Search Results (417)

Against the background of blast furnace burden optimization and the low-carbon transition of the steel industry, the development of high-quality Mg-bearing fluxed pellets is of great significance for the efficient utilization of medium-high silica iron ore concentrates. In this study, Mg-bearing medium-high silica fluxed pellets with a fixed SiO₂ content of 5.5% were prepared, and the effect of basicity in the range of R = 1.0–1.4 on compressive strength, liquid phase behavior, slag phase composition, and pore structure evolution was systematically investigated. The results showed that the compressive strength of the pellets decreased from 2527 N/pellet to 2079 N/pellet as the basicity increased from 1.0 to 1.4. At 1250 °C, the liquid phase content first decreased from 2.66% to 1.30% and then increased to 7.38%, while the liquid phase viscosity decreased continuously. Meanwhile, the liquid phase composition evolved from a SiO₂-rich calcium–iron silicate system to a Fe₂O₃⁻ and CaO-rich system. XRD results indicated that Fe₂O₃ was the dominant crystalline phase in the pellets, accompanied by a small amount of Fe₃O₄, whereas no distinct highly crystalline slag phase was detected. The slag phase was mainly a Fe-Ca-Si composite slag, in which the Fe₂O₃ content increased and the SiO₂ content decreased with increasing basicity. At higher basicity, the number and size of pores increased, and the pore morphology evolved from dispersed fine pores to irregular large pores and locally connected pores. Meanwhile, the slag phase became more widely distributed and locally enriched, weakening the continuity of the iron oxide load-bearing skeleton, which was the main reason for the decrease in compressive strength. This study provides a theoretical basis for preparing high-quality Mg-bearing fluxed pellets from medium-high silica iron ore concentrates. Full article

This study investigates the thermochemical reaction behaviour of scheelite–millscale aluminothermy for direct tungsten alloying in steel production. Experimental mixtures of aluminium, millscale, and scheelite concentrate were simulated using gas–slag–metal (g-s-m) equilibrium calculations in FactSage 8.3 at 2200 °C, and compared with previously reported experimental results. The simulations reproduced metal yields accurately with 0.901 to 0.940 correlation coefficients and predicted tungsten levels consistent with measured steel compositions. However, significant discrepancies were observed in predicted silicon levels, with simulations overestimating steel %Si by up to 3.5%, despite negligible gas-phase losses. Oxygen partial pressure calculations indicate that the Fe/FeO reaction equilibrium controls process reduction conditions. Backcalculation of activity coefficients revealed that FactSage minimisation routines understated silicon activity coefficient values. SiO₂ mass transfer may play a role in low %Si in steel, but this is not clear due to differences in expected mass transfer regimes in aluminothermy under ASR and SHS conditions. Overall, the simulations demonstrate adequate predictive capability for alloying trends and metal yields while highlighting limitations in predicting silicon partitioning. These findings confirm the utility of thermochemical simulation for designing aluminothermic feed mixtures, reducing the number of experiments needed to optimise the aluminothermic feed mixture ratios. Full article

