High-sulfur iron concentrates emit SO2 into the flue gas during pellet induration. To investigate the effect of the SO2 cycle on pellet quality in the grate-kiln process, sulfur balance analysis, thermodynamic calculations, and pellet production experiments under simulated flue gas circulation conditions were conducted. The results indicated that SO2 circulation inhibited desulfurization and deteriorated pellet strength. SO2 absorption increased the pellet sulfur content to 0.70 wt.% during the downdraft drying phase, and the absorption could be aggravated by the moisture. The desulfurization rate of the preheating process was also decreased to 16.67%, resulting from the refractory sulfate generation. Sulfur content of the roasted pellets dropped to 0.13 wt.% because of the aluminosilicate generation. The finished pellet sulfur content further decreased to 0.08 wt.% due to the fresh air during the cooling process. Eventually, optimization measures were proposed when high-sulfur iron concentrates were used for oxidized pellet preparation.
With the proposal of China’s “Carbon Peaking and Carbon Neutrality” policy, the steel industry faces urgent pressure to transition toward green and low-carbon development. However, the persistent reliance on burden structure dominated by sinter and pellet in China has led to the high energy consumption and pollution emissions in process before ironmaking, which has increasingly become a major obstacle to the green development of the steel industry. Lump ore can be directly charged into blast furnaces without high-temperature roasting, making it a more environmentally friendly and cleaner raw material option. The utilization of lump ore in blast furnace not only has obvious economic advantages but also achieves significant energy saving and carbon reduction effects. Therefore, an overview of the application of natural lump ore resources was provided, with a focus on its metallurgical properties and the factors influencing them. It further analyzed and summarized strategies for optimizing lump ore performance, particularly highlighting the advantages and technical challenges associated with preheating treatments. Additionally, the application experience, changes in technical and economic indicators, as well as the effects of energy saving and carbon reduction under the condition of a high ratio of lump ore in actual production were elaborated in detail. The results show that after loading lump ore to blast furnaces, the raw material cost is reduced by approximately 50.88 CNY/t, and the CO2 emissions from the production of 1 t pig iron can be reduced by 51.18 kg.
Severe internal oxidation formed in advanced high-strength steels (AHSSs) during the hot-rolled coiling process compromises subsequent cold rolling and galvanizing processes. Herein, we report how Sn microalloying governs internal oxidation behavior and modulates iron oxide phase transition process. Sn addition significantly reduces the depth of grain boundaries oxidation and the area of internal oxidation, as well as retards the process of oxide scale transformation. Sn preferentially segregates at the iron oxide/substrate interface, forming a diffusion barrier that suppresses outward diffusion of alloying elements and inward oxygen transport. Concurrently, Sn enrichment at grain boundaries obstructs short-circuit oxygen diffusion pathways, significantly reducing the depth of oxidation at the grain boundaries. Furthermore, Sn segregation decreases the interfacial oxygen chemical potential and oxygen availability for selective oxidation reaction. The strategic incorporation of surface-active elements has emerged as a viable metallurgical approach to reduce internal oxidation in hot-rolled coils for AHSS applications.
As a distinctive unshaped refractory material used in steelmaking induction furnace linings, significant variations in raw material performance, particularly erosion resistance, have been observed across silica sources from different regions. To clarify the causes of performance discrepancies and reveal the erosion resistance mechanisms, erosion resistance experiments were conducted on three quartzite raw materials from distinct regions. Furthermore, the enhancement effects of mineralizers on the raw material with the poorest performance were investigated, and the erosion resistance mechanisms of representative raw materials and mineralization effects in silica ramming materials were proposed. The results demonstrated that the presence of dolomite and iron oxide in raw materials is critical for improving the erosion resistance of silica ramming materials. However, the material with 1 wt.% dolomite as a standalone mineralizer exhibited optimal erosion resistance compared to iron oxide composite mineralizers. This improvement is attributed to the formation of uniformly distributed tridymite and an appropriate liquid phase, which mitigates volume expansion effects caused by quartz phase transformation, thereby minimizing aggregate cracking. Additionally, magnesium derived from dolomite plays a specialized role in the operational environment, with the synergistic effects of these two factors collectively enhancing the material’s erosion resistance.
