The influence of varying Si and P contents on the corrosion behavior of sensitized 006Cr25Ni20 steel in boiling 65%(mass fraction) HNO₃ solution was investigated. The corrosion morphology and composition of the passive film were analyzed, along with microstructural observations. It was found that an increase in the Si mass fraction from 0.076% to 0.25% promoted the precipitation of M₂₃C₆ at the grain boundaries. As a result, a pitting-like intergranular corrosion morphology was induced by Cr-depleted zones along the grain boundaries. However, the M₂₃C₆ precipitates were discontinuously distributed and did not form a continuous network along the boundaries.Consequently, a significant increase in the depth of intergranular corrosion was not observed. When the P mass fraction was increased from 0.004% to 0.012%,the stainless steel exhibited a continuous trench-like intergranular corrosion morphology with a notable increase in corrosion depth. Concurrently, the polarization resistance of the passive film decreased, and the proportion of Cr₂O₃ within the surface passive film was reduced, leading to a significant deterioration in corrosion resistance.

Sulfur (S) and phosphorus (P), as typical harmful impurities in steel materials, significantly influence the forming quality and service performance of welds in advanced steel materials. In terms of forming, S affects the shape and contour of the weld pool by altering its flow characteristics and surface tension, while P primarily modifies the surface tension of the molten metal, thereby influencing the spreading behavior and wettability of the weld pool on the base material. In terms of performance, S readily forms low-melting-point sulfide inclusions that accumulate at grain boundaries, not only increasing susceptibility to hot cracking but also severely degrading the toughness and plasticity of the weld metal. P, on the other hand, undergoes significant grain boundary segregation during solidification, weakening the bonding strength of grain boundaries. This serves as a source for crack initiation and propagation and significantly reduces the toughness and strength of welded joints. This article reviews the impact of S and P elements on weld formation and performance based on the latest research and summarizes current control strategies for both elements.

To facilitate the construction of new-type power systems and achieve carbon peaking/carbon neutrality goals, new-generation coal-fired peak-shaving units have been extensively deployed, exposing key high-temperature components to damage mechanisms dominated by creep-fatigue interaction. Based on current design codes and material test data including P91/P92 etc., this study systematically investigates temperature, stress, and load variations in boiler thick-walled components under both steady-state and flexible peak-shaving operations. Comparisons reveal critical discrepancies between laboratory high-stress creep/fatigue testing conditions and actual low-stress service environments with frequent load fluctuations. The mechanisms governing how stress levels, temperature ranges, and load variation parameters such as amplitude, frequency and ramping rate influence creep void evolution, fatigue crack propagation, and coupled creep-fatigue damage are thoroughly elucidated. Results demonstrate that transient thermal stresses and localized plastic strains intensify substantially under peak-shaving conditions, causing a paradigm shift in dominant failure modes from time-dependent creep failure under steady-state operation to complex damage patterns dominated by low-cycle thermal fatigue and creep-fatigue interaction. The proposed countermeasures, informed by engineering failure cases, encompass the adoption of advanced alloys such as G115 and C630R for their superior creep-fatigue resistance, geometric optimization to mitigate stress concentration, and the implementation of online life-assessment systems. Crucially, establishing near-service creep-fatigue interaction test protocols, developing multi-factor coupled damage models, and formulating material selection guidelines tailored for peak-shaving units are identified as essential strategies to ensure long-term operational safety and reliability.

A high magnetic field, as an emerging non-contact high-energy physical field, can regulate metal solidification through multiple mechanical, magnetic and energetic effects, including Lorentz force, thermoelectromagnetic force, magnetization force, magnetic torque and magnetocrystalline anisotropy energy, without altering the chemical composition of materials, thus offering a new route for improving solidification structures and material properties. The research progress on solidification behavior and microstructure evolution of metals under high magnetic fields is systematically reviewed. The various magnetic field types and their basic modes of action are introduced, and their effects on fundamental physical properties such as electrical resistivity, wettability, diffusion coefficient, phase transformation temperature and magnetic susceptibility are summarized. From thermodynamic and kinetic perspectives, the regulatory mechanisms of magnetic fields on melt flow, momentum transfer, solute migration and solid/liquid interface stability are analyzed. The influences on composition segregation, solidification morphology, columnar-to-equiaxed transition, grain refinement, crystallographic orientation and second-phase particle morphology are further summarized. Existing studies indicate that various magnetic effects are coupled with temperature, flow, solute and interface evolution fields, and their dominant roles are jointly governed by magnetic field intensity, direction and gradient, temperature gradient, solidification rate and alloy magnetic susceptibility. Finally, it is proposed to establish quantitative criteria for the competition and synergy of multiple magnetic effects, to develop data-driven prediction and high-temperature in-situ characterization techniques under high magnetic fields, and to promote the engineering application of magnetic-field-assisted solidification.

The mechanism of diffusion bonding between martensitic stainless steel 00Cr12Ni10MoTi and a novel copper alloy Cu3Cr1.5Nb using Ni foil and AgCu37.5 as interlayers is investigated. Vacuum diffusion bonding was conducted at 980 ℃for 90 min under a pressure of 5 MPa. The microstructures and mechanical properties of the joints were systematically characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and tensile test. The results indicate that all three types of joints achieved interfacial metallurgical bonding to varying degrees. The direct diffusion-bonded joint exhibited a discontinuous interface with a tensile strength of 476.36 MPa and a dimpled fracture surface, characteristic of ductile failure. In the joint with the AgCu37.5 interlayer, Ag diffused toward the Cu side and segregated along the grain boundaries of the steel substrate, resulting in microcracks and Kirkendall voids due to the wetting and spreading of the filler metal. This joint fractured within the weld zone under tension, showing a tensile strength of 479.61 MPa, corresponding to a 0.7% increase, and a mixed ductile-brittle fracture mode. In contrast, the joint with the Ni foil interlayer demonstrated excellent metallurgical bonding on both sides, forming ductile solid solutions, Cr₃Ni₂ intermetallic compounds, and Kirkendall voids. It achieved a tensile strength of 491.38 MPa, representing a 3.1% improvement, and fractured in the copper substrate with clear dimples, indicating ductile fracture. Therefore, the use of a Ni foil interlayer enables sufficient interfacial bonding and superior joint performance in the diffusion bonding of stainless steel to copper alloy.

With the continued advancement of the dual carbon strategy, the proportion of scrap steel in steelmaking raw materials has been increasing continuously. The presence of residual elements such as Cu, Sn, Sb, and N in scrap steel, and their effects on steel processing, particularly on hottearing susceptibility, have become critical issues restricting the efficient recycling of scrap.The sources and classification of residual elements in scrap steel melting and their behavioral characteristics during the melting process are systematically summarized. On this basis, the major theories of hottear formation are reviewed, and the applicability and limitations of various hottearing prediction criteria are compared. Emphasis is placed on the segregation behavior, precipitation characteristics, and influence mechanisms of four typical residual elements (Cu, Sn, Sb, and N) during steel solidification. Specifically, Cu tends to segregate at grain boundaries to form low-melting-point phases, thereby widening the brittle temperature range. Sn and Sb exhibit a strong tendency for grain-boundary segregation, significantly reducing intergranular cohesion. N alters hottearing susceptibility through the formation of nitrides or by affecting the solidification path. Finally, the current research deficiencies in control strategies for residual elements under high scrap ratios, interactions among multiple elements, and in situ characterization techniques are discussed.

