The rising demand for high-quality steel in construction, automotive, and other industrial sectors presents significant challenges, particularly regarding energy consumption and CO₂ emissions from large-scale production. This study explores the use of rapid tempering as a heat treatment strategy to enhance the mechanical properties of low carbon steel while potentially reducing the environmental footprint of steel manufacturing. Rapid tempering was performed following rapid austenitization at 1000°C for 90 seconds using a 7-kW induction furnace, followed by quenching in ice water. Soaking times of 5, 15, and 20 seconds were applied during tempering, and results were compared with conventional heat treatment. The rapid tempering process resulted in a microstructure consisting of tempered martensite, with only slight morphological changes in the martensitic phase compared to conventional tempering, and the formation of markedly finer cementite precipitates. Mechanical testing demonstrated superior performance in rapid tempering, with the 5-second condition achieving the highest hardness (422.667 HV), tensile strength (1308.9 MPa), and yield strength (1270 MPa), while the 20- second condition yielded the highest toughness (139.336 J/cm²) and elongation (33.833%). Based on the balance among tensile strength, hardness, and toughness, the RA-RT 5- second specimen exhibited the most optimal mechanical performance.
This study investigates the structure, mechanical properties, and corrosion resistance of low-nickel nitrogen-alloyed austenitic stainless steels (Cr17Mn9Ni3N, 05Cr18Mn10Ni3N) as cost-effective alternatives to conventional AISI 304L and AISI 321 grades. The alloys were produced by vacuum induction melting with nitrogen introduced via nitrided ferrochrome. Microstructural analysis confirmed fully austenitic structures with finer grain sizes (ASTM No. 4.5–6.0) compared to conventional steels (ASTM No. 3.5–4.0). Mechanical testing revealed superior yield strength (~414 MPa) and tensile strength (~730–748 MPa) in nitrogen-alloyed steels, attributed to solid-solution strengthening by nitrogen. However, the impact toughness at cryogenic temperatures (-196°C) was reduced, and brittle facets were found on the fracture surface. Potentiodynamic polarization tests showed that AISI 304L steel exhibited a higher pitting potential. The pitting potentials of Cr17Mn9Ni3N and 05Cr18Mn10Ni3N steels were lower than that of AISI 304L but higher than that of AISI 321 steel. Economic analysis highlighted significant cost savings potential through nickel substitution with nitrogen. The results validate nitrogen-alloyed steels as viable alternatives for applications requiring high strength and corrosion resistance, though cryogenic applications require careful nickel content optimization.
There has been a focus on environmental protection and the recycling of solid waste resources, particularly fly ash and aluminum dross. Efforts to utilize fly ash efficiently have increased. In this paper, a process is introduced for producing alumina-rich slag and ferrosilicon alloy through aluminothermic reduction of fly ash with aluminium dross. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirm the formation of spherical ferrosilicon alloy encased in a loose, porous alumina matrix during the aluminothermic reduction process. Thermodynamic calculations indicated that the reduction temperature of $ \mathrm{SiO_2} $ and mullite decreases in the presence of $ \mathrm{Fe_2}\mathrm{O_3} $. Under conditions of 1673 K, a specific aluminium dross to fly ash ratio (A/F), and a reduction time of 20 minutes, the magnetic fraction contains 85.89% ferrosilicon, while the non-magnetic fraction has an alumina content of 79.42%. This process offers a solution with potential environmental and economic benefits for the application of fly ash and aluminum ash.
The phase equilibria of the ternary Al-Cr-La system were investigated in the Al-rich corner at 600° C, with a minimum Al content of 98.77 at.%. The formed phases, transformation temperatures (specifically liquidus and solidus), and microstructure evolution were experimentally determined by isothermal annealing at 600° C for 600 hours and by Differential Scanning Calorimetry (DSC) analysis. A Scanning Electron Microscope (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDXS) was used to fully characterize the samples. The equilibrium microstructure consists of (Al), the binary phase $ \mathrm{Al_{45}} \mathrm{Cr_7} $, and the ternary phase $ \mathrm{LaCr_2} \mathrm{Al_{20}} $ in samples with increased Cr content (from 0.03 up to 1.12 at.%), while it consists of (Al), the mixture (Al) + $ \mathrm{Al_{11}} \mathrm{La_3} $, and the ternary $ \mathrm{LaCR_2} \mathrm{Al_{20}} $, phase in samples with increased La content (from 0.03 up to 0.45 at.%). It was observed that even a small amount of alloying elements leads to the formation of the ternary phase.