To investigate the dispersion and deposition behavior of the nanoparticles (NPs) in the molten steel under the combined effects of turbulent flow and Brownian motion, a 3D model utilizing volume of fluid-discrete phase model was developed based on a small-size ingot casting process. A modified Brownian motion model was implemented into the simulation using user-defined function to more accurately predict the motion behavior and distribution of the NPs in the molten steel. The results show that the NPs tend to deposit at the bottom or disperse toward the wall under the turbulent flow. The introduction of Brownian motion increases the horizontal dispersion rate (DH) to 21.3% and reduces the bottom deposition rate by 12.8%. A reduction in the particle size and density promotes higher particle mobility, characterized by increased velocity and DH, along with diminished deposition. As the particle size decreases to 1 × 10-7 m, Brownian motion becomes a significant factor influencing the particle dynamics. Additionally, increasing the initial velocity of the molten steel results in a lower DH of the particles. However, once the velocity exceeds 0.15 m s-1, its influence on the particle velocity becomes negligible.
In response to the challenges of inadequate predictive accuracy and limited generalization capability in data-driven modeling for the mechanical properties of the cold-rolled strip steel, a predictive modeling method named RFR-WOA is developed based on random forest regression (RFR) and whale optimization algorithm (WOA). Firstly, using Pearson and Spearman correlation analysis and Gini coefficient importance ranking on an actual production dataset containing 37,878 samples, 22 key variables are selected as model inputs from 112 variables that affect mechanical properties. Subsequently, an RFR-based predictive model for the mechanical properties of cold-rolled strip steel is constructed. Then, with the combination of the coefficient of determination (R2) and root mean square error as the optimization objective, the hyperparameters of RFR model are iteratively optimized using WOA, and better predictive effectiveness is obtained. Finally, the mechanical properties prediction model based on RFR-WOA is compared with models established using deep neural networks, convolutional neural networks, and other methods. The test results on 9469 samples of actual production data show that the model developed present has better predictive accuracy and generalization capability.
Phosphorus tends to migrate into metallic iron during the direct reduction of high-phosphorus oolitic iron ore, leading to undesirable phosphorus enrichment in metallic iron. However, the underlying reduction and migration mechanisms remain poorly understood. Phosphorus behavior during coal-based reduction was systematically investigated through theoretical modeling and experimental approaches. Thermodynamic analysis revealed that the carbon reduction of solid Ca3(PO4)2 to gaseous P2 requires temperatures exceeding 1400 °C. Notably, this threshold significantly decreases to 1130.5 °C in the presence of SiO2 and Al2O3. Further investigations demonstrated that Ca3(PO4)2 co-reduces with FexOγ in the presence of SiO2-Al2O3-FexOγ, forming Fe3P (instead of gaseous P2) at a markedly lower temperature of 778.7 °C. Mechanistic studies indicate that the inherent thermal stability of Ca3(PO4)2 inhibits the generation of reactive [P2O5]. However, SiO2-Al2O3 coexistence destabilizes Ca3(PO4)2 while exponentially enhancing [P2O5] activity. This synergistic effect dramatically promotes the phosphorus mineral reduction. Characterization confirmed that Ca3(PO4)2 migrated into the slag phase (4FeO·Al2O3·3SiO2·CaO·P2O5). Subsequently, the reactive P2O5 in slag is reduced with metallic iron to form Fe3P, which further dissolves into the α-Fe matrix through solid-state diffusion, ultimately generating Fe-P solid solutions.