Residual stress-induced abnormal grain growth (AGG) is a key mechanism responsible for the formation of severe mixed-grain structures in nickel-based alloys. The surface coarse-grain ring, a common microstructural defect in small-diameter rolled bars, is often attributed to this mechanism. Using a GH4202 alloy rolled bar with high initial residual stress in the surface region,the microstructural evolution during solution treatment under both high and low initial residual stress conditions was investigated. Through EBSD/SEM characterization and theoretical analysis, the formation mechanism of surface coarse-grain ring defects was systematically elucidated. The results indicate that residual stress significantly influences the AGG process but is not a necessary condition. Under high surface residual stress, localized static recrystallization occurs first at the edge of the bar during solution treatment, triggering three-stage AGG and ultimately leading to the formation of a severe coarse-grain ring. When the initial residual stress is reduced, a shallower coarse-grain ring still develops through two-stage AGG. In both cases, the core mechanism of coarse-grain ring formation involves AGG initiated by the interplay between initial grain size (which provides the curvature driving force) and carbide pinning force, with residual stress playing a facilitating role. Therefore, eliminating coarse-grain ring defects requires emphasis on adjusting pre-solution grain size or regulating the pinning force magnitude. Accordingly, process improvement measures are proposed.

Strip casting, as a short-process steel manufacturing technology aligned with China’s dual carbontarget, offers significant advantages in energy conservation and carbon emission reduction. However, the interfacial behavior during sub-rapid solidification in strip casting differs fundamentally from that in conventional continuous casting. This complexity is particularly pronounced in high-value-added advanced steel grades with intricate alloying systems, where interfacial phenomena (deposited film, wetting, and heat transfer) are closely coupled with solidification. Frequent surface cracking has thus become a critical bottleneck restricting its large-scale industrial application.The current research status of interfacial behavior during sub-rapid solidification of molten steel in strip castingis systematically summarized in this review, with emphasis on the influencing mechanisms of specific alloying elements on deposited film formation as well as interfacial wetting and heat transfer. Subsequently, the research progress on surface quality of typical advanced steel grades is reviewed, focusing on the specific surface quality issues encountered in high-strength steels, weathering steels, and other grades with relatively mature industrial development. Finally, future directions for surface quality control in strip casting are prospected. It is proposed that a deeper understanding of the intrinsic links among interfacial behavior, phase transformation, and crack formation, along with synergistic optimization of interfacial and solidification processes, represents the key pathway toward improving surface quality.

Variable-composition delayed pouring is widely adopted as a key technique for mitigating macrosegregation in large steel ingots. However, its action mechanism and influence rules of process parameters have not been fully clarified. Based on a self-developed numerical model for macrosegregation, systematic analyses are performed on macrosegregation behaviors under various process parameters of delayed pouring. It is demonstrated that the degree of central positive segregation in ingots is gradually reduced with the extension of pouring delay time, increase of composition difference between ladles and rise of riser pouring height. Meanwhile, the composition gradient in the transition zone affected by the process is intensified, and local compositional inhomogeneity is aggravated accordingly. Further analyses reveal that downward liquid flow along the interface is generated at the solidification front during delayed pouring. The transport rules of solutes within the molten pool are altered, and the local distribution of temperature and solutes is rapidly reconstructed. In addition, local remelting at the solidification front is induced by the inflow of high-temperature molten steel with low solute content. For the design of delayed pouring processes, the control effect on central positive segregation, compositional uniformity of the transition zone and stability of the solidification front shall be comprehensively considered. Precise regulation of macrosegregation in large steel ingots can thereby be achieved.

FeCrNiCoMo cryogenic stainless steel is recognized as a promising material for aerospace and cryogenic applications due to its exceptional strength and toughness at cryogenic temperatures. Regarding the oxygen enrichment phenomenon in the additive manufacturing of stainless steel, the effects of adding two oxide-forming elements (aluminum and titanium) on the oxide characteristics, microstructural evolution, and mechanical properties of stainless steel was analyzed. It was found that Ti-based oxide additives resulted in superior performance relative to Al-based systems, exhibiting finer oxide dispersion and more refined cellular structures after manufacturing. After homogenization treatment, the additively manufactured stainless steel demonstrates a significant improvement in mechanical properties. Upon addition of titanium as a harmless oxide-forming element, the material attains a yield strength of 1 208 MPa and a tensile strength of 1 245 MPa, accompanied by a cryogenic impact toughness of 82 J. In contrast, the aluminum-added stainless steel exhibits a significantly lower cryogenic impact toughness of only 59 J, representing an approximate 39% enhancement in the titanium-added system. It indicates that for high-strength and tough steels that are sensitive to inclusions during additive manufacturing, the mechanical properties of the materials can be effectively improved by optimizing the selection and utilization of oxide-forming elements.

Fe-Cr-Ni-Mo-Co maraging stainless steel for cryogenic service is known for its excellent combination of room-temperature strength and low-temperature impact toughness. However, welding of this steel is challenging. When the internal stress generated by the welding process is too high, it is prone to causing hot cracks during the welding. To prevent such defects, it is necessary to incorporate an appropriate amount of δ-ferrite into the weld deposit structure. Yet, an excessive amount of δ-ferrite severely deteriorates the low-temperature impact toughness of the weld. Therefore, it is necessary to optimize the alloy composition to ensure that the precipitation amount of δ-ferrite in the weld seam falls within a reasonable range, thereby suppressing the formation of hot cracks without significantly deteriorating the low-temperature impact toughness of the weld seam.A special welding wire specifically for Fe-Cr-Ni-Mo-Co maraging low-temperature stainless steel was obtained through composition design. The precipitation mechanism of δ-ferrite in the weld deposit structure was studied, and the content of δ-ferrite in the weld wire coating structure was regulated through alloy composition optimization design, so that the proportion of δ-ferrite in the weld coating structure was controlled within the range of 3% to 4%. Ultimately, the low-temperature toughness at -196 ℃ was improved to 58 J, the room temperature strength was increased by 20%, and the coefficient of the welded joint was not lower than 0.9.