To efficiently recover valuable elements (Zn, K, Na) from blast furnace dust (BFD) and address issues such as alkali metal enrichment and disrupted furnace operation caused by its direct reuse, ammonia leaching experiments were conducted in this study using an $ \mathrm{NH_3} $·$ \mathrm{H_2O} $– $ \mathrm{NH_4}\mathrm{HCO_3} $ system combined with ultrasound and ammonium persulfate. Single-factor experiments were performed to investigate the effects of variables such as $ [ \mathrm{NH_3}]_T $ and solid-to-liquid ratio on the leaching efficiencies of Zn, K, and Na under ultrasonic conditions. Under the conditions of $ [ \mathrm{NH_3}]_T $ = 6 mol·$ L^{-1} $ , a solid-to-liquid ratio of 1:6, [$ \mathrm{NH_3} $]/[$ NH_4^+ $] = 1:1, 40°C, and 90 W ultrasound power, the leaching efficiencies of Zn, K, and Na reached 90.73%, 91.45%, and 91.56%, respectively. Based on these results, the effect of ultrasound combined with 1 mol·$ L^{-1} $ ammonium persulfate on zinc leaching was further evaluated, and the Zn leaching efficiency increased to 95.16%, while the leaching efficiencies of K and Na slightly increased to 92.35% and 92.50%, respectively. The enhanced Zn leaching is reasonably attributed to the synergistic effects of ultrasonic intensification and persulfate oxidation, in which ultrasound promotes particle fragmentation and mass transfer, while activated ammonium persulfate generates $ SO_4^{.-} $ radicals that facilitate the oxidation of refractory ZnS. Kinetic analysis indicated that Zn leaching was mainly controlled by the surface chemical reaction, and ultrasound reduced the apparent activation energy from 62.37 to 44.15 kJ·$ mol^{-1} $. This synergistic leaching process, with high selectivity and low cost, provides theoretical and technical references for BFD resource recovery.
Aluminum alloying is commonly used to improve high-temperature oxidation resistance. In this study, Al was incorporated into nanocrystalline coatings produced by magnetron sputtering of 310S chromium–nickel steel. The effect of this addition on the phase composition and morphology of the coatings, which influence the formation of protective oxide layers under high-temperature conditions, was investigated. The coatings were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), with emphasis on surface roughness, as well as X-ray diffractometry (XRD) to determine crystallite size and phase composition. The results showed that the addition of aluminum affects phase stability in the coatings. At Al contents of 1–2 at.%, there is a twofold reduction in the fraction of the fcc phase in the coating (and its disappearance at 5 at.%), along with a similar decrease in surface roughness. At the same time, crystallite size increases while the nanocrystalline structure is retained, creating favorable conditions for the formation of dense Al₂O₃ oxide layers on the coatings.
This study examines the spatial variability of HV5 hardness in industrially produced Direct Chill (DC) cast EN AW-5083 aluminium alloy ingots in the as-cast and homogenized conditions. Hardness measurements were performed at predefined sampling positions in the front and rear sections of six ingots using a Latin square design and evaluated by analysis of variance (ANOVA), coefficients of variation, correlation analysis, and linear regression. The results indicate a uniform longitudinal hardness distribution, with similar mean HV5 values at the front and rear sections, while significantly larger variations occur across the ingot cross-section. Slice height (i) and slice width (j) were identified as the dominant sources of variability. Homogenization reduced the overall mean HV5 from 81.8 HV5 to 75.7 HV5, decreased the coefficient of variation from 5.56% to 4.64%, and increased the correlation coefficient from r = 0.76 to r = 0.85. A statistically significant but limited relationship between the number of grains per unit area (NA) and hardness was observed, indicating that NA contributes to local hardness variations but is not the dominant factor controlling the overall spatial hardness distribution. The results indicate that homogenization does not increase hardness but improves its spatial homogeneity primarily through reduction of local microstructural and compositional heterogeneity.
This work investigates the application of the pack-boronizing process to a low-alloy steel of type ASTM A29 within the temperature range 1123-1273 K. Microscopic observations revealed the formation of a single Fe2B layer at all processing temperatures, with a less pronounced toothed interfacial morphology. The tribological behaviour of the boride layers was studied using pin-on-disc tests, and their nanomechanical properties, such as elastic modulus and nanohardness, were evaluated by nanoindentation tests. Furthermore, the Taylor expansion (TE) model was implemented to assess boron diffusivities in Fe2B, from which the activation energy was determined. The empirical verification of this approach has been made employing four additional boriding conditions.