The dissolution of MgO-refractory into the slag had an obvious influence on the steel-slag reaction and the slag property, especially for high-aluminum steels. The dissolution behavior of MgO-refractory was investigated under various conditions, including the temperature, the initial steel composition, and the initial slag composition. A steel-slag-refractory kinetic model for high-aluminum steel was developed, which incorporated the process of MgO-refractory dissolution. The dependence of the MgO mass transfer coefficient krMgO on temperature T during MgO-refractory dissolution process was established, as described by kMgOr=-63,754/T+24.38524. It was indicated that the MgO dissolution rate was significantly influenced by the temperature. A higher temperature increased the dissolution rate of MgO. The initial steel composition had a slight impact on the MgO dissolution rate. Additionally, the initial slag composition strongly impacted the MgO saturation concentration and the dissolution rate. A lower initial Al2O3/SiO2 ratio increased the MgO dissolution rate. The steel-slag-refractory kinetic model accurately predicted the dissolution of MgO-refractory and the influence of dissolved MgO on the viscosity and composition change during steel-slag-refractory reactions. It was suggested that a higher temperature can hardly reduce the viscosity due to the dissolution of the MgO-refractory.
The physicochemical properties of SUS304 foil surfaces are crucial to their applications. Pulsed laser modification was applied to 30 μm thick SUS304 foils to systematically investigate the influence of laser energy on surface characteristics. Through multidimensional characterization of surface morphology, three-dimensional profiles and roughness, contact angle, and chemical composition, the structure-function correlation between laser energy and the physicochemical properties of steel surface was revealed. With increasing laser energy, the surface morphology of the steel transitions from a directional rolling-marked structure to a uniform sponge-like isotropic structure, accompanied by increased peak density and an expanded interfacial area. Additionally, the chemical state on the metal surface gradually stabilizes from unstable redox reactions, forming a stable oxide layer and significantly increasing active hydroxyl groups, thereby effectively improving surface wettability. Single lap shear tests reveal an enhancement in the bonding strength of steel/carbon fiber reinforced composites joints after laser modification, which is attributed to the synergistic effects of mechanical interlocking, enhanced wettability, and chemical bonding at the interface. The demonstrated potential of laser surface treatment for modifying SUS304 ultra-thin foils provides theoretical support and technical reference for its application in fiber metal laminates.
Rare earth elements are widely used in steel production due to their unique metallurgical properties, which can modify inclusions, improve the cleanliness of molten steel, and optimize steel properties. However, high activity also makes rare earth elements prone to intense chemical reactions with refractories during the smelting process, which can not only accelerate the erosion and failure of refractories, but also reduce the cleanliness of molten steel owing to the formation of secondary inclusions. Therefore, it is essential to understand the interaction mechanisms between rare earth steels and refractories. Herein, the research progress on the interactions between rare earth steels and refractories is systematically reviewed. Based on both laboratory studies and industrial applications, emphasis is placed on the reaction mechanisms and their effects on the stability of refractories and the cleanliness of molten steel. At the same time, the prevention methods are summarized, including the refractory optimization, protective coatings for nozzles, argon blowing, and the application of external electric fields. Furthermore, the applicability and limitations of these methods are analyzed. Finally, future research directions are discussed to address the limitations of current studies, focusing on the development of novel refractories, non-contact control methods, and digitally intelligent process control.