The metallographic microscope, X-ray diffraction, electron backscatter diffraction, scanning electron microscope and transmission electron microscope were employed to investigate the influence of the heat treatment consisted of austenitizing at various temperatures for 2 h followed by quenching, then -73 ℃ deep cryogenic treatment for 1 h, and finally 160 ℃ low-temperature tempering for 2 h. The results show that the prior-austenite grain size of the experimental steel increases with the raising austenitizing temperature, which grows slowly from 9.8 to 19.8 μm between 950 and 1 050 ℃, and then rapidly from 38.6 to 121.0 μm between 1 075 and 1 200 ℃. The grain-coarsening temperature is determined to be 1 075 ℃. The main precipitates are M₂₃C₆ carbides and M₂(C,N) carbonitrides, whose dissolution temperatures are 1 000 and 1 100 ℃, respectively. Dissolution of these precipitates accelerates grain growth and simultaneously enhances the strength and stability of austenite. Re-dissolution of C, N, Cr and Mo lowers the M_s temperature, resulting in incomplete austenite-martensite transformation; retained austenite content reaches approximately 80% (volume fraction) when austenitized above 1 075 ℃. The key method to reduce the volume fraction of retained austenite in the experimental steel involves controlling the quenching heating temperature at around 1 000 ℃, combined with cryogenic treatment and low-temperature tempering. This process achieves an ideal state with retained austenite content below 5% (volume fraction), hardness of at least 58.0HRC, and a coefficient of linear expansion of less than 1.2×10^-5 ℃^-1, thereby meeting the stringent requirements of bearing steel with high hardness and high dimensional stability.

In traditional manufacturing processes for duplex stainless steels, an increase in ferrite phase content is often accompanied by grain growth, which limits the enhancement of strength. This study utilized powder metallurgy-hot isostatic pressing (PM-HIP) to fabricate a 25Cr-type low-nitrogen duplex stainless steel. While ensuring fine grain sizes in both phases, the ferrite phase content is adjusted through subsequent solution heat treatment. The relationship between microstructural evolution and mechanical properties was systematically investigated, revealing a ferrite-dominated strengthening mechanism. The results showed that the microstructure of initial powder consisted of pure ferrite, while the sintered compact exhibited a dual-phase matrix of austenite and ferrite containing σ phase. Solution treatment at 1 050 ℃ for 30 min effectively eliminated the σ phase. As the solution temperature increased from 1 050 to 1 200 ℃, the average ferrite grain size increased from 9 to 18 μm, and the yield strength improved from 547 to 768 MPa. The significant increase in the ferrite phase fraction led to a multiplicative rise in the nitrogen content within the more readily yielding austenite phase, driving synchronous strengthening of both phases and ultimately resulting in a remarkable enhancement of yield strength.

Flat porous submerged entry nozzles serve as core equipment for high speed thin slab continuous casting. Increasing the number of outlet holes of such nozzles can guarantee molten steel supply, yet it complicates the flow field inside the mold and exerts influences on heat transfer, solidification and solute transport. To reveal the action laws of nozzle structures, a three-dimensional numerical model coupled with fluid flow, heat transfer, solidification, solute transport and constant background magnetic field is established for the thin slab continuous casting process of Q235B steel. The effects of four-hole and five-hole nozzles on flow field, temperature field, shell growth and carbon segregation under different casting speeds are analyzed. It is demonstrated that jet distribution and recirculation structures are remarkably altered by the hole number and spatial layout of nozzles. More outlets and smaller inner cavity volumes are equipped in five-hole nozzles, so stronger multiple jets are generated under identical casting speeds. A peak flow velocity of approximately 1.6 m/s is measured at the position 0.4 m below the meniscus for five-hole nozzles, which exceeds the 0.9 m/s obtained with four-hole nozzles. Lateral flows produced by five-hole nozzles facilitate the delivery of superheated molten steel to the lower mold and narrow faces, high-temperature zones near the nozzles are shrunk, and temperature uniformity in regions close to the narrow mold faces is improved simultaneously. Shell growth is significantly affected by casting speeds. Thinner shells are formed at the mold outlets for both nozzle types with rising casting speeds, and more drastic variations are observed when four-hole nozzles are adopted. Carbon segregation is governed jointly by molten steel flow, heat transport and solute accumulation. Positive segregation zones are formed at solidification fronts under the scouring action of molten steel. The peak segregation positions of five-hole nozzles are gradually shifted downward with increased casting speeds, while peak segregation values are maintained within the range of 1.20—1.22 and barely disturbed by casting speed elevation. In conclusion, the matching of rational porous nozzle structures and high casting speed process parameters contributes to optimized flow field configurations inside molds, stable shell thickness at mold outlets and alleviated central segregation.

Driven by the advancement of major equipment and energy engineering, the market demand for ultra-large metal castings keeps rising in fields including nuclear power, shipbuilding, wind power, metallurgy and heavy machinery, with stricter standards imposed on their internal quality and mechanical properties. To clarify the solidification mechanism of ultra-large steel ingots, a three-dimensional multiphase solidification model coupling columnar grains, equiaxed grains and liquid phase is adopted to simulate the cooling and solidification behaviors of a 303 t 16Mn steel ingot. Established on a volume-averaged multiphase framework, flow, heat transfer, solute transport and equiaxed grain number density equations are solved within the model. Molten steel flow, equiaxed grain migration, solute redistribution at solid-liquid interfaces and latent heat release induced by solidification phase transformation during ingot solidification are quantified, and predictions for multiphase solidification processes involving columnar and equiaxed grains are realized. The equiaxed grain nucleation mechanism triggered by the fragmentation of high-order dendrite arms is incorporated into the model, and solidification and remelting phenomena occurring during equiaxed grain transport are calculated. Highest cooling rates are detected at the bottom and sidewall regions of the steel ingot, and rapid growth of columnar grains is accelerated accordingly. Massive equiaxed grains are generated via dendrite arm fragmentation near solidification fronts. Dense equiaxed grains sink under gravitational force and accumulate at the ingot bottom. Microstructural transformation from columnar grains to equiaxed grains is facilitated by this mechanism, and an inverted triangular equiaxed grain zone is formed at the ingot bottom. Distinct influences on macrosegregation distribution are exerted by equiaxed grain distribution. Solute-depleted equiaxed grains are concentrated at the ingot bottom, and negative segregation is generated at this position. Molten liquid enriched with solute elements floats continuously throughout solidification, and severe positive segregation is formed along the ingot central axis and adjacent to the top riser. Channel segregation is also predicted to develop near the riser region. The simulated distributions of macrosegregation and solidification microstructures are matched with distribution laws acquired from ingot dissection experiments and previously published experimental data.

