718Plus alloy is a recently developed nickel-based superalloy which is capable of maintaining excellent strength, hot working and welding performance. It is widely used in hot-end components such as casing, blades, fasteners and turbine disks on aero-engines. The heat treatment system has great influence on the microstructure and properties of 718Plus alloy, as well as the subsequent processing of machining and application. The research status and progress of the influence of heat treatment system on the microstructure and properties of 718Plus alloy at home and abroad were reviewed. The growth rhythm and strengthening mechanism of strengthening phase γ' in 718Plus alloy were discussed. The effects of composition and structure of δ/η phase, its quantity, morphology and precipitation position on the mechanical properties of the alloy were analyzed. The necessity of process matching between material characteristics and processing process is also expected to meet the manufacturing requirements of different parts of 718Plus material.

The materials used for penetrating warhead shells require high strength and toughness. Ultrahigh strength steel with low cost and excellent toughness has become the preferred material for penetrating warhead shells. The typical steel grades, composition, properties and development history of these materials were firstly reviewed, the strengthening and toughening mechanisms of typical ultrahigh strength steels were focused on and the need for performance of the materials was explored. Then, strengthening and toughening mechanisms of low-alloy ultrahigh strength steel and secondary hardening ultrahigh strength steel, “multiphase, metastable, multiscale” microstructure and nanocomposite precipitation were introduced, and the difficulties in the development of these materials were analyzed. Finally, the development directions of high purity, high microstructure uniformity, multiphase microstructure control and low cost were discussed.

A large amount of flue gas will be produced in the production process of the converter, and the flue gas has a high temperature and a large number of dust particles. Therefore, the cooling and dust removal of the converter flue gas and the recovery of the waste heat in the high temperature flue gas of the converter are the key to environmental protection, low carbon and cost reduction and efficiency of the converter process. The treatment methods of converter flue gas were summarized. It also points out the defects of the traditional waste heat recovery and dust removal methods, introduces and analyzes the new waste heat recovery method, and proposes three technical routes of converter flue gas and product treatment application. Currently, the capability of collecting waste heat from medium and low-temperature converter flue gas is limited. Traditional OG method and LT method have problems with gas recovery quality, heat loss and poor dust removal effect and have been unable to meet the technical requirements of low-temperature converter flue gas waste heat recovery. Vaporization cooling pipeline coal injection dry waste heat recovery method and chemical molten salt energy storage method for low-temperature converter flue gas waste heat recovery provide a new technical way. According to the existing flue gas treatment process, the technical route with the low-temperature waste heat recovery of flue gas, the diversified utilization of converter gas and steam and the intelligent smelting as the core in the future was put forward, so as to make the efficient use of energy and reduce the energy consumption.

With the proposal and implementation of the strategy of “carbon peak and carbon neutralization” in China, the metallurgical industry is facing huge pressure on carbon emission reduction. Compared with traditional blast furnace-converter steelmaking, electric arc furnace (EAF) steelmaking has lower carbon emissions, which is one of the important ways of near-zero carbon emission steelmaking. Scrap, the main raw material of EAF steelmaking, contains residual harmful elements, such as copper, tin, arsenic and antimony, which have an important impact on the smooth progress of the production process and the final properties of iron and steel products. The research progress on the source, control standard, hazard mechanism, removal and mitigation methods of typical residual elements was reviewed. The solute solidification segregation of residual elements in liquid steel during solidification is easy to produce internal cracks, and the decrease of grain boundary strength due to segregation at grain boundaries will lead to poor thermo-plasticity or the second kind of temper brittleness of steel. In addition, the enrichment between steel matrix and oxide layer will also cause surface hot brittleness. The ingredient dilution method, as the main means to control the harm of residual elements in industrial production, has a high cost and cannot fundamentally solve the problem of residual elements. The addition of inhibitory elements such as boron and rare earth can form residual element compounds to float and remove or form competitive segregation to reduce the harm of residual elements.