To reveal the influence mechanism of Nb/Ti microalloying on the mechanical property of ferritic stainless steel, the grain size, phase composition, microhardness, mechanical properties and fracture morphology are characterized and analyzed for ferritic stainless steel with single addition of Ti stabilizing element and composite addition of Nb and Ti stabilizing elements. The influence mechanism of Ti and Nb stabilizing elements is elucidated on microstructure and mechanical properties of ferritic stainless steel. Results indicate that the grains are bigger (20-60 µm) for ferritic stainless steel containing 0.09 wt.% Ti (F-Ti-ss). The average grain size is about 43.9 µm. Meanwhile, there are many granular TiN precipitates with big size. For ferritic stainless steel with Nb and Ti stabilizing elements (F-Nb-Ti-ss), the grains are small (8-22 µm), and average grain size is about 17.3 µm. There are a few granular TiN precipitates with small size. Furthermore, many nanoscale (Fe, Cr, Nb)C phases precipitate at grain boundary, which plays a role in refining grain size. Compared with mechanical properties of F-Ti-ss (506 MPa and 28.2%), both the ultimate tensile strength and elongation are improved for F-Nb-Ti-ss (573 MPa and 30.5%). The ultimate tensile strength is increased by 13.2%. The main reason is that grains are obviously refined and a large number of nanoscale phases precipitate at grain boundary for F-Nb-Ti-ss. Therefore, strengthening effect is obvious and grain deformation is more uniform during tensile test.
The high-temperature dissolution behavior of carbides during the quenching process significantly influences grain growth, mechanical properties, and secondary carbide precipitation, thereby playing a major role in the heat treatment process of die steel. This study investigated the changes in carbide type, particle size distribution, and weight percentage in DC53 steel after holding at 1060 °C for 2 h, followed by oil quenching. The analysis was conducted using Thermo-Calc, DICTRA computations, and experimental methods including electron backscatter diffraction, transmission electron microscopy and laser particle size analysis. The experimental results showed that four types of carbides (M7C3, M6C, M23C6, and MC) existed in DC53 steel before quenching. After quenching, M23C6 carbides were almost entirely dissolved, while the other three types partially dissolved into the matrix. The volume-weighted geometric mean size of carbides ($\overline{x}$ geo,3) increased from 5.43 to 15.15 μm, and the weight percentage decreased from 13.03% to 5.01%. Small-sized carbides (below 5 μm) dissolved more readily, which primarily accounted for the reduction in carbide weight percentage during quenching. In contrast, the weight percentage of large-sized carbides (greater than 10 μm) varies less. DICTRA computations indicated that M7C3 carbides smaller than 7 μm can completely dissolve into the matrix after holding at 1060 °C for 2 h. The findings provide an effective reference for optimizing carbide control during the heat treatment process of DC53 steel.
Acid is commonly used to separate phosphorus-containing solid solutions from steelmaking slag. However, the acid leaching solution obtained from this process cannot be directly utilized and thus requires purification. The effect of different conditions on the calcium and iron removal characteristics of modified steelmaking slag leaching solution was investigated. Additionally, the removal mechanism was analyzed by thermodynamic calculations. The results indicated that the addition of soybean straw ash in steelmaking slag modification enabled K2O to enter the phosphorus-containing solid solution, promoting phosphorus enrichment. Valuable elements such as phosphorus and potassium were more easily dissolved in the mixed acid. The oxalic acid concentration had a significant effect on the calcium removal rate, whereas the effects of temperature, stirring rate, and time on the calcium removal rate were minor. The main component of the calcium removal precipitate was CaC2O4·H2O, with a removal rate up to 94.48%. During the iron removal process, when the pH value of the solution was low, Fe3+ mainly reacted to form the iron hydroxide precipitate for removal. Increasing the pH value of the solution would cause Fe3+ to combine with \({\text{H}}_{2}{\text{P}}{\text{O}}_{4}^{-}\), forming FePO4·2H2O precipitate, leading to a reduction in the phosphorus content of the leaching solution.
A calcium zirconate crucible material with excellent performance was prepared by fixing the particle size proportion and exploring the addition of Y2O3. The results show that Y3+ solid-dissolves into c-ZrO2 to occupy the Zr4+ positions, leading to structural defects and promoting the sintering of calcium zirconate. Adding 0.5 wt.% Y2O3 into calcium zirconate can enhance the modulus of rupture, reduce the thermal expansion coefficient, and improve the thermal shock resistance. Through high-temperature test, it is found that adding 0.5 wt.% Y2O3 significantly improves the corrosion resistance of the sample.