DP590 high-strength dual-phase automotive steel enjoys extensive application. Under increasingly severe service environments, homogeneity defects of rolled products induced by internal quality flaws in cast slabs have become prominent, and continuous casting soft reduction technology serves as an effective technical route to address such issues. Aiming at internal defects including central porosity, central shrinkage cavities and intermediate cracks in continuous casting slabs of DP590 dual-phase automotive steel, numerical simulation and thermal simulation tests are integrated, and thermal states and microstructure evolution laws of cast slabs under various reduction amounts are systematically analyzed to determine the reasonable control range of soft reduction amounts. Results are demonstrated that the effect of soft reduction can be efficiently transmitted to the central zone of cast slabs. When the reduction amount is raised from 0 to 18 mm, the temperature at central nodes of cast slabs is decreased by 0.633 ℃, and the central solidification process is accelerated to a certain extent. Meanwhile, deformation fluctuations at slab centers are increased remarkably, and risks of initiation and propagation of central cracks are elevated accordingly. Through analysis on distribution laws of stress and strain, stress concentrations on slab surfaces are mainly concentrated at corner regions, stress levels on outer arcs are obviously higher than those on inner arcs, and strain values of inner arcs are significantly larger than those of outer arcs. With the increase of reduction amount, overall stresses on both inner and outer arcs of cast slabs are raised synchronously, and strain growth amplitudes of inner arcs are particularly remarkable. Uneven deformation along the slab width direction is therefore triggered, and asymmetric slab broadening is generated. Thermal simulation tests are further verified that solidification microstructures of cast slabs can be effectively refined by soft reduction technology, and obvious influences are exerted on the precipitation behavior of massive ferrite. At the position 1/4 slab thickness away from the inner arc, the optimal uniformity of solidification microstructures is obtained under a reduction amount of 9 mm, and the generation of intermediate cracks in cast slabs can be effectively restrained.

To address the difficulty in measuring and predicting the spatial distribution of inclusion compositions in continuous casting blooms, a 280 mm×380 mm bloom produced in an industrial steel plant is selected as the research object. The Brody-Fleming segregation equation was coupled with thermodynamic and kinetic models for inclusion composition transformation. The equilibrium partition coefficients of nine elements are calculated using FactSage and fitted as linear functions of liquid fraction. On this basis, a coupled model is established, by which the three-dimensional spatial distributions and dynamic evolution of dissolved element contents in steel and inclusion contents during continuous casting are simultaneously predicted with an improved description of elemental thermodynamic properties. The results show that the model is able to characterize the spatial distribution features of solute elements and inclusion contents during continuous casting with good accuracy. At 27 m below the meniscus, the calculated total sulfur mass fraction in the central region of the continuous casting bloom is approximately 0.007%, the total aluminum mass fraction is about 0.003 8%, and the dissolved aluminum mass fraction reaches roughly 0.002 64%. Owing to the differences in dissolved element contents at different positions in the bloom, the evolution of inclusion compositions also exhibits obvious spatial non-uniformity. At the bloom edge, the calculated inclusion contents are close to the measured results. Within the bloom interior, the calculated contents of Al₂O₃, CaO, CaS and SiO₂ are in good agreement with the measured values, whereas the calculated MnS content in the bloom center is higher than the measured result. Because of the thermodynamic characteristics of MgO, the calculated and measured results are mainly close in magnitude, while differences still exist in their spatial distribution patterns. Overall, the element contents calculated by the model are in good agreement with the experimental measurements.

Disqualification in water immersion ultrasonic inspection induced by inclusions frequently occurs for premium bearing steel one-hot rolled rods manufactured via the continuous casting billet one-hot rolling process. The sources and formation mechanisms of such defects are systematically investigated starting from refining and casting processes, and effective control measures based on molten steel flow regulation inside the mold are proposed. Correlative analyses of inspection defect zones on rolled products, inclusion characteristics in molten steel during smelting and continuous casting billets, and chemical compositions of nozzle clogging deposits are performed. Large-sized chain-shaped Mg-Al-(Ca)-O composite inclusions distributed inside rolled rods are identified as the dominant trigger for unqualified water immersion ultrasonic inspection results. Indigenous Al₂O₃ and MgO-Al₂O₃ inclusions in molten steel are accumulated on inner walls of the submerged entry nozzle to form clogging deposits during casting. Detached clogging agglomerates fail to achieve sufficient floatation inside the mold, and such inclusions are subsequently inherited from continuous casting billets to finished rolled rods. Insufficient floatation efficiency of separated clogging materials is caused by unreasonable flow field distribution within the mold. Structures of submerged entry nozzles are therefore optimized through a combination of 1:1 physical modeling and numerical simulation. An upward-inclined four-side-hole submerged entry nozzle is developed accordingly. Uniform and active molten steel flow fields inside the mold are generated and the floatation and removal of inclusions are promoted by the designed nozzle without abnormal mold level fluctuation and slag entrapment. After continuous casting with this optimized nozzle, the qualification rate of water immersion ultrasonic inspection for premium bearing steel one-hot rolled rods is raised from 62% to more than 95%.

How to control Al₂O₃ oxide inclusions in Al-deoxidized steel has long been a challenging issue in metallurgical production. Calcium treatment can modify high-melting-point Al₂O₃ oxide inclusions into low-melting-point calcium aluminate (12CaO·7Al₂O₃), which effectively inhibits nozzle clogging and improves the hydrogen-induced cracking resistance of steel. However, parameters such as the timing and method of calcium addition directly affect the calcium yield and the degree of inclusion modification. Improper control may, on the contrary, exacerbate the nozzle clogging phenomenon. Therefore, the modification effect of calcium treatment on non-metallic inclusions in Al-deoxidized steel is reviewed. From the perspectives of kinetics and thermodynamics, the mechanism of action and key influencing factors are elaborated, including the effects of molten steel temperature, calcium addition method and timing, CaO/Al₂O₃ ratio of refining slag, as well as the contents of O, S and Al in molten steel on the compositional evolution and liquid phase fraction of inclusions. In addition,the technological optimization directions of calcium treatment is discussed, aiming to improve calcium utilization efficiency and inclusion control level, involving innovative approaches such as secondary calcium treatment, application of calcium-silicon iron, and calcium-magnesium alloy synergism.

Coke powder, as the primary fuel in sintering production, has a particle size distribution that significantly affects both product quality indicators and energy consumption levels. The current method for measuring coke powder particle size typically involves manual sampling, drying, and vibrating sieving, which is complex, time-consuming, and unsuitable for timely control of crushing and proportioning systems. Although image recognition technologies for online detection of moving material particle sizes are developing rapidly, the fine particle size of coke powder and the harsh conditions in crushing and proportioning processes lead to severe challenges for image acquisition and size recognition. To address these issues, an image acquisition system for complex industrial environments was developed. The system comprises an image acquisition chamber and a multi-stage dust removal pipeline, designed to minimize the effects of lighting, temperature, and dust on image capture. Considering the fine particle characteristics of coke powder, an improved neural network was used for multiple training rounds to optimize the particle size recognition model, enabling the identification of surface particle size distribution on the conveyor belt. A predictive model was then constructed using machine learning algorithms, combining image-recognized surface particle size distribution data with manually sieved results to train a model capable of predicting the overall particle size distribution, thereby enhancing recognition accuracy. This image acquisition and particle size recognition system has been put into application in the coke powder crushing workshop of a domestic iron and steel enterprise. The application results showed that the recognition errors of the system for the particle size distribution ratio of coke powder in four intervals of (0, 0.5), [0.5, 3), [3, 5) and [5, ∞) mm were all less than 3%.