At present, the high carbon content in magnesia carbon refractories used in steel ladles can cause the carburization of the refractories into the molten steel and result in refractories with a high thermal conductivity, leading to significant heat loss. Reducing the carbon content will significantly decrease the thermal shock resistance of the material, while changing the way the carbon source is introduced can improve the performance of the material and provide possibilities for carbon reduction. In view of the above problems, a new method was proposed to the prepare spherical magnesium-carbon composite aggregates by the pellet granulation method and replace flake graphite to improve the thermal shock resistance of the material. The results show that the mechanical properties and thermal shock resistance of the materials are improved after the introduction of the spherical magnesium-carbon composite aggregate into the magnesium-carbon refractories. The flexural strength and fracture energy of the best substitution amount of refractories after heat treatment at 1 100 ℃ and 1 550 ℃ are increased by 27.93%, 15.17% and 4.12%, 8.84%, respectively. The thermal shock resistance and residual strength are increased by 9.15% and 0.8 MPa, respectively. Moreover, the crack propagation after thermal shock showed more through aggregate fracture, mainly due to the introduction of microcracks by the addition of spherical magnesium carbon composite aggregate and the tighter bonding between the aggregate and matrix caused by the in-phase sintering of the aggregate and matrix.

Argon injection in nozzle can prevent nozzle clogging during the continuous casting process, but it can also cause defects of subcutaneous bubbles in slabs and increase the risk of intensified fluctuations at the steel-slag interface. Herein, for the process of argon injection from the bowl of nozzle, a three-dimensional mathematical model of the tundish-nozzle-mold was established by coupling the DPM model and VOF model. A 1∶2 scaled water model experiment was conducted to verify the morphology of bubble plume and size distribution of bubbles in the mold. The effects of argon flow rate, casting speed, and submerged depth of nozzle on the flow field, size distribution of bubbles in varied regions and fluctuation behavior of steel-slag interface in the mold were investigated. The results show that with a low argon flow rate, the liquid steel flowing out from the nozzle ports separates into two streams: one rushes to the narrow face, and the other impacts the steel-slag interface. Large size bubbles are mainly distributed in the near-nozzle region of the 1/2 and 1/4 wide faces. With the increase in the argon flow rate, the impacting position of the stream on the narrow face move upwards, and the slag open eyes appear in the vicinity of the nozzle and gradually become larger. Moreover, the number of large size bubbles in 1/2 wide face first increases and then decreases, and the number of small size bubbles near the narrow face increases significantly. With a low casting speed, a single-roll flow pattern is formed in the mold, and the bubbles are concentrated near the wall of the nozzle with a large slag open eye generated here. An increasing casting speed is beneficial for the uniform spatial distribution of bubbles in the mold, and reduce the area of slag open eye, but will increase the number of small bubbles in the area near the narrow face. In addition, a low submerged depth is favorable for bubbles to float upwards in the near-nozzle region. Moderately increasing the submerged depth of the nozzle can decrease the number of small bubbles near the wide face.

The flue gas waste heat at the fourth stage exit of annular cooler equipped with 360 m² sintering machine was taken as the research object, and the circulating water heated through the flue gas heat exchanger was selected as the heat source of organic Rankine cycle (ORC) system. The thermal and economic models of system were established firstly, and the effects of ORC thermodynamic parameters on the system thermal performance and economic performance under different working mediums were investigated. Furthermore, a multi-objective optimization method based on the genetic algorithm was adopted to determine the optimal cycle working medium of ORC system, as well as the best thermal performance and economic performance. The results indicate that, the smaller the superheat degree and pinch-point temperature difference in evaporator are, and the higher the evaporation temperature is, the larger the system exergy efficiency is. The system electricity production cost gradually reduces with rising the evaporation temperature, and reduces first and then rises with rising the superheat degree and pinch-point temperature difference in evaporator. When the system thermal parameters are optimum, the system exergy efficiency and electricity production cost of R245fa are better than those of R600a and R236ea, so it should be preferentially selected as the circulating working medium of ORC system driven by the low temperature sinter flue gas waste heat. At this time, the maximum exergy efficiency of ORC system is 46.34%, and the minimum electricity production cost is 0.121 23 $/(kW·h).