The electric arc furnace (EAF) offers advantages in energy savings, environmental protection, and high efficiency by using scrap as the primary charge and utilizing a high-temperature electric arc as the main heat source for steel smelting. The improvement of EAF smelting efficiency is primarily influenced by three key factors: the heat transfer efficiency of the electric arc, the intensity of molten pool stirring, and the melting rate of scrap. The arc heat transfer efficiency determines the energy input efficiency and the maximum smelting temperature of the EAF. Molten pool stirring intensity plays a crucial role in ensuring uniformity in temperature, composition, and flow within the furnace, preventing the formation of dead zones. The scrap melting rate is a decisive factor in EAF smelting efficiency, largely governed by the coupling of heat and mass transfer. Thus, understanding not only the rapid melting mechanism of scrap but also the impact of arc heat transfer and molten pool stirring is essential to optimizing the smelting process. Advancing research in these areas is critical for shortening the EAF smelting cycle, reducing energy consumption, lowering costs, and improving resource utilization. Therefore, recent achievements and development trends in fundamental research on enhancing EAF smelting efficiency were summarized.
The refractory composition of submerged entry nozzles (SEN) critically governs interfacial reactions, which in turn determines the onset of clogging. The interfacial reactions between two Al2O3-C refractories with 8.7 and 1.7 Al2O3/SiO2 ratios and Al-killed steel were studied through laboratory experiments. The flow of molten steel relative to the inner wall of the SEN was simulated by rotating a refractory rod in high-temperature molten steel. For the Al2O3-C refractory with an 8.7 Al2O3/SiO2 ratio, an Al2O3 reaction layer was formed at the steel/refractory interface as the reaction progressed, which initially grew to 780 μm before thinning to 470 μm. Concurrently, the refractory surface became entirely coated with both clustered and plate-shaped Al2O3 inclusions following 120 min of reaction. For the Al2O3-C refractory with a 1.7 Al2O3/SiO2 ratio, a continuous Si-Al-Fe-O liquid reaction layer was generated at the steel/refractory interface, which significantly impeded the physicochemical interactions between the molten steel and refractory. The composition of the reaction layer evolved sequentially from the Si-Al-Fe-O liquid phase to the Si-Al-O solid phases with the increasing reaction time. After 120 min, the refractory surface became fully coated with clustered Al2O3 inclusions. Compared to the Al2O3-C refractory with a 1.7 Al2O3/SiO2 ratio, the Al2O3-C refractory with an 8.7 Al2O3/SiO2 ratio was more likely to capture Al2O3 inclusions in the steel during its contact with Al-killed steel. The current experiment results indicate that in Al-killed steel continuous casting operations, Al2O3-C-based SEN with an 8.7 Al2O3/SiO2 ratio should have a higher clogging potential than Al2O3-C-based SEN with a 1.7 Al2O3/SiO2 ratio under equivalent casting conditions.
Low heat input welding is widely used in the industry. The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input. The impact toughness, microstructure and failure mechanisms of the coarse-grain heat-affected zone (CGHAZ) in a micro-alloyed steel were investigated by welding thermal simulation with the heat input ranging from 15 to 65 kJ/cm. The impact toughness of CGHAZ is highly sensitive to variations in low heat input. The failure mechanisms were discussed from the viewpoints of micro-voids formation and micro-cracks propagation. The micro-voids are preferred to be formed and grow at soft phase of grain boundary ferrite (GBF). At the heat inputs no more than 22 kJ/cm, martensite was dominantly formed, and the micro-cracks initiated from the GBF were propagated into the grain interiors, leading to the brittle fracture and low toughness. When the heat input was increased to 31.2 kJ/cm, granular bainite became the dominant constitute, causing cracks to deflect away from GBF and propagate into prior austenite grains. The high density high-angle and low-angle grain boundaries and the presence of retained austenite, effectively restricted the crack propagation, resulting in ductile fracture behavior and enhanced toughness. High heat input (62.3 kJ/cm) promoted coarse GBF formation, providing continuous paths for microcrack propagation. This direct intergranular crack progression caused brittle fracture and low toughness. Industrial cold cracking in the CGHAZ can thus be controlled by heat input optimization to maximize toughness.