The burn-through point (BTP) state directly impacts critical production indicators of sintering processes, including yield, quality, and energy consumption. Addressing the limitations of current BTP prediction methods in terms of temporal span and operational adaptability, a hybrid long-term prediction approach integrating convolutional neural networks (CNN) and long short-term memory (LSTM) networks is proposed. The CNN module extracts localized temporal patterns across features from input data, while the LSTM component models temporal dynamics, collectively capturing long-range dependencies within the dataset to enable early BTP prediction during the material charging and ignition phases. Experimental and practical applications demonstrate that the model achieves a mean absolute error of less than 0.4 wind-box segments within a 45 min prediction window, with 89.2% prediction accuracy within ±0.8 wind-box segments. An effective solution for long-term BTP prediction challenges is provided.

As marine equipment is gradually extended to deep sea and polar cold regions, higher requirements are imposed on low-temperature strong toughness and service reliability of heavy-section offshore engineering steel. To address the critical problems of easily coarsened core microstructure and inferior toughness in heavy steel plates, oxide metallurgy technology that submicron non-metallic inclusions are adopted to induce heterogeneous nucleation of acicular ferrite has become a core approach for optimizing core microstructure and mechanical properties. Nevertheless, collision and agglomeration of various inclusions readily occur during solidification in practical large-section continuous casting, forming large-size harmful particles. Uniform and dispersed distribution of fine inclusions is destroyed by this phenomenon; the steel matrix is also separated, and fatigue cracking is thereby triggered. Dual objectives including removal of large-size harmful inclusions and refinement as well as uniform dispersion of small-size beneficial inclusions cannot be simultaneously achieved by existing chemical modification methods and physical purification processes developed based on Stokes’ law. Aiming at the urgent and unresolved difficulty in homogeneous regulation of inclusions, a novel method is proposed for regulating homogeneous distribution of inclusions during molten steel solidification via pulsed current based on the driving theory of current density gradient, and regulation mechanisms of pulsed current on uniform distribution of inclusions are systematically investigated. Key parameters determining migration efficiency of inclusions are verified to be pulsed current frequency. Severe central inclusion segregation in cast slabs can be eliminated by pulsed current, and uniform and dispersed distribution of non-metallic inclusions over the full cross-section of cast slabs is realized, as further validated by industrial continuous casting trials. Meanwhile, remarkable reductions in average inclusion size and obvious increases in the proportion of fine inclusions are observed after treatment with pulsed current. Local Joule heating effects induced by bypass current in micro-regions at inclusion interfaces are responsible for such variations. Surface energy of inclusions is reduced by the above effects, wettability of molten steel against non-metallic inclusions is improved, thermodynamic barriers for collision and coalescence between inclusions are elevated accordingly, and collision-induced growth of inclusions is suppressed ultimately.

Because of its special geometric structure, the multi-strand asymmetric tundish is easy to lead to significant differences in the flow characteristics of each flow of molten steel, which in turn affects the consistency of slab quality. Taking the four-strand asymmetric tundish currently used in a Chinese steel plant as the research object, the effects of different diversion walls and diversion holes on the flow field and temperature field of the tundish were studied. Firstly, the flow field characteristic parameters of tundish with different schemes were compared by physical simulation. The deficiency of tundish structure (original scheme P) was pointed out, and the optimization scheme was put forward accordingly. The temperature field distribution and inclusion removal effect of the optimization scheme were further analyzed by numerical simulation. The physical simulation results show that after using the optimized A4 scheme, the average residence time of the tundish is 53 s longer than that of the original scheme, and the proportion of dead zone is reduced from 37% to 28%. Among them, the stagnation time of No.1 nozzle is extended from 9 to 33 s, the short-circuit flow phenomenon is eliminated, and the consistency of each flow is significantly improved. The numerical simulation results show that the flow field and temperature field distribution of the A4 scheme are more uniform, the temperature difference at each outlet is reduced from 6 to 1 ℃, and the removal rate of inclusions of different sizes is better than that of the original scheme. In summary, the metallurgical function can be effectively improved by optimizing the structure of the tundish, which provides a technical basis for improving the quality uniformity of the slab.

The effect of the quenching-partitioning-tempering (Q-P-T) process on the microstructure evolution laws and regulation mechanisms of mechanical and forming properties for cold-rolled Q&P980 steel at 285, 310 and 335 ℃ quenching temperatures has been investigated. The results indicate that increasing quenching temperature promotes the transformation of martensite morphaology from coarse blocky structures to uniformly distributed fine laths. The volume fraction of retained austenite and its carbon content exhibit a trend of first increasing and then decreasing, with the optimal mechanical properties achieved at a quenching temperature of 310 ℃. An increase in quenching temperature leads to a decrease in hole expansion rate,plastic strain ratior-value, and limiting forming curves, while the plastic anisotropy index(Δr-value) shows an upward trend. At a quenching temperature of 285 ℃, strong recrystallized {111} texture and high-angle grain boundaries weaken the planar anisotropy caused by grain orientation differences, resulting in the best forming performance. Quenching at a temperature of 335 ℃ resulted in the deterioration of the material′s formability, which is attributed to the presence of a strong α-fiber texture coupled with a decrease in the intensity of the γ-fiber texture. It is indicated that while there is a certain correlation between forming performance and mechanical properties, more attention should be paid to the influence of texture types and their microstructural distribution on forming performance.

In order to reduce carbon emissions and realize the efficient recovery of zinc and iron elements in metallurgical dust, it is very important to carry out thermodynamic analysis of the reaction system of metallurgical dust under hydrocarbon atmosphere. The effects of different process parameters (such as temperature and time) on the metallization rate and dezincification rate of metallurgical dust were studied by high temperature roasting test system. The regulation mechanism of temperature on phase evolution and microstructure was revealed by means of X-ray diffraction (XRD) analysis method and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) technology, and then the separation mechanism of zinc and iron under the synergistic effect of carbon and hydrogen was clarified. The results show that the migration process of zinc-containing phase under the coupling effect of carbonand hydrogen is mainly divided into two processes. Below the boiling point of zinc ( 907 ℃), ZnFe₂O₄ is basically reduced to ZnO, and when the temperature is above 907 ℃, the phase transition from ZnO to Zn (g) occurs rapidly under the interaction of carbon and hydrogen. The research results show that when the reduction temperature is 1 050 ℃, the duration is 20 min, the carbon-oxygen ratio (C/O) of blast furnace bag ash to converter sludge is 0.8, and a reduction atmosphere of H₂∶CO∶CO₂∶N₂=6∶2∶1∶1 is adopted, both the metallization rate and the zinc removal rate of metallurgical dust reach the optimal values. In addition, due to the different expansion coefficientsamong minerals when hydrogen is used to reduce iron oxide, thermal stress is easily generated at the interface, resulting in the formation of cracks. On the other hand, with the continuous consumption of H₂, the carburizing reaction is intensified, the CO production is increased, and the vapor pressure inside the spherical nucleus is increased, which eventually leads to the rupture of spherical nucleus anda large number of cracks. With the progress of the reaction, cracks are gradually deepened, and the emergence of cracks promotes the reduction of zinc and iron oxides.