This study investigates the oxidation behavior and microstructural evolution of Sanicro 25 steel (X7NiCrWCuCoNb25-23-3-3-2) after long-term exposure to water vapor at 700 °C for 30,000 h. Particular attention was paid to the relationship between protective oxide-scale formation, chromium depletion in the near-surface region, and the possible changes in secondary-phase stability in the steel substrate. FIB-SEM tomography was applied to characterize the oxide scale and the underlying affected zone, enabling three-dimensional visualization of oxide morphology, interfacial voids, and microstructural reconstruction beneath the scale. Long-term exposure resulted in the formation of a continuous Cr-rich oxide scale with a thickness of approximately 2.6 µm and local Mn enrichment. The scale exhibited a complex multilayered morphology, consisting of outer Cr-rich oxide crystallites, fine-grained chromium oxides, and an inner heterogeneous Mn-enriched region, suggesting the possible formation of mixed spinel-type oxides. Si-enriched regions were observed near the oxide/metal interface; however, no continuous Si oxide layer was detected. Despite the presence of interfacial voids, no scale spallation was observed in the investigated regions. SEM-EDX analysis revealed a chromium-depleted subsurface zone extending to approximately 6.5 µm below the oxide scale. CALPHAD calculations suggest that local chromium depletion may reduce the thermodynamic stability of Cr-rich M₂₃C₆ carbides and the Nb–Cr–N-type Z phase. This possible reduction in phase stability may contribute to the formation of a precipitate-depleted region and local microstructural reconstruction beneath the oxide scale. In the bulk region, where oxidation effects were negligible, the microstructure consisted of an austenitic matrix containing M₂₃C₆ carbides, σ phase, Cr–Ni–Fe nitride with an A13-type structure, ε-Cu precipitates, Z phase, and W-rich Cu-containing TCP precipitates. The simulations further suggest that most secondary phases form during the early stage of annealing, whereas prolonged exposure is dominated by diffusion-controlled coarsening. Overall, Sanicro 25 shows good resistance to long-term steam oxidation at 700 °C due to the formation of a continuous Cr-rich protective scale. However, this protection is accompanied by chromium depletion and local near-surface microstructural changes, which should be considered when assessing the long-term stability and service performance of this steel under high-temperature steam conditions. Full article

Worn roller mill roll shafts made of Steel 45 require cost-effective surface restoration; plasma transferred arc (PTA) deposition of Ni–Cr–B–Si + WC composite coatings is a promising approach, yet the effect of arc current on coating quality remains insufficiently characterised for this substrate. Six coatings were deposited from PS-12NVK-01 powder (65 wt.% PG-10N-01 + 35 wt.% WC) at arc currents of 50–100 A on Steel 45 substrates using a ZTW3501DC PTA system; coatings were characterised by SEM, EDS mapping, XRD (HighScore Plus, PDF-2), Vickers microhardness profiling, and ball-on-flat tribological testing. EDS analysis revealed that compositional dilution increases from 18.1% at 60 A to 46.6% at 100 A; XRD identified WC + Cr₃C₂ + Ni₃B + Ni₂B + (Fe,Ni)γ at 50 A, transitioning through Cr₇C₃ + W₂C dominance at 80 A to an Fe₀.₆₄Ni₀.₃₆ matrix at 100 A; and coating thickness peaked at 2.70 mm at 80 A. The 60 A coating yielded the highest surface hardness (887 ± 76 HV, >4× the substrate), the lowest specific wear rate (4.00 × 10⁻⁶ mm³/(N·m), ~22× lower than uncoated Steel 45), and minimum dilution (18.1%), identifying 60 A as the most favourable deposition current for the restoration of roller mill roll shafts under the process parameters employed. Full article

This study investigates the growth and evolution of SiO₂-based inclusions in Si-killed steel under stagnant conditions and varying oxygen levels. Deoxidation experiments were conducted in a high-temperature furnace using commercial FeSi, with systematic variations in holding time and total oxygen content. Automated SEM–EDS analysis was employed to quantify inclusion size, number density, and chemical composition. Under stagnant conditions, SiO₂ inclusions were observed to grow and coarsen in the absence of melt agitation, following a t^1/3 scaling law. In high-oxygen melts, rapid inclusion growth was dominated by Stokes collision mechanisms, resulting in the formation of inclusions in the size range of 1–5 μm, which were subsequently removed by flotation. In contrast, low-oxygen melts exhibited slower growth kinetics governed primarily by Brownian motion and Ostwald ripening, producing smaller inclusions with characteristic sizes of 1–2 μm. These results demonstrate that the initial oxygen content plays a decisive role in controlling the dominant growth mechanisms and the extent of inclusion coarsening in non-agitated steel. Full article