The corrosion wear behavior of the selective laser melting (SLM) and forged TC4 alloys in 3.5 wt.% NaCl solution is studied. Results indicate that the current densities of the two TC4 alloys increase with the increase in applied potential, meaning that the corrosion resistance of the alloys decreases. And the main product of the passive film is TiO2. What’s more, corrosion wear behavior is more severe due to the presence of corrosion, resulting in greater mass losses and deeper wear scars. To explore the interaction between corrosion and wear for the two TC4 alloys, the change of the mass loss proportions for wear caused by corrosion and corrosion caused by wear with potential is analyzed. The mass loss of wear caused by corrosion cannot be ignored, and it affects SLM TC4 alloy with the unique acicular α′-phase significantly.
In view of the frequent deterioration of molten steel quality during the tundish filling process, the slag-steel-air interface behavior in a tundish, including liquid level fluctuation, slag eyes, slag entrapment and air suction during the steady-state casting and filling process, was comparatively studied through physical modeling and mathematical simulation methods. During the filling process, the liquid surface forms a large-size slag eye under the impact of molten steel from a ladle shroud, which simultaneously results in a violent fluctuation of liquid level. Concurrently, the liquid flow entrains the air phase and the cover slag into the tundish impact zone, resulting in slag entrapment and air suction. At filling flow rates of 1.5Q, 2.0Q, and 2.5Q (Q is the flow rate under steady-state casting), the amount of slag entrapped is 8.39 × 10-5, 9.65 × 10-5, and 12.7 × 10-5 m3, respectively, while the volume of air aspirated is 0.84 × 10-4, 1.47 × 10-4, and 2.01 × 10-4 m3, indicating that slag entrapment and air suction intensify with an increase in tundish filling flow rate. Flow field characterization identifies eddy currents in the impact zone as the primary driver of the above phenomena. Proper filling process parameters were proposed to improve the steel quality during the tundish filling.
Nickel-based superalloys demonstrate exceptional mechanical strength stemming from their unique γ/γ′ microstructure. Understanding microstructural state effects on the strength of GH4742 superalloy is critical for mechanical performance. The investigation of GH4742 superalloy samples with controlled microstructure was conducted via a methodology combining tailored thermomechanical processing, heat treatment, and strengthening mechanism modeling. The γ + γ′ duplex structure achieves an optimal strength-ductility synergy, exhibiting yield strength of 805 MPa, ultimate tensile strength of 1440 MPa, and elongation of 21%. Comparatively, samples containing fine single-modal γ′ precipitates exhibit marginally reduced performance, while mixed-grain structures containing grain boundary-localized columnar γ′ precipitates demonstrate severe property degradation (yield strength of 582 MPa, ultimate strength of 1007 MPa, elongation of 12%). Quantitative analysis indicates that mechanical responses are predominantly governed by multimodal γ′ precipitate distributions and their synergistic precipitation strengthening effects. Notably, the γ + γ′ duplex structure exhibits exceptional strengthening efficacy, with precipitation strengthening mechanisms contributing 670.83 MPa to its overall strength.
Exploiting effective approaches to achieve superior ductility has consistently been a topic of widespread interest in refractory multi-principal-element alloys (RMPEAs). Herein, we developed a one-step forming method, electron-beam directional-solidification (EB-DS), to fabricate an equiatomic Hf-Nb-Ta-Zr RMPEA, and compared its microstructures as well as mechanical properties with those of the as-cast alloy fabricated by levitation induction melting. EB-DS method can transform the equiaxed grain microstructures in the as-cast alloy to columnar grain microstructures as well as eliminate the slight segregation. The room-temperature tensile test demonstrates that the ductility is substantially improved from 3.9% for the as-cast alloy to 23% for EB-DS alloy, accompanied by the slight enhancement in yield strength from 946 to 991 MPa. The microstructural investigations indicate that EB-DS alloys with columnar grains present a significantly optimized coordinated plastic deformation between the grain boundary region and the grain interior region, leading to the suppression of cracking along grain boundaries.