Iron ore pellet production is recognized as an energy-intensive and high-emission industrial process, and its energy conservation and emission reduction represent a critical component for the iron and steel industry to achieve the “dual carbon” goals. Efforts are made herein to leverage the synergistic effect of high-pressure roll grinding pretreatment and optimized ore blending, thereby reducing the pellet induration temperature while ensuring product quality, so as to provide technical support for the green transition of the iron and steel industry. A systematic laboratory experimental approach was adopted. Firstly, six types of iron concentrates were pretreated using a high-pressure roll mill under a pressure of 14 MPa, and the effects of this process on raw material particle size, specific surface area and pelletizing performance were analyzed. Subsequently, green pellets were prepared by a disc pelletizer, and the preheating and induration processes were simulated in a horizontal tube electric furnace to explore the influence law of different process parameters on pellet strength. Finally, scanning electron microscopy was employed to analyze the microstructural changes of pellets, thus revealing the synergistic strengthening mechanism.Results demonstrate that high-pressure roll grinding can significantly improve the physical properties of iron concentrates. After two passes of roll grinding treatment, the proportion of the 5 mm size fraction in the blended ore can be increased to 75.45%, which effectively enhances particle surface activity and strengthens recrystallization interface reactions, thereby improving pellet strength. Meanwhile, two passes of high-pressure roll grinding can substantially reduce the pellet induration temperature from 1 200 to 1 100 ℃. On this basis, optimized ore blending was further applied to enhance pellet consolidation efficiency. Under the optimal ore blending ratio (5 wt.% ore A, 11 wt.% ore C and 7 wt.% ore D), the minimum induration temperature of pellets can be further reduced to 1 080 ℃, with the compressive strength reaching 3 189 N/P, which far exceeds the industrial standard of 2 500 N/P. Microstructural analysis indicates that the synergistic effect of high-pressure roll grinding and optimized ore blending significantly enhances the recrystallization and intergrowth degree of hematite, reduces internal pores and cracks of pellets, and thus greatly improves structural compactness. The synergistic mechanism of high-pressure roll grinding and optimized ore blending was clarified, and the dual optimization effects of this combined technology on reducing induration temperature and improving pellet strength were quantified via laboratory data.

The low thermal expansion properties of invar steel make it widely used in precision instruments, aerospace components and other fields, but the low strength limits its further development. Adding alloying elements to invar steel and inducing the precipitation of carbide second phase through solid solution-aging can significantly improve the mechanical properties of invar steel.Solid solution-aging is a key prerequisite for precipitation, and carbide dissolution behavior in this process is particularly important. The alloying elements Nb, Mo, V and Ti were added to invar steel, and the carbide dissolving behavior was analyzed and the mechanism was investigated by scanning electron microscopy and high-temperature laser confocal microscopy. The results show that there are two types of carbides in Nb-Mo-V-Ti and Nb-Mo-V invar steels. The larger carbide particles with an average size greater than 5 μm, formed during the solidification process, are called as the primary carbides. The smaller carbides with an average size of less than 1 μm, precipitated from the matrix, are called as the secondary carbides. Both types of carbides are compositeprecipitation phasesof (Nb, Mo, V)C or (Nb, Mo, V, Ti)C corresponding to their respective components. The thermodynamic results and HT-CSLM observation indicate that the dissolution temperature of the primary carbides is close to the solidification transition temperature of the invar steel, so that it is difficult to dissolve. The secondary carbides realize the basic dissolution after heating and prolonging the holding time, and from this, Ti has a hindering effect on the dissolution of the carbides, which makes the carbides have a higher thermal stability. In addition, the Johnson-Mehl-Avrami-Kolmogorov equation is used to characterize the dissolution kinetics of the secondary carbides, and the dynamics model is experimentally verified to be able to predict the dissolution fraction of the secondary carbides better.

The advancement of rolling technology relies on robust technical support, while the current control level has entered a critical turning point. The control effect based on traditional control theories has approached its limit, and numerous key technical problems have not yet been completely resolved. Therefore, it is imperative to introduce brand-new control theories and methods to achieve leapfrog improvement in control performance. In the hot-rolled strip production process, the automatic gauge control of the finishing rolling process occupies a core position, and its control accuracy directly determines the quality and qualification rate of the finished strip. To address the influence of temperature fluctuations on the stability of the exit thickness of incoming materials and the positive feedback problem existing in the traditional gauge feedback control, a hardness feedforward control strategy is proposed. Taking the Ansteel 1700 ASP production line as the application object, the influence coefficients of load distribution on various process indicators are calculated and analyzed; meanwhile, based on the increment equations of thickness, rolling force and crown, the roll gap adjustment values of the F₃—F₆ stands are determined. In hot rolling field practice, the hardness feedforward control of the F₃ and F₄ stands and the hardness over-compensation control of the F₅ stand are successfully realized. In addition, a nonlinear PID control strategy is introduced into the monitoring AGC system, which features a wide parameter tuning range and strong engineering practicability. Statistical analysis of production data of different rolling specifications shows that after the implementation of the composite control strategy, the strip thickness accuracy is improved by approximately 1% compared with the original level, indicating that the control system has good prospects for popularization and application.

Invar alloys, known for their extremely lowlinear expansion coefficient and excellent soft magnetic properties, have been extensively applied in precision optics, microelectronics, magnetic shielding and aerospace industries. Ultra-thin Invar alloy strip products are focused, as they are regarded as essential for high-end applications such as fine metal masks and precision electro-mechanical components. The state-of-the-art fabrication techniques, including electroforming, precision cold rolling and subsequent surface-quality enhancement processes, are systematically summarized with a comparative discussion of their manufacturing mechanisms, technical advantages and existing limitations. Moreover, key performance optimization strategies such as texture tailoring, annealing parameter control, pulsed-current-assisted treatment and hydrogen-based annealing are comprehensively reviewed to elucidate the underlying strengthening and soft-magnetic enhancement mechanisms of Invar alloy strip.Researchers are paying increasing attention to the critical role of high-purity alloys in ensuring surface defect-free and dimensional stability in ultra-thin products, which has now become a key bottleneck.Overall, the findings reveal that precise control of process parameters, high-cleanliness smelting, and multi-performance synergistic optimization is the key to enabling superior ultra-thin Invar alloys.

To address the issues of segregation and microstructural inhomogeneity in Inconel 718 alloy ingots produced by dual vacuum melting at a domestic enterprise, the melt pool evolution, dendrite characteristics, and elemental segregation during vacuum arc remelting, as well as the dissolution behavior of Laves phase and Nb diffusion kinetics during homogenization, were systematically investigated using finite element numerical simulation, thermodynamic calculation, and microstructural characterization. The results indicate that during vacuum arc remelting, the melt pool morphology changes from an initial shallow flat shape to a stable U-shape; the extension of the mushy zone leads to gradual coarsening of dendrite size from the ingot surface to the center. Nb and Mo exhibit obvious positive segregation in the interdendritic regions, and the ingot shows non-uniform features with deteriorated structure at the top and aggravated segregation at the center, with the maximum Nb segregation coefficient reaching 2.86 in the top-center area. During homogenization, the Laves phase dissolves progressively and the Nb distribution becomes more uniform. Kinetic analysis reveals that the volume fraction of Laves phase decays exponentially with homogenization time. By optimizing the two-step homogenization treatment, the residual segregation index of Nb is reduced from1.00 (as-cast) to 0.14.The optimal homogenization regime was ultimately determined to be 1 160 ℃ for 20 h, followed by heating to1 180 ℃ and holding for 45 h. The established residual segregation index model can provide a theoretical basis for optimizing the homogenization process of Inconel 718 alloy.The final alloy bars exhibit a dense and uniform microstructure without obvious macro-defects, with an average grain size of 8-10.5 grade, and the tensile properties at room and elevated temperatures, stress-rupture properties, and impact toughness all exceed the national standard requirements.