Changes in the morphology and size of the γ′ phase of C-HRA-3 heat-resistant alloy after aging at 700 and 750 ℃ with respect to aging temperature and time were investigated. The coarsening kinetics of γ′ phase is derived, and an attempt is made to predict the γ′ phase size at 10⁵ h. The results show that the shape of γ′ phase is uniform spherical distribution after long term aging at 700 ℃/11 023 h in the C-HRA-3 alloy. The size of the γ′ phase increases and the shape changes from spherical to partially spherical after long term aging at 750 ℃/11 023 h. The size of the γ′ phase gradually increases with the increase in aging temperature and time, and the effect of aging temperature is more significant. The growth kinetics equation of the γ′ phase in C-HRA-3 alloy after aging at 700 and 750 ℃ was obtained, and the effective activation energy of γ′ phase growth, D_Eff, was calculated to be 260 kJ/mol. It was predicted that the average diameter of the γ′ phase would be about 140 nm and about 230 nm when aged at 700 and 750 ℃ for 10⁵ h, respectively.

As an essential fundamental material in high-temperature industries such as metallurgy and building materials, refractories inevitably endure chemical corrosion and mechanical fracture (collectively referred to as "damage") under coupled thermal-chemical-mechanical conditions during the period of service, resulting in the deterioration and wear of high-temperature furnace linings and affecting quality of the products. Conducting postmortem testing analysis methods to evaluate damage behavior presents challenges, as direct observation of the in-situ degradation process of refractories within high-temperature and complex environments is not feasible. The paucity of process information, particularly regarding the condition of thermal-chemical-mechanical coupling, can potentially skew the analysis outcomes. The research progress in the application of machine vision/hearing technologies in characterizing and evaluating the damage behavior of refractories was reviewed. It indicates that the application of digital image correlation (DIC) and acoustic emission (AE) techniques, which achieve non-contact real-time monitoring of the full-field strain and acoustic emission signals of refractories, can characterize the degradation evolution process under multi-factor coupling conditions. These techniques provide a novel approach for accurately revealing the damage mechanisms and evaluating the service performance of refractories. This research aims to provide theoretical support for the development of superior refractories for high-quality product smelting and production.

Soft magnetic material is one of the key energy materials to realize the technological breakthrough in the important industries upstream of electronic components. The advancement and investigation of high-performance soft magnetic materials are paramount for energy conservation, consumption reduction, and the successful execution of the "Made in China 2025" initiative. High-entropy alloys have a wide range of adjustable magnetic properties due to the doping of magnetic elements such as Fe, Co and Ni. Therefore, high-entropy alloys are poised to emerge as superior soft magnetic materials. This review delineates the pivotal factors influencing the magnetic properties of high-entropy alloys, highlighting the magnetic properties of high-entropy soft magnetic alloys are very sensitive to the chemical composition, preparation process and parameters, and the phase structure. Heat treatment is identified as the primary strategy for refining microstructures of high-entropy alloys and optimize their properties. In addition, the intrinsic mechanism that affects the magnetic characteristics of high-entropy soft magnetic alloys is elucidated from the atomic scale based on the theoretical simulation method, which further defines the dependence relationship between the magnetic properties of high-entropy soft magnetic alloys and the magnetic domains. Finally, it condenses part of the scientific problems in the development of high-entropy soft magnetic alloys and briefly summarizes the directions that should be focused on in the future development of high-entropy soft magnetic alloys.