Conventional lightweight refractory materials with low bulk density and more pores suffer from harsh corrosion and erosion in actual applications. A type of lightweight Al2O3-MgAl2O4 aggregates with a core-shell structure was synthesized at 1750 °C using a rolling granulation method. Microstructural evolution and properties of the spherical aggregates were systematically studied. Scanning electron microscope and X-ray computed tomography results confirmed that a continuous and dense MgAl2O4 spinel shell structure with a thickness of 200-300 μm was formed on the surface. The corrosion results indicated that the corrosion index of the core-shell aggregates exhibited a 60% enhancement when compared to Al2O3 spherical. Moreover, Al2O3-MgAl2O4 refractory materials, which are based on the lightweight Al2O3-MgAl2O4 spherical aggregates, possessed a higher temperature modulus of rupture of 9.19 MPa, and the retention rate of residual flexural strength reached 70% after thermal shock testing. The above results showed an improvement of 129.75 and 44.28% compared with pure Al2O3 aggregate samples, respectively. In addition, the MgAl2O4 spinel shell could trap the Mn, Fe elements from infiltrated slag and transfer into (Mg, Fe, Mn) Al2O4 spinel, infiltrated CaO reacts with Sample Al2O3 matrix to form a calcium hexaluminate (CA6) isolation layer, and the above two reasons enhance the corrosion resistance of the material. The corrosion mechanism was elaborated in detail.
The high-temperature compressive deformation behavior of medium manganese steel using a four-roll reversible rolling mill is investigated, revealing the effects of different Mn contents on the thermal deformation behavior of oxidation products in the alloy. It is found that within the experimental temperature range, the higher the deformation temperature, the better the plasticity of the oxidation products. It was observed that increasing the Mn content refines the grains, enhances the deformation ability of the oxidation products, and improves the flatness of the interfaces. Since (Fe, Mn)O has a similar crystal structure to FeO, the addition of Mn refines the grains of (Fe, Mn)O, causing the deformation to be distributed across more grains under the same deformation amount, and thereby improving its plasticity. At the interface between Fe-Mn alloy oxidation products and the matrix, there exists a spinel-phase solid solution, which can deform together with the oxidation products and the matrix at high temperatures. It was found that with increasing the Mn content, the size and number of pores between the spinel phases increased. First-principles simulation calculations were used to verify this, showing that Mn promotes the generation of vacancies. The greater number of pores in the spinel phase can effectively relieve the compressive stress caused by rolling deformation, thereby improving the deformation capability of the oxidation products at the interface.
The fabrication of 304L stainless welding wires with a diameter 1.6 mm by using electrochemical cold drawing (ECD) of bars with a diameter of 5.6 mm was investigated, as well as that via traditional cold drawing (TCD) for comparison. The results indicated that the dilute H2SO4 aqueous solution was an appropriate electrolyte for ECD, and increasing the H2SO4 concentration and current density within a range improved the corrosion rate and uniformity, leading to an easier and more coordinated deformation through uniformly distributing geometrically necessary dislocations and curved large-angle grain boundaries, and decreasing their density, and thus, an enhanced electrochemical plasticization (EP). Under the optimized electrochemical parameters (0.5 mol L-1 H2SO4 electrolyte and current density of 12.2 mA cm-2), the average cumulative reduction rate required for annealing was up to ~ 34%, obviously higher than ~ 20% of TCD due to the decreased work-hardening from the EP, so that the number of annealing was significantly reduced from 10 of TCD to 5, when the drawing pass was 23. In addition, the surface of the ECD wire was distinctly smoother and brighter than that of the TCD one. These findings confirm the large potential in engineering applications of the ECD technology based on the EP effect.