Under the strong impetus of the global“dual-carbon” strategy, the green transformation of the metallurgical industry is imperative. Blast furnace smelting technology with a high pellet ratio has emerged as a key research focus.High-silicon magnesium flux pellets is concentrated, examining their current research status and development trends. Pellets demonstrate significant advantages in low-carbon environmental protection. Their production entails low energy consumption and minimal pollutant emissions. Featuring high iron grade, uniform particle size, and low sulfur content, pellets create favorable conditions for low-carbon and stable blast furnace operation.It effectively advances the energy conservation and emission reduction efforts in the steel industry. High-silicon magnesium flux pellets exhibit distinctive characteristics. Utilizing high-silicon iron ore expands resource options and reduces costs. MgO enhances slag fluidity, facilitating desulfurization. Furthermore, flux pellets contain inherent flux components, which lower costs and improve pig iron quality. However, in blast furnace smelting with high pellet proportions, noticeable changes occur in burden distribution as the pellet ratio increases. The characteristics of the softening-melting zone also alter. Although the melting-dripping performance improves, the temperature of the softening-melting zone rises and its width expands, thereby disrupting gas flow. The slag system is significantly influenced by pellet composition. Variations in gangue elements such as silicon and magnesium modify the slag system’s composition and properties, consequently affecting desulfurization efficiency. Synthesizing existing research, blast furnace smelting technology with high pellet ratios, while promising, still confronts numerous challenges. Future research should prioritize optimizing pellet production processes, precisely regulating blast furnace operational parameters and innovating burden structure design. These efforts will establish a technical foundation for the sustainable development of the steel industry and contribute to the steady realization of the “dual-carbon” goals.

Aiming at the degradation mechanism of coke induced by K, Na, KF and NaF gases during blast furnace smelting, gas adsorption experiments on coke were conducted via the gas-phase adsorption method. Combined with characterization techniques including XRD and SEM-EDS, the influence laws of K, Na, KF and NaF gases on the hot-state properties and microstructures of coke were systematically investigated. The results show that coke surface particles are exfoliated under the action of K gas, while powder-like spalling of coke surface is induced by Na gas. In contrast, the number of pores in coke is significantly increased by KF and NaF gases. After the adsorption of K, Na, KF and NaF gases by coke, the interplanar spacing of the (002) crystal plane of graphite microcrystals is enlarged, whereas the microcrystalline stacking height and microcrystalline layer size are reduced, which severely impairs the orderliness and integrity of the microcrystalline structure. The degradation degree of the aforementioned gases on the microcrystalline structure is ranked as follows: K>Na>KF>NaF. The variation of microcrystalline structure leads to an increase in coke porosity, which in turn elevates the coke reactivity index (CRI) and reduces the coke strength after reaction (CSR). Among these gases, the effects of K and Na gases on coke porosity are significantly stronger than those of KF and NaF gases. Specifically, the influence of K gas is greater than that of Na gas, and the impact of KF gas exceeds that of NaF gas. When coke is adsorbed with 1% NaF gas, its hot-state properties (with CRI≤25% and CSR≥65%) still meet the requirements for blast furnace smelting. However, after the adsorption ofmass fraction of 1% K, Na, or KF gas, both CRI and CSR exceed the standard limits. Overall, the influence degree of various gases on the hot-state properties of coke follows the sequence: K>Na>KF>NaF. In addition, with the increase in gas adsorption capacity, the growth rate of CRI and the decline rate of CSR both exhibit a trend of marginal decrease.

Against the backdrop of the low-carbon transition in the iron and steel industry, double challenges including energy consumption imbalance and slag cost out-of-control are confronted in converter steelmaking with a high scrap ratio. To address the problems of unstable slag addition control and large energy consumption calculation deviation in 120 t converters under high scrap ratio conditions, the thermal-material-oxygen coupling relationship during converter steelmaking is analyzed, and the intrinsic correlation mechanism among molten pool heat demand, slag consumption and thermal compensation under high scrap ratio conditions is clarified. Key production data from 1 200 heats are integrated through data preprocessing, and an integrated prediction and optimization system for the optimal slag addition amount, which combines mechanism models and intelligent algorithms, is established. Eight key characteristic parameters such as molten steel weight and hot metal silicon content are screened out by means of Pearson correlation analysis combined with recursive feature elimination algorithm, and comparative and optimization studies are carried out on BP neural network, PSO-BP and GA-BP models. The results show that the GA-BP model exhibits the optimal performance, with the mean absolute percentage error of 0.13% and the root mean square error of 208.03 for slag addition amount prediction. The model has been successfully applied in the production site with favorable prediction effects, and effective technical support can be provided for the green and efficient production of converter steelmaking with a high scrap ratio.

To investigate the influence law ofdefocusing amount on the microstructure and properties of laser welded joints of 2 mm thick Q235 steel sheets, metallographic microscope, scanning electron microscope, tensile testing machine, microhardness tester and electrochemical workstation were used to systematically characterize and analyze the welded joints. The experimental results showed that with the defocusing amount changing from negative to positive values, the width of the weld zone and heat-affected zone gradually increased. The hardness of the welded joint first increased and then decreased, while the self-corrosion current density and self-corrosion potential first decreased and then increased. The average tensile strength also exhibited a trend of first increasing and then decreasing. When the defocusing amount was 0 mm, the average hardness of the weld zone reached the maximum value of 170.03HV, the average tensile strength was the highest at 299.83 MPa, the self-corrosion current density was the smallest at 1.39×10^-5 A/cm², and the capacitive reactance arc radius was the largest, indicating the optimal corrosion resistance.

In view of problems such as large scale differences, complex textures and difficult identification of tiny defects on the surface of strip steel, which lead to low detection accuracy, an improved detection algorithm named DMI-YOLO based on YOLOv8n is proposed, aiming to enhance the multi-scale feature extraction capability and small target detection accuracy. Firstly, a lightweight feature extraction module called C2f-DWRB is constructed. The perception capability for defects of different scales is enhanced through the introduction of multi-scale dilation-wise residual and dilated reparam block structures. Secondly, a modulation fusion module is embedded into the neck network. Local details and global semantic information are fused by means of an adaptive attention mechanism, thus strengthening the feature expression effect under complex backgrounds. Finally, Inner-EIoU is adopted in the prediction stage to improve the original loss function. The positioning robustness for tiny defects is enhanced through the optimization of the aspect ratio strategy. Experimental results show that the mean average precision of the improved algorithm reaches 80.3% on the NEU-DET dataset, which is 3.5% higher than that of the original YOLOv8n network. Meanwhile, the detection speed is maintained at 84.2 frames per second, with both the model size and computational complexity reduced to a certain extent. The proposed DMI-YOLO algorithm has both high accuracy and real-time performance in the task of hot-rolled strip steel surface defect detection and can meet the requirements of practical industrial applications.