A very popular material used for parts and components of machines operating under abrasive wear is cast alloyed steel with medium and high carbon content, which ensures sufficient hardness, and with the addition of elements such as Cr, Mn, Si, Ni, Mo. To improve the abrasive wear resistance of the tested alloys, carbide-forming elements such as vanadium were introduced in the amount of about 18 wt.% during melting. One melt, in which the total carbon content ranged from 3.4 to 3.9 wt.%, additionally contained 4.5 wt.% W. The measured hardness of the tested samples in the alloy with a carbon content of 3.4 wt% and the addition of 17.7 wt% V and 4.5 wt% W, the as-cast was approximately 535 HV and increased to approximately 665 HV after quenching. The highest hardness was obtained for an alloy containing 3.9 wt% C and 17.9 wt% V. In the as-cast state, the hardness of this alloy was 850 HV and increased to 950 HV after quenching from a temperature of 880°C and cooling in a 15% of Polihartenol HI polymer solution. The microstructure of test castings was composed of a martensitic matrix with low amounts of retained austenite characterized by the presence of lamellar carbides with a spherical cross-section, evenly distributed in the alloy matrix. In the majority of cases, those were M2C carbides, though in alloys with vanadium and tungsten, complex carbides of the (V,W)xCy type were also observed to occur. The highest resistance to abrasive wear of approximately 950 HV was obtained in a martensitic alloy with 17.9 wt% V+0.1 wt% W, quenched from a temperature of 880°C and cooled in a 15% of Polihartenol HI polymer solution. Its weight loss was two times lower than the weight loss of the reference cast GX70CrMnSiNiMo2 steel.
The hardness and strength of many alloys often differ when measured at the nano, micro, and macroscopic scales. Therefore, it is essential to study the mechanical behavior of important alloys across a wide range of length scales. In this work, we present a scenario in which two industrially significant alloys, In-718 and ASTM F75, exhibit different behaviors at the micro and macroscopic levels. Both alloys are promising candidates for similar applications in the aerospace and petroleum industries. The alloys were first 3D printed using selective laser melting (SLM) and then heat-treated in a vacuum. The average yield strength and percentage elongation (along the build direction) of the In-718 alloy were 29% and 19% higher, respectively, than those observed for the ASTM F75 alloy. The difference between the ultimate tensile strength (UTS) and Vickers hardness (at a load of 98 N) was almost negligible, i.e., less than 5%. In contrast to the Vickers hardness values of 3.9 GPa and 3.8 GPa, the average nanohardness of the In-718 and ASTM F75 alloys was 5.7 GPa and 7.6 GPa, respectively, which was substantially higher than their Vickers hardness. Furthermore, the ASTM F75 alloy demonstrated much better wear resistance in ScanningWear tests performed using a nanoindenter. The explanation for these differences and the similarities between macro- and nanomechanical behavior are presented in this work.
In this study, CP-Ti was prepared using the selective laser melting (SLM) technique to systematically investigate the effect of scanning speed on microstructure, mechanical properties, wear properties, and corrosion behavior. The optimum relative density of 99.87±0.12% was achieved at a scanning speed of 800 mm/s, with corresponding tensile strength, yield strength, elongation, and hardness values of 543±17 MPa, 453±7 MPa, 14±1%, and 294±4 HV, respectively. Additionally, SLMprocessed CP-Ti with optimum relative density exhibited the lowest wear rate (2.72×10-7 mm2/N) and excellent corrosion resistance. These results indicate that CP-Ti with high relative density, strength, and hardness, low wear rate, and excellent corrosion resistance can be fabricated by controlling the scanning speed, making it well-suited for biomedical implant applications.
The paper presents the results of investigations concerning the influence of growth velocity (v) and temperature gradient (G) on the interlamellar spacing (λ) in an irregular iron-carbon (Fe-C) eutectic unidirectionally crystallized. The aim of this study was to verify the growth model of D.J. Fisher and W. Kurz and to determine the relationship λ = f(v, G) based on experimental and numerical analysis. The crystallization process was carried out using the Bridgman-Stockbarger method with liquid metal cooling (LMC), and the structure was studied using optical microscopy and scanning electron microscopy. In parallel, numerical simulations were performed in ProCAST to determine the temperature gradient in the liquid at the crystallization front. The results showed that increasing the growth velocity at constant G leads to a decrease in interlamellar spacing λ, while at constant velocity a decrease in G results in an increase in λ. The experimental data obtained showed good agreement with the results of mathematical modelling, confirming the suitability of the W. Kurz and D.J. Fisher model in describing the crystallization of irregular Fe-C eutectic alloys.