To address the kinetic constraints inherent in the catalytic combustion of pulverized coal injection under low heating-rate conditions within conventional air atmospheres, a drop tube furnace was utilized to simulate the catalytic combustion of pulverized coal (PC). The effects of gas composition, oxygen concentration, the type, and the content of catalysts on the combustion reactivity were systematically analyzed. Furthermore, the structural changes of unburned pulverized coal were also examined. Experimental results indicate that as the oxygen concentration increased from 21% to 79%, compared with the O2/N2 condition, the increment in the burnout rate of PC under the O2/CO2 condition increased from 3% to 23%. After the addition of catalysts, including hematite, metallurgical oil sludge, and light-burnt dolomite (LBD), under the condition of 21% oxygen concentration, the effects of the three catalysts under the O2/CO2 condition were superior to those under the O2/N2 condition. This trend was reversed under the conditions of 38% and 79% oxygen concentrations. In all atmospheres, the three catalysts can enhance the burnout rate of PC. Among them, LBD exhibits the most favorable effect, and there exists an optimal dosage. Mechanistic analysis through scanning electron microscopy, X-ray diffraction, and N2 adsorption-desorption reveals that under 21% O2/79% CO2 conditions, high-concentration CO2 leads to the formation of pores, and additives accelerate the oxidation of C and the gasification of CO2 through oxygen transfer, thereby enhancing the burnout rate of PC.
In recent years, an increase in the content of Zn, the impurity element, in ironmaking raw materials has led to the deterioration of iron-bearing resources and has introduced new challenges to sintering dezincification. A thorough understanding of the reaction behavior of Zn during the sintering process can form a theoretical foundation for the development of efficient dezincification technology. Therefore, the reaction behavior of Zn was investigated under different temperatures and atmospheres using thermodynamic calculations and experimental simulations, and the phase transformation of Zn in each pre-reductive sintering zone was investigated. The results showed that Zn-containing materials were mainly converted into ZnO when the temperature reached 700 °C, and ZnO began to combine with Fe2O3 to form ZnFe2O4 at approximately 800 °C. At low CO concentration, ZnFe2O4 was stable, while ZnO combined with iron oxide to form Fe0.85-xZnxO in a strong reduction atmosphere. ZnFe2O4 could also be converted into Fe0.85-xZnxO and FeO. A part of Zn was converted to elemental Zn, which was volatilized and removed into the gas phase above 1000 °C. Therefore, the feasibility of dezincification via pre-reductive sintering was confirmed. At the coke ratio of 18.0 wt.% of the sintering material, the Zn removal rate reached 62.3 wt.%.
Austenitic steel is a prime candidate for structural applications in extreme environments such as nuclear fusion reactors due to its favorable cryogenic mechanical properties. A heterogeneous microstructure was developed via cold rolling followed by short-term annealing, resulting in partially recrystallized regions interspersed with non-recrystallized regions in an austenitic stainless steel. A series of tensile tests conducted at both room temperature and 77 K, combined with digital image correlation, nanoindentation, electron backscatter diffraction, and transmission electron microscopy, were employed to investigate the strain partitioning and deformation mechanisms of the microstructure. The results reveal that at 77 K, the yield strength reaches 1330 MPa and the total elongation increases to 51.49%, surpassing the performance observed at the room temperature. The cryogenic environment reduces the stacking fault energy, thereby promoting the formation of stacking faults and deformation twins in the recrystallized regions. Concurrently, the non-recrystallized regions exhibit pronounced strain-induced martensitic transformation that enhances ductility through the transformation-induced plasticity effect. These synergistic interactions between the distinct microstructural regions underpin the remarkable strength-ductility balance of the steel under cryogenic conditions.