The accumulation of residual elements such as Cu and Sn in recycled steels has become an increasingly critical issue, as their enrichment during high-temperature oxidation can lead to surface hot shortness and deterioration of surface quality. In this work, the coupled enrichment behavior of Cu and Sn at the oxide/steel interface and its regulation by Si were systematically investigated through high-temperature oxidation experiments and microstructural characterization. The results reveal that selective oxidation of Fe during high-temperature exposure leads to the rejection of Cu toward the oxide/steel interface, resulting in significant interfacial enrichment. The presence of Sn further intensifies this enrichment by lowering the melting point of the Cu-rich phase and promoting the formation of Cu–Sn liquid films along grain boundaries, thereby aggravating intergranular penetration and surface degradation. In contrast, the addition of Si effectively suppresses the interfacial enrichment of Cu and Sn. Microstructural analyses indicate that Si promotes internal oxidation and facilitates the formation of Si-containing oxides such as Fe₂SiO₄ within the oxide scale and near the interface, which modifies the interfacial structure and limits the diffusion and accumulation of Cu-rich phases. Consequently, the formation and penetration of Cu–Sn liquid are significantly inhibited. These findings clarify the coupling mechanism of Cu and Sn during oxidation and reveal an effective Si-based strategy for mitigating the detrimental enrichment of residual elements in recycled steels, providing guidance for improving the surface quality of steels produced from scrap-containing charges. Full article

Intragranular orientation gradients play a critical role in deformation and recrystallization texture evolution of silicon steel. In this study, the dependence of intragranular orientation gradients on grain orientation in a cold-rolled Fe-3%Si alloy was systematically investigated through electron backscatter diffraction (EBSD), complemented by a rate-dependent crystal plasticity model, incorporating grain boundary resistance. A comparative assessment of intragranular orientation gradients in the grain core and grain boundary regions revealed that they are markedly sensitive to grain orientation, with the grain boundary region exhibiting a higher orientation gradient than the grain core. The formation of intragranular orientation gradients is governed by the orientation stability during plastic deformation: stable convergent α (<110>//RD, rolling direction) and γ (<111>//ND, normal direction) orientations develop lower orientation gradients, whereas grains with unstable divergent λ (<001>//ND) orientations exhibit higher orientation gradients. Furthermore, intergranular interactions during rolling reduce orientation stability near grain boundaries, thereby promoting higher orientation gradients in the grain boundary region compared to the grain core. Full article

The corrosion behavior and time-dependent mechanism of 22MnB5 steel featuring a thinned Al-Si coating (60 g/m²) were systematically investigated in a chloride ion wet–dry cyclic environment, motivated by the demand for thinning and toughening development of aluminum-silicon coatings. A periodic immersion accelerated corrosion test using 3.5% NaCl solution was conducted, together with macro/microscopic morphology observation (SEM/EDS), phase analysis (XRD, FTIR), and electrochemical measurements (polarization curves, EIS). The Al-Si coated steel was studied over corrosion periods of 1, 8, 10, and 20 days to elucidate its corrosion behavior, interfacial evolution, and failure mechanism. The results indicated that the corrosion process exhibited a three-stage evolution: stable protection, rapid failure, and dynamic equilibrium. At the initial stage (1 day), a dense Al₂O₃ passive film formed on the coating surface, providing excellent substrate protection, with a corrosion current density of only 1.77 µA/cm² and a maximum charge-transfer resistance (R₂) of 652 Ω·cm². In the middle stage (8 days), Cl⁻ permeated through the cracked film, triggering selective dissolution of Al, while Si was enriched in situ to form a porous residual layer; the corrosion current density (I_corr) sharply increased to 13.25 µA/cm², and R₂ dropped to its minimum of 156.6 Ω·cm². Corrosion products at this stage were mainly Al₂O₃ and SiO₂, accompanied by small amounts of iron oxyhydroxides and hydroxides, and local coating failure began to appear. During the later stage (10–20 days), the corrosion products evolved into γ-FeOOH, α-FeOOH, and Fe₂O₃, which, together with an amorphous SiO₂ gel network enriched at the interface, formed a dual-layer composite rust layer. R2 consequently recovered from 156.6 Ω·cm² at 8 days to 424 Ω·cm² at 20 days, indicating a reduced corrosion rate and entry into a stable inhibition stage. The critical failure mechanism is that Cl⁻ preferentially penetrates the surface of the Al₂O₃ passive film, disrupting the metastable state of the coating and thereby creating pathways for corrosive media intrusion. The findings of this study can provide technical support for the safe application of such as-received coatings in non-load-bearing components with heat and corrosion resistance requirements. Full article