A large amount of industrial solid waste containing high aluminum-silicon content was generated in China every year, which was expected to become the raw material for the preparation of lightweight refractories in the metallurgical industry. The research status of industrial solid waste such as tailings, metallurgical slag, dust sludge, fly ash, and coal gangue in the preparation of lightweight aggregates was summarized. The performance advantages of preparing lightweight refractories by using artificial aggregates instead of natural aggregates were compared and summarized. The relevant research on the microporosity of lightweight aggregates and the homogenization of the matrix in the preparation of lightweight refractories was summarized, clarifying the rationality and development prospects of using industrial solid waste aggregates to prepare lightweight refractories. The need for developing new processes and technologies for preparing lightweight refractories from solid waste aggregates, as well as continuously improving the thermal insulation performance and slag resistance of aluminum-silicon lightweight refractories, was proposed to achieve efficient utilization of industrial solid waste resources and the lightweight and functional development of high-performance refractories in metallurgy.

The effects of Mn content and solution treatment temperature on the microstructural evolution and mechanical properties of 17Cr-2Ni-0.2N-xMn duplex stainless steel were investigated by utilizing microstructural characterization and mechanical testing methods. The results indicate that while Mn, among the austenite-forming elements (Mn, Ni, N), exerts the least influence on the austenite-ferrite phase equilibrium temperature, it significantly enhances austenite stability. An increase in Mn content decreases the amount of quenched martensite and suppresses deformation-induced martensitic transformation, thereby improving the steel′s ductility and toughness. Notably, with an Mn mass fraction of 3%, the steel attains a desirable balance of mechanical properties, including 35.5% elongation, 944 MPa tensile strength, and 139 J impact energy at room temperature. Furthermore, an appropriate alloy composition enables the formation of a nearly equiaxed dual-phase microstructure in the 17Cr type duplex stainless steel after high-temperature solution treatment. The studied 17Cr-type duplex stainless steel exhibits excellent overall mechanical properties, with a maximum tensile strength exceeding 1 200 MPa in the solution-treated state, elongation after fracture greater than 50%, an impact toughness of 204 J at room temperature, and 99 J at -10 ℃.

Rotary hearth furnace process is one of the main processes for treating zinc-containing dust in iron and steel works. The passivation technology of metallized pellets with zinc dust was studied in view of the problems that zinc-containing dust metallized pellets produced by rotary hearth furnace are easy to heat and spontaneous combustion during stacking, which seriously affect the storage, transportation and use of products. The results show that during the cooling and storage of metal pellets, the highly active sponge iron reacts with water to produce hydrogen. Meanwhile, one main reason for autoignition and calorification of metallized pellets is that the galvanic battery reaction occurs to generate the hydrogen, and much heat releases from oxidation of metallized iron within pellets. Compared with natural passivation, spraying CaCl₂, lime water and other solutions, the use of MgCl₂ solution (5 wt.%) to spray zinc dust metallized pellets, cooling and passivation, has a better effect. After storage of the treated metal pellets for 360 h, oxidation weight gain rate is only 1.42%, the metallization rate of pellets decreased by less than 12%. The expanded experiment proves the feasibility of the passivation technology in actual production, which provides a new solution for the safe storage of zinc-containing dust metallized pellets produced by the rotating hearth furnace process.

With the soaring prices of Ni and Mo, it is necessary to develop new high-performance and Ni- and Mo-saving stainless steel. Based on the composition of the S32654, a new type of super austenitic stainless steel (SASS) with 24.5% Cr-17% Ni-5% Mn-6.3% Mo-0.7% N was prepared by pressure metallurgy and element synergistic control methods. The precipitation behavior and mechanical properties of the steel were studied. The results indicate that during isothermal aging at 800-1 050 ℃, as the temperature increased, the cellar precipitates composed of Cr₂N and σ phases first increased and then decreased, and 900 ℃ was confirmed to be the precipitation nose temperature of the steel. The ultimate tensile strength (UTS), yield strength (YS) and elongation of solid solution sample (1 200 ℃-30 min) can reach 958 MPa, 517 MPa and 77.4%. With the prolongation of aging time at 900 ℃, the cellular precipitates underwent nucleation and growth, which promoted intergranular cracking, resulting in a decrease in UTS and elongation (797 MPa and 13%, respectively, after aging for 120 min), and the yield strength (YS) first decreased and then increased. After 5 min of aging, the formation of intergranular precipitates consumed solid solution strengthening elements such as Cr, Mo, and N, leading to the reduction of YS to 492 MPa. After aging for 30 min and longer, the number and size of cellular precipitates increased, leading to an increase in YS (535 MPa, after aging for 120 min).