Due to the large cross-sectional dimension and long solidification duration of extra-thick slab, the central segregation cannot be effectively alleviated by conventional external electromagnetic flow control technologies. As a novel electromagnetic flow control method regulating molten steel flow from inside to outside, electromagnetic swirling technology enables effective regulation of the initial flow field inside the mould. Industrial tests of electromagnetic swirling are carried out under the current of 600 A and frequency of 50 Hz for unsteady casting conditions at the last casting heat of a 450 mm extra-thick slab continuous caster in a domestic steel plant. Variation characteristics of molten steel flow patterns inside the mould before and after the application of electromagnetic swirling are investigated via multi-physics coupling numerical simulation. Test results demonstrate that central segregation of extra-thick slabs cast at the last heat can be remarkably improved by electromagnetic swirling technology, and segregation ratings are all restricted within C1.0. Under the effect of electromagnetic swirling, the initial jet flow inside the mould is presented as S-shaped dispersed flow with low velocity, uniform distribution, stable state and shallow impact depth, and erosion on the initially solidified shell can therefore be mitigated.

In order to study the high-temperature plasticity of low-temperature resistant H-beam steel used in marine engineering under different strain rates, high-temperature tensile tests were conducted on the Gleeble-3800 thermal simulation test machine for the continuous-casting billets of low-temperature resistant H-beam Q420NE steel for marine engineering applications at two strain rates of 0.01 and 1 s^-1. The variation laws of high-temperature strength, hot plasticity and fracture morphology of irregular-shaped continuous-casting billets were obtained in the temperature range of 600-1 300 ℃. The results showed that when the continuous-casting billets were stretched at a higher strain rate of 1 s^-1, the reduction of area of the specimens increased with the increase in tensile temperature, and the reduction of area was always greater than 65%. When high-temperature tensile tests were conducted at a lower strain rate of 0.01 s^-1, the test steel exhibited a significant third brittle zone, with a temperature range from 600 to 850 ℃, where the reduction of area was always less than 65%, indicating poor hot plasticity in this range. Overall, better hot plasticity could be obtained at higher strain rates. In addition, the overall fracture strength of Q420NE continuous-casting billets under deformation at the strain rate of 1 s^-1 was higher than that of 0.01 s^-1, which was consistent with the fracture morphology.

To address the insufficient prediction accuracy of silicon element yield in electric arc furnace steelmaking and the proneness of the traditional grey wolf optimizer(GWO) to local optima, a chaotic dynamic grey wolf optimizer(CDGWO) is proposed and an integrated prediction model is developed by integrating it with an auto-encoder(AE). Firstly, the AE is employed to reconstruct smelting data features and denoise them. Subsequently, the CDGWO algorithm is designed. Tent chaotic mapping is used for population initialization to enhance global search capability; a nonlinear convergence factor is formulated; a δ-wolf levy flight mechanism is introduced to enable escape from local optima during stagnation phases; and an adaptive leadership election mechanism based on historical performance and recent progress is established. Based on five base models of logistic regression, support vector machine, multi-layer perceptron, random forest and light gradient boosting machine, CDGWO is utilized to optimize the integration weights. Experimental results demonstrate that the CDGWO integrated model achieves a mean absolute percentage error of 11.28% on the test set, which is 1.03% lower than that of the original GWO integrated model. Shapley additive explanation interpretability analysis identifies that temperature, aluminum content, carbon content and manganese content are core influencing factors. Temperature and carbon content exert a negative effect on the yield, while aluminum and manganese contents show a significantly positive effect.

The direct sodium roasting process for vanadium extraction from vanadium-titanium magnetite, offering the advantage of high overall vanadium recovery, faces challenges such as excessive sodium salt consumption and difficult utilization of high-sodium tailings. A new process of vanadium extraction by sodium-calcium composite roasting is proposed. Through the synergistic effect of sodium carbonate and calcium carbonate, the amount of sodium salt can be reduced and the recovery rate of vanadium can be improved.Experimental results demonstrate that compared with traditional sodium roasting, the sodium-calcium composite system achieves a 3.29% increase in vanadium recovery (reaching 75.19%) after water leaching while reducing sodium salt dosage from 6% to 4%. Notably, the acid leaching process shows a remarkable 25.18% improvement in vanadium recovery (up to 97.08%) with sodium salt consumption decreased from 6% to 5%. This technology replaces 16.6%—33.3% of sodiumsalt by low-cost limestone, effectively reducing Na content in tailings from 2.360% to 0.032%—1.790% and residual V content from 0.240% to 0.029%—0.211%. The findings highlight the significant advantages of sodium-calcium composite roasting in reducing production costs, improving resource efficiency, and mitigating environmental risks.

In the KR hot metal pretreatment process, the vortex distribution formed by the rotation of the stirring paddle exerts a significant influence on desulfurization efficiency. To enhance the dispersion degree of desulfurizer and thus improve desulfurization efficiency, a three-dimensional numerical model is established to systematically investigate the three-dimensional distribution characteristics of the vortex at the top of the hot metal ladle and the multiphase flow field distribution rules inside the hot metal ladle under different stirring parameters. The accuracy of the established three-dimensional numerical model is verified by the measurement results of the water model. Results indicate that whether the bottom of the vortex reaches the top of the stirring paddle is a key factor affecting the flow pattern inside the hot metal ladle and the dispersion degree of desulfurizer. The fluid velocity inside the hot metal ladle increases with the rise in stirring paddle rotation speed, but the proportion of the dead zone at the bottom of the stirring paddle cannot be completely eliminated merely by increasing the rotation speed. The turbulent kinetic energy dissipation rate of hot metal is proportional to the square of the rotation speed. When the rotation speed is higher than 90 r/min, the turbulent kinetic energy dissipation rate is proportional to the immersion depth of the stirring paddle; when the rotation speed is lower than 90 r/min, the turbulent kinetic energy dissipation rate shows no obvious change with the increase in immersion depth. Based on the relational expressions among rotation speed, immersion depth and turbulent kinetic energy dissipation rate, as well as the relational expression between turbulent kinetic energy dissipation rate and vortex depth, a calculation formula for the critical rotation speed at which the bottom of the vortex reaches the stirring paddle under different immersion depthsis derived. This calculation relational expression of critical stirring parameters can provide theoretical guidance for matching reasonable rotation speed and immersion depth of the stirring paddle, thereby realizing the improvement of desulfurization efficiency.