Hot-press forming (HPF) steel is a promising lightweight material for automotive applications but suffers from oxidation and reduced corrosion due to high-temperature processing. Aluminized coatings, particularly Al-10Si, are widely used to mitigate this issue. However, HPF heat treatment can create brittle alloy layers with cracks, compromising retention and increasing corrosion risk. This study investigated the effects of Sr addition on the microstructure and corrosion resistance of Al-Si-coated HPF steel. Al-Si and Al-Si-Sr coatings were applied to steel substrates and subjected to heat treatment to produce heat-treated (HT) Al-Si and HT Al-Si-Sr samples. Sr addition refined and spheroidized eutectic Si particles, improved coating homogeneity, and mitigated vertical crack formation in the Al-Fe-Si intermetallic layer. The resulting dense, crack-free alloy layer effectively shielded the Fe substrate from corrosion. After heat treatment, Sr facilitated the formation of a fine lamellar microstructure and a dense, continuous oxide film, enhancing coating retention and sustaining barrier protection. These improvements significantly delayed corrosion propagation into the Fe substrate. Corrosion resistance was evaluated using salt-spray tests (ASTM B117), potentiodynamic polarization, and electrochemical impedance spectroscopy in 3.5 wt.% NaCl solutions. Microstructural analyses revealed that even minimal Sr content (0.05%) considerably enhanced the performance of Al-Si coatings, demonstrating industrial applicability. This study highlights the potential of Sr-added Al-Si coatings in addressing the demand for lightweight and corrosion-resistant materials in the automotive industry, offering a viable solution for high-performance and environmentally sustainable applications. Full article

Accurate prediction of the stacking fault energy (SFE) is critical for controlling deformation mechanisms, specifically transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), in high-manganese (high-Mn) austenitic steels, which are of growing importance in automotive and structural applications that demand exceptional strength–ductility combinations. This study presents a systematic comparative evaluation of six supervised machine learning (ML) models—Multiple Linear Regression (MLR), Random Forest (RF), Extra Trees (ETs), Gradient Boosting (GB), Support Vector Regression (SVR), and a stacking ensemble—trained on a curated, outlier-cleaned experimental database of Fe-Mn-C-Si-Al-Cr-Ni-N spanning SFE values from 5.0 to 63.0 mJ/m² (mean 23.7 ± 11.2 mJ/m²). After Z-score outlier removal (|Z| > 3) and 80/20 train–test splitting with nested 5-fold cross-validation hyperparameter optimization using GridSearchCV, ET and GB achieved training R² values of 0.988 and 0.990, respectively, confirming that SFE is highly predictable from alloy composition alone. The stacking ensemble delivered the best generalization on the independent held-out test set (test R² = 0.603, RMSE = 5.60 mJ/m², MAE = 4.86 mJ/m²), outperforming all the individual learners. Random Forest feature importance analysis identified Al (22.3%), Fe (20.5%), and Mn (17.7%) as the three most influential compositional variables, collectively explaining 60.6% of the predicted variance. Pearson correlation analysis confirmed that Al was the strongest individual linear predictor (r = +0.421, p < 0.001), whereas Fe showed a significant negative correlation (r = −0.327, p < 0.001). Mn, C, and the remaining elements showed no statistically significant linear correlations with SFE, underscoring the dominance of nonlinear compositional interactions. Composition–SFE design maps derived from the GB model delineate the TRIP/TWIP regime boundaries in the Mn–C and Mn–Al composition spaces, providing a validated computational tool for targeted high-Mn steel alloy design. Full article