Refractories, as the high-temperature furnace lining for the smelting of iron and steel, play a crucial role in improving thermal efficiency and reducing energy consumption in the industry. In recent years, the research on lightweight refractories for the smelting of advanced steel has been paid extensive attention. Thus, the research progress of lightweight refractories for the smelting of advanced steel based on the types of lightweight refractories were reviewed, in order to guide the design and development of long-lived lightweight refractories and promote the energy conservation and emission reduction in high-temperature furnaces for the smelting of advanced steel. The lightweight of refractories can be achieved by the introduction of lightweight aggregates or the design of a density gradient structure. Lightweight refractories have low thermal conductivity and bulk density and good thermal insulation properties, which can be directly used as working linings. The preparation technology, types, and damage mechanism of lightweight refractories still need to be further studied.

High-entropy alloys (HEAs) demonstrate exceptional resistance to hydrogen embrittlement due to complex chemical composition, disordered atomic structure, severe lattice distortion effect and so on. These factors result in distinct hydrogen solubility, hydrogen diffusion coefficients, and hydrogen trapping ability compared to other metallic materials. In order to accelerate the development of HEAs in the field of hydrogen embrittlement resistance, it reviews the existing studies, summarizes the influence and mechanisms of microstructure, alloying elements, sources of hydrogen and preparation parameters on the resistance to hydrogen embrittlement of HEAs, and finds that there is a specific range of influence for the aforementioned factors on the resistance to hydrogen embrittlement of HEAs, and this specific range needs further experimental research and theoretical analysis to determine for different HEAs. Finally, some design strategies are introduced to enhance the resistance to hydrogen embrittlement of HEAs, such as grain boundary engineering, gradient nano-twins, introducing nano-carbide/nitride, computer aided design, and the focus of future research work of resistance to hydrogen embrittlement of HEAs is prospected.

The development of high-pressure hydrogen storage materials has become a key goal in promoting China's hydrogen energy construction. With good hydrogen embrittlement resistance, formability, and low-temperature toughness, austenitic stainless steel (ASS) is considered to be an excellent candidate material for high-pressure hydrogen storage containers. However, the excessive use of precious metals in traditional ASS makes it unsuitable for large-scale application, and the low strength of ASS can also cause safety hazards. Therefore, thermodynamic phase diagram calculation methods are used to design an ASS (named NEASS), and slow tensile testing and various microscopic characterization methods are used to evaluate its hydrogen embrittlement resistance. The results show that the strength and hydrogen embrittlement resistance of NEASS are about 15% and 70% higher than those of 316L stainless steel, respectively. During the deformation process after hydrogen charging, NEASS exhibits a special multidirectional slip mechanism, which alleviates local stress concentration and effectively inhibits the initiation and failure of hydrogen-induced cracks.

In the demand for a balance between high strength and high ductility of martensitic steel for automotive application, a new rapid tempering process was proposed. The research involved rapid tempering of newly designed medium-carbon martensitic automotive steel and comparison with that by conventional tempering approach to explore the impact on the steel′s microstructure and properties. Employing the techniques and equipment such as tensile testing machines, digital image correlation methods, X-ray diffraction, electron backscatter diffraction, and field emission scanning electron microscopy, the study revealed that the rapidly tempered specimen maintained high dislocation density and refined precipitated carbides, thereby preserving the martensite′s high strength. The results showed that the new processing successfully enhanced the material′s tensile strength and yield strength to 1 616 and 1 466 MPa, respectively, at a rapid tempering temperature of 400 ℃, leading to an increase of 10.2% and 12.5% over the conventional process while maintaining an elongation of over 10%. When tempered at 300 ℃, the martensitic automotive steel maintained a high elongation with a tensile strength near 2 000 MPa. These findings not only offer a new perspective on the preparation of high-strength martensitic automotive steel but also serve as a significant reference for material selection in future automotive industries.

