a metallographic microscope (MM), a field-emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). Additionally, the effects of different holding times and cooling rates on the microstructure and precipitates of 38CrMoAl steel were also studied. The results show that the third brittle temperature region of 38CrMoAl steel is 645–1009 °C, and the fracture mechanisms can be classified into three types: (I) in the α single-phase region, the thickness of intergranular proeutectoid ferrite increases with rising temperature, leading to reduced hot ductility; (II) in the γ single-phase region, the average size of precipitates increases while the number density decreases with increasing temperature, thereby improving hot ductility; and (III) in the α + γ two-phase region, the precipitation of proeutectoid ferrite promotes crack propagation and the dense distribution of precipitates at grain boundaries causes stress concentration, further deteriorating hot ductility. Heat treatment experiments indicate that the microstructures of the specimen transformed under water cooling, air cooling, and furnace cooling conditions as follows: martensite + proeutectoid ferrite → bainite + ferrite → ferrite. The average size of precipitates first decreased, then increased, and finally decreased again with increasing holding time, while the number density exhibited the opposite trend. Therefore, when the holding time was the same, reducing the cooling rate could increase the average size of the precipitates and decrease their number density, thereby improving the hot ductility of 38CrMoAl steel. Full article

Sanicro 25 (X7NiCrWCuCoNb25-23-3-3-2) steel is specifically designed for use in superheater components within the latest generation of conventional power plants. These power plants operate under conditions often referred to as super-ultra-supercritical, with steam parameters that can reach up to 30 MPa and temperatures of 653 °C for fresh steam and 672 °C for reheated steam. While last-generation supercritical power plants still rely on fossil fuels, they represent a significant step forward in more sustainable energy production. The most sophisticated facilities of this kind can achieve thermodynamic efficiencies exceeding 47%. This study aimed to conduct a detailed analysis of the initial precipitation processes occurring in Sanicro 25 steel within the temperature range of 700–900 °C. The temperature of 700 °C corresponds to the operational conditions of this material, particularly in secondary steam superheaters in thermal power plants that operate under ultra-supercritical parameters. Understanding precipitation processes is crucial for optimizing mechanical performance, particularly in terms of long-term strength and creep resistance. To accurately assess the microstructural changes that occur during the early stages of service, a digital twin approach was employed, which included CALPHAD simulations and experimental heat treatments. Experimental annealing tests were conducted in air within the temperature range of 700–900 °C. Precipitation behavior was simulated using the Thermo-Calc 2025a with Dictra software package. The results from Prisma simulations correlated well with the experimental data related to the kinetics of phase transformations; however, it was noted that the predicted sizes of the precipitates were generally smaller than those observed in experiments. Additionally, computational limitations were encountered during some simulations due to the complexity arising from the numerous alloying elements present in Sanicro 25 steel. The microstructural evolution was investigated using various methods, including light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Full article

The phase transformations of Crucible Particle Metallurgy (CPM) American Iron and Steel Institute (AISI) M4 steel were studied during heat treatments using a CALPHAD-based method. The calculated results were compared with experimental observations. The optimum austenitizing temperature was determined to be about 1120 °C using Thermo-Calc software (2024b). Air-cooling and quenching treatments led to the formation of martensite with a hardness of 63–65 Rockwell C (HRC). The annealing treatment promoted the formation of the equilibrium ferrite and carbide phases and resulted in a hardness of 24 HRC. These findings with regard to phases and microconstituents are in agreement with the predictions derived from a Thermo-Calc-calculated time–temperature–transformation diagram at 1120 °C. Additionally, the primary carbides, MC and M₆C, which formed prior to the heat treatment and had a minor influence on the quenched hardness. In contrast, the tempering process primarily led to the formation of fine secondary M₆C carbides, which hardened the tempered martensite to 57 HRC. The present work demonstrates the application of a CALPHAD-based methodology to the design and microstructural analysis of tool steels. Full article