Wire Arc Additive Manufacturing (WAAM) has emerged as a promising additive manufacturing technique due to its high deposition rate and low material cost. WAAM is increasingly adopted in various industries for the production of large-scale metal components, yet optimizing productivity without sacrificing mechanical integrity remains a critical challenge, particularly for low-carbon steels. This study systematically investigates the influence of key WAAM parameters—welding current (100–350 A) and travel speed (5–30 mm/s) on the deposition stability, microstructure, and mechanical properties of thin walls made of low-carbon Fe–0.09 C–1.10 Cr–1.47 Mn–0.59 Si–0.56 Mo–0.11 Ni–0.23 V steel. A stable processing window for defect-free wall fabrication was established for currents of 100–250 A, while higher currents of 300–350 A resulted in melt pool instability and geometrical distortions due to excessive heat input. Microstructural characterization revealed a dual-phase structure consisting of allotriomorphic ferrite (ALF) and acicular ferrite (AF) in all samples. The microstructural evolution was critically governed by variations in the cooling time in the critical temperature range of 800 °C to 500 °C (t_8/5) within the thermal cycles, a direct consequence of the heat input quantified through volumetric energy density. Low heat input at 100 A, 5 mm/s promoted a microstructure with minimal ALF fraction of ~10%, whereas high heat input at 350 A, 30 mm/s induced significant ferrite recrystallization and coarsening, increasing ALF fraction to ~55%. These microstructural changes directly affected mechanical properties: YS/UTS decreased from 512 MPa/668 MPa to 401 MPa/602 MPa, respectively. Concurrently, the deposition rate increased substantially from ~1.6 kg/h to ~6.3 kg/h. The results demonstrate a critical trade-off between productivity and mechanical performance, providing a practical framework for parameter selection in WAAM-fabricated low-carbon steel components. Full article

Efficient joining of hard metals to steels is crucial for supporting sustainable manufacturing under emissions strategies to minimize CO₂. CoNiCrFeCu high-entropy alloy containing scandium (Sc) was designed as a filler for laser braze-welding of WC-Co and steel. The designed compositions with different Sc levels were melted and cast in a high-vacuum non-consumable arc furnace. The results showed that the as-cast microstructure was a complex mixture of a networked Ni₂Si, elongated Cr-Fe-Co solid-solution phase, and Fe-Ni-Co-Cu solid-solution phase. Scandium was shown to have formed compounds with nickel/cobalt and copper. The TG-DSC analysis confirmed that the melting points of the designed compositions were between 973.7 °C and 981.5 °C. The maximum spreading area of the CoNiCrFeCu-0.9Sc composition on AISI 1045 steel was 64.83 mm², and on the WC-Co cermet it was 78.63 mm². The interface between the fusion zone and AISI 1045 steel exhibited an epitaxial growth of dendrites from the steel base metal. The interface between WC-Co and the fusion zone exhibited a partial penetration of brazing filler into the Co matrix, forming a metallurgical bonding between the dissimilar materials. Sc, as an alloying element in the filler metal, enhanced the bond formation because it decreased the solidus temperature and increased wetting. Full article