To establish the relationship between composition, heat treatment process, and creep performance of austenitic heat-resistant steels with 18%-25%Cr under various temperature and stress service conditions, the chemical composition, heat treatment process, creep test rupture time, and creep test temperature of nine types of austenitic heat-resistant steels were used as input parameters, with creep strength as the output parameter. Using SHAP values and maximum marginal correlation to select features, a prediction model for the creep performance of 18%-25%Cr austenitic heat-resistant steel based on a BP neural network was established. The results indicate that when compared to traditional methods, this model can construct the relationship between the composition, heat treatment process, and creep rupture properties of 18%-25%Cr austenitic heat-resistant steels under complex service conditions, achieving accurate prediction of creep rupture property for 18%-25% Cr steels. For specific steels, the combination of the BP neural network model and thermodynamic calculation methods can further screen and optimize the composition combination of the steel from the perspective of structure-property.

The utilization of relatively inexpensive and abundant hematite-limonite is of great practical significance for expanding the raw material source of pellets and promoting the green transformation of the iron and steel industry. For an imported hematite-limonite (AM), its wet milling-settling-filtering characteristics were investigated, and at the same time, laboratory trials and on-site industrial experiments were conducted on the roasting behavior, metallurgical performance and microstructural characteristics of pellets under simulated grate-rotary kiln process conditions, revealing the influence of the addition of AM on the raw material pre-treatment and pellet production. The results show that AM is an easy-to-grind ore, which is difficult to be settled and filtered after wet milling due to the presence of limonite, and it can be used with hard iron ore to strengthen the settlement and filtration performance in the actual production; when the milling fineness of AM(-0.074 mm content) is controlled at 70 mass%-80 mass%, and the specific surface area of the mixed concentrates is 1 500 cm²/g, qualified pellets(CCS≥2 500 N/pellet, RI＞60%, RDI_+3.15＞97% and RSI＜20%) can be prepared with AM ratios ranging from 0 to 40 mass%. However, with the increase of AM ratio from 0 to 40 mass%, the suitable preheating and roasting temperatures of pellets need to be increased by 50 ℃, respectively. The on-site industrial experiments further verified the laboratory results, under the condition that the thermal system of grate-rotary kiln pelletizing process is basically stable, the AM ratio should be controlled within 17 mass% to obtain good technical and economic indexes, and the energy consumption of the process will tend to increase if the AM ratio continues to be increased.

To study the thermodynamic equilibrium of the key elements Al and Ti of the 06Cr18Ni11Ti austenitic stainless steel during the electroslag remelting process, a thermodynamic model based on the ion and molecule coexistence theory (IMCT) was established. For the four-component slag (Al₂O₃-CaO-MgO-CaF₂) with no TiO₂, an IMCT formula was developed to calculate the effects of the components of the slag system and the initial Al content in the steel on the equilibrium of Al and Ti. The results indicate that excessive Al₂O₃ can cause the burning loss of Ti element, excessive CaO will lead to the burning loss of Al element. CaF₂ and MgO in slag, which can be used to adjust the viscosity, melting point, and specific resistance of the slag system, have little impact on the equilibrium of Al and Ti. With the increase in temperature in slag, the content of Al at equilibrium time rises, while the content of Ti drops. When more initial Al content is in steel, the content of Al and Ti in equilibrium state is higher.