The traditional magnesium reduction process consumes a significant amount of energy, which contradicts China’s green and low-carbon development goals. Therefore, exploring more energy-efficient methods is crucial for environmental protection. The magnesium reduction rate is influenced by several factors, including gas flow rate, briquetting pressure, ferrosilicon content, reduction temperature, and reduction time. In this study, data analysis utilizing a machine learning algorithm: support vector machine (SVM)—was employed to predict the magnesium reduction rate. Given that energysaving processes are a primary objective for enterprises, the processing was optimized using the particle swarm optimization (PSO) algorithm based on the SVM model, while maintaining a constant magnesium reduction rate. This optimization aims to reduce energy and gas consumption during the magnesium smelting process. Experimental verification of the magnesium reduction rate under the optimized processing conditions demonstrated that the application of machine learning algorithms can lead to resource savings in the magnesium reduction process. To further evaluate the environmental benefits of the optimized process, a Life Cycle Assessment (LCA) focusing on energy consumption and carbon dioxide ( \mathrm{CO_2} ) emissions was conducted. The LCA results indicate that the optimized process significantly reduces life cycle energy consumption (reduced by 5.33%) and \mathrm{CO_2} emissions (reduced by 3.63%) compared with the initial process, providing precise environmental performance data for the promotion and application of magnesium alloys in lightweight structures.
The molten chromite reduction direct alloying process serves as a pivotal metallurgical technology in stainless steel production, offering advantages such as reduced carbon consumption and improved production efficiency. In this study, to reveal the dissolution mechanism of chromite, pure phase of synthetic FeCr₂O₄, the main component of chromite, was used to replace chromite with complex compositions. The dissolution kinetics of FeCr₂O₄ in MgO-$ \mathrm{Al_2} $$ \mathrm{O_3} $ -Si$ \mathrm {O_2} $ slag were systematically investigated as functions of stirring intensity, MgO/SiO2, and temperature, revealing its non-isothermal reactive dissolution characteristics. Experimental results demonstrated that the solubility of $ \mathrm{Cr_2} $$ \mathrm{O_3} $ exhibited a trend of initial increase followed by subsequent decrease as the MgO/Si$ \mathrm{O_2} $ mass ratio increased. The maximum solubility was observed at a MgO/Si$ \mathrm{O_2} $ mass ratio of 0.56. Additionally, temperature-related studies indicated that the dissolution of FeCr₂O₄ is progressively enhanced with increasing temperature under elevated thermal conditions (1500-1600℃). Meanwhile, scanning electron microscopy (SEM) analyses confirmed that the interfacial reaction between FeCr₂O₄. and slag components generated Mg$ \mathrm{Al_2} $$ \mathrm{O_4} $, Mg $ \mathrm{Cr_2} $$ \mathrm{O_4} $ and MgO-xFeO solid solution, forming a boundary layer on the surface of unreacted FeCr₂O₄.The dissolution reaction on the surface of FeCr₂O₄ was the rate-controlling step in the dissolution process. The calculated activation energy of the dissolution process was 65.43 kJ· $ mol^{-1} $.
Computational thermodynamics provides essential information for materials design. The CALPHAD (CALculation of PHAse Diagrams) method based on thermodynamic databases can be used for thermodynamic optimization and for calculating phase diagrams and thermodynamic properties in multicomponent systems. This article reviews the algorithms implemented in software for optimizing thermodynamic parameters. These software tools offer strong support for developing accurate thermodynamic databases. Recent advances in algorithms for thermodynamic parameter optimization are summarized, and their respective characteristics and potential limitations are analyzed. Finally, the development trends of software and algorithms for thermodynamic parameter optimization are discussed. This review will help interested readers understand the principles of thermodynamic optimization and contribute to the advancement of related algorithms.
This research investigated the influence of varying copper (Cu) concentrations (0, 5, 7, and 9 wt.%) on the sintering behaviour, microstructural development, and mechanical characteristics of Ti-18Nb alloy, fabricated through conventional powder metallurgy. Under specific sintering conditions (1150 degrees C for 5 hours), Cu addition led to a more homogeneous microstructure and promoted the complete dissolution of Nb particles. X-ray diffraction (XRD) analysis confirmed the presence of alpha (alpha) and beta (beta) Ti phases, along with the Ti2Cu phase, with its peak intensity increasing as Cu content rose. Mechanical properties were significantly enhanced by Cu addition. Yield strength increased almost linearly with Cu content. Compressive strength notably increased with 7 wt.% Cu, reaching 980 MPa, and slightly exceeded this value with 9 wt.% Cu. Hardness values increased due to solid solution strengthening in the alpha-Ti phase and the precipitation of the Ti2Cu phase, with the highest hardness (222 HV) observed in the 7 wt.% Cu alloy. The elastic modulus initially increased with 5 wt.% Cu, then subsequently decreased with further Cu additions; the Ti-18Nb-7Cu alloy exhibited the lowest elastic modulus at 13.34 GPa. Furthermore, the resilience of the alloys improved with the formation of the Ti2Cu phase, and a maximum value of 13.15 MJ m-3 was achieved.
This study investigates microstructure development of AA5182 Al-Mg alloy under various homogenization conditions and how these conditions affect recrystallization processes and texture development during the laboratory hot-rolling. Homogenization treatments were conducted for 16 h at 490 degrees C and for 4 h, 16 h and 96 h at 550 degrees C. Scanning electron microscopy (SEM) characterization including energy-dispersive X-ray spectroscopy (EDX) revealed the presence of Al3(Fe,Mn) and Alm(Fe,Mn) phases as Fe/Mn-bearing microconstituents in the as-cast state. These transformed into Al6(Fe,Mn) and alpha-Al(Fe,Mn)Si during homogenization treatments. The treatments also led to precipitation of Al6(Mn,Fe) and alpha-Al(Fe,Mn)Si dispersoid particles. The results of electron backscattered diffraction (EBSD) indicated that a weak deformation texture was present after hot-rolling. The morphology of grains and the degree of restoration were significantly influenced by homogenization conditions. The distribution and density of dispersoids had a strong effect on the mechanisms of recovery and recrystallization.
In this study, FeNiCu alloys with two different copper contents were produced by arc melting. The aim was to investigate the effects of Cu content on the microstructural, mechanical, thermal, and M & ouml;ssbauer properties of the alloys. Microstructures were examined using SEM micrographs. Vickers hardness tests were conducted to evaluate mechanical strength. Thermal behavior was analyzed using DSC. Magnetic characteristics were studied by M & ouml;ssbauer spectroscopy. SEM analysis showed the presence of martensitic structures in both alloys, with the alloy containing more Cu exhibiting a higher amount of martensite. Hardness increased from 169.1 HV to 190.2 HV as Cu content increased. DSC results confirmed the martensitic transformation. The alloy with higher Cu content showed a higher transformation temperature and greater transformation energy released. M & ouml;ssbauer spectra indicated the presence of both magnetically ordered and non-ordered phases in both alloys. Hyperfine parameters demonstrated changes in the local atomic environment due to Cu addition. The weak singlet obtained was associated with the FCC phase. The two sextets were attributed to ferromagnetic BCC phases arising from different environments of the Fe atom. The other sextet, with a low internal magnetic field of around 18 T, was ascribed to possible Ni- and/or Cu-rich surroundings of the Fe atom. Overall, increasing Cu in the alloy altered the microstructure, improved hardness, shifted the martensitic transformation temperature, and modified the magnetic hyperfine interactions. These results may aid in designing advanced Fe-based materials for structural and magnetic applications.
This study systematically examines the influence of precipitation on the microstructural and mechanical properties of Inconel 718 superalloy in as-received, solution heat-treated, peak-aged, and overaged conditions. Cold, warm, and hot deformation tests were performed at 25 degrees C, 400 degrees C and 800 degrees C using a constant strain rate of 5.55x10-4 s-1. The results indicated dynamic strain aging during warm deformation at 400 degrees C in all investigated conditions. However, at temperatures above 400 degrees C, a pronounced reduction in strength was observed, accompanied by a corresponding increase in elongation for most conditions. Notably, the solution heat-treated samples exhibited anomalous behavior, showing an increase in Rp0.2 after deformation at 800 degrees C. This suggests the occurrence of dynamic precipitation during hot deformation in the solution heat-treated samples.
This study investigates the effects of Gas Metal Arc Welding (GMAW) parameters-specifically welding speed and stickout-on the dilution and mechanical properties of welded joints composed of ultra-high hardness quenched and tempered (UHH-Q&T) armor steel and austenitic stainless steel filler metal. An optimization methodology was used to set constant parameters, including wire diameter, gas flow rate, welding voltage, and wire feed speed, based on equipment capabilities. Experimental trials varied welding speed and electrode stick-out while maintaining a constant current through inductance control. Although the welding parameters affected the melted base and filler metal areas, the dilution percentage remained unaffected. The correlation between dilution and welding current was validated. Microstructural and mechanical analyses confirmed the consistent behavior of the welded joints under the tested conditions.