With the rapid transition of power transmission systems toward higher capacity, longer distance, and improved efficiency, aluminum alloys from the 6xxx (Al–Mg–Si) and 8xxx (Al–Fe) series have become key structural materials for overhead conductors and power cables due to their low density, cost effectiveness, and favorable strength–conductivity balance. Compared with traditional steel-reinforced conductors, optimized aluminum alloy conductors can reduce structural weight by approximately 30–40% and installation cost by about 20–30%, while maintaining comparable current-carrying capacity. This review systematically focuses on modification methods and research progress of aluminum alloy cores for electric wires and cables. The strengthening characteristics of 6xxx alloys (heat-treatment responsiveness and precipitation strengthening) and the creep-resistance stability of 8xxx alloys are comparatively analyzed. Four core performance requirements—high electrical conductivity, mechanical strength, creep resistance, and corrosion resistance—are summarized as evaluation criteria for conductor applications. Particular emphasis is placed on three major modification strategies: (1) microalloying (e.g., Zr, Sc, rare earth elements) for precipitation and dispersoid stabilization; (2) thermomechanical process optimization for grain refinement and strength–conductivity balance; (3) composite reinforcement for high-temperature and ultra-high-strength applications. Quantitative literature data indicate that microalloying and process optimization typically achieve 15–40% strength improvement with conductivity variation within 3–5% IACS, while composite strategies may provide 30–80% strength enhancement but often at the expense of 5–20% conductivity reduction. The distinct applicability of 6xxx and 8xxx alloys under different service conditions is clarified, providing guidance for conductor material selection. Finally, future research directions—including precise composition–process integration, advanced thermomechanical control, and scalable modification technologies—are proposed to support high-performance, cost-effective, and large-scale deployment of aluminum alloy conductors. Full article

In this work, the effect of partial to complete Al substitution of Si on the microstructure, retained austenite (RA) stability, and mechanical properties of cold-rolled TRIP-aided steels was investigated. Four experimental TRIP-aided steels (Fe-0.2C-1.5Mn-1.5/1.0/0.5/0Si-0/0.5/1.0/1.5Al-0.025Nb, wt.%) were designed. The results indicate that replacing Si with Al significantly increases the volume fraction of soft polygonal ferrite (from 52% to 73%) and decreases that of bainite. Although the volume fraction of RA decreases (from 15.6% to 12.4%), its average carbon content and, consequently, its mechanical stability are enhanced, which suppresses the strain-induced martensitic transformation. In terms of mechanical properties, the substitution leads to a monotonic decrease in both yield strength (from 573 MPa to 536 MPa) and ultimate tensile strength (UTS) (from 839 MPa to 648 MPa), primarily due to reduced solid-solution strengthening, coarsened ferrite grains, and a weakened TRIP effect. Conversely, the total elongation (TEL) increases from 28.3% to 32.4%, attributed to the higher fraction of ductile ferrite. Consequently, the product of tensile strength and total elongation (PSE) exhibits a slight decline. The 1.5Si-TRIP steel exhibited the most balanced mechanical properties, achieving the highest PSE of 23.7 GPa·%. Full article

To address the high-salinity and hyper-humid thermal environment of tropical oceans and meet industrial demands for high strength and lightweight, austenitic low-density steel was developed as a novel corrosion-resistant steel. A 3.5 wt.% NaCl solution was used to simulate the marine environment to study the effect of Si on the corrosion behavior of this steel. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were employed to characterize the microstructures and corrosion behaviors of two test steels, as well as the phase compositions and element distributions of corrosion products after polarization and cyclic immersion accelerated corrosion tests. The results show that a dense oxide film initially forms on the steel surface in 3.5 wt.% NaCl solution at the early corrosion stage. Si addition induces SiO₂ formation and promotes Al conversion to Al₂O₃, enhancing oxide film compactness and inhibiting matrix atom outward diffusion and Cl⁻ inward penetration. With prolonged corrosion, the oxide film is dissolved or broken, forming a dense rust layer dominated by Fe₃O₄, Fe₂O₃ and FeOOH. Si enriches in the inner rust layer adjacent to the matrix and pitting cavities, inhibiting pitting deepening and promoting γ-FeOOH to α-FeOOH transformation, thus improving the steel’s corrosion resistance. Full article