The mechanism model of converter smelting has developed rapidly, but there are still many problems, such as the disconnection between model parameters and actual blowing and feeding conditions, and the inconsistency between predicted results and actual situations. The establishment of metallurgical models based on mechanism analysis methods such as multiple reaction zones in the converter melt, minimum Gibbs free energy theory, thermodynamic and kinetic coupling reactions has gradually become a consensus in the industry. Changes in the composition of molten steel and slag during the converter melt reaction process were studied and demonstrated the common issues of metallurgical laws in the smelting process. The analysis of the important characteristics of the molten pool reaction was also conducted. Moreover, the mechanism of synchronous changes in FeO accumulation and consumption during the smelting process, the equilibrium state of the reaction interface layer, and the slag-forming route of slag material in the smelting process were proposed. Based on the theory of multiple reaction zones in the converter, the molten pool was divided into“gas-steel liquid” jet impact zone,“slag-metal droplets-furnace gas” emulsification zone, and“slag-steel liquid (metal droplets)” slag zone. An oxygen allocation model for dynamic regulation of three reaction regions with values ranging from 10%~20%: 45%~65%: 40%~25% was established. Application of the model based on the mixing and stirring of the melt pool in the three reaction zones of the converter showed that when the comprehensive stirring energy was in the range of 0.60~0.75, the variation range of the equivalent mass transfer coefficient at the reaction interface was 1.019~1.024.

Sintering is an indispensable link in the whole iron and steel industry production, the change of parameters in the sintering process will directly affect the quality and output of sinter. Taking the 150 m² sintering machine of a steel plant as the research object, the simulation software Fluent was used to simulate the sintering process parameters. By establishing a suitable physical and mathematical model, and based on on-site actual data, the temperature field changes in the material layer were simulated. Single factor analysis was used to study the effects of carbon content, porosity, material layer thickness, and suction negative pressure on timerequired to reach the sintering end point, and the optimal process parameters were determined. The research results show that increasing the carbon content shortens time required to reach the sintering end point, and the optimal sintering end point position is achieved when the carbon content is 4.23 mass%. When the porosity of the layer increases,time required to reach the sintering end point becomes shorter, and the sintering end point position is the best when the porosity is about 0.49. When the thickness of the material layer increased,time required to reach the sintering end point is extended. When the thickness of the material layer reaches 734.13 mm, the maximum vertical sintering speed reaches 0.321 mm/s.By increasing the suction negative pressure,time required to reach the sintering end point will be shortened. When the suction negative pressure reaches 15 kPa, the vertical sintering speed is optimal. Under the optimized process parameters, the quality and output of sintered ore are improved.

The effects of roasting temperature and basicity of pellets on compression strength of pellets were investigated by roasting experiments using horizontal tube furnace. The effect of pellets basicity, including natural basicity, 0.4, 0.6, 0.8, and 1.0, on the mineral composition of pellets were analyzed by using SEM-EDS techniques. The possible generators of Fe₂O₃-SiO₂-CaO system were calculated using FactSage software, and the above experimental results were analyzed and verified in combination with phase diagrams. The results show that for the pellets with basicity of 0.3-1.2, the compressive strength showes an obvious increasing trend with the increase of basicity, and a small amount of calcium-containing silicate minerals are firstly generated during the roasting of low-basicity pellet, and then calcium silicate minerals and calcium ferrate-based minerals are further generated during the roasting as the pellets basicity increased.

The rapid dissolution of lime in molten slag to improve the slag basicity contributes to the efficient dephosphorization and energy saving during steelmaking. The comparative study on the dissolution and dephosphorization behavior of lime and limestone in slag was conducted through high-temperature dissolution experiments and slag-metal reaction dephosphorization experiments. Results show that lime dissolved rapidly in the initial stage after added into molten slag, followed by a gradual decrease in dissolution rate and almost stagnation in the later stage. In the initial stage of limestone dissolution, a large amount of CO₂ generated by the decomposition of CaCO₃ hinders the contact between the slag and the surface CaO layer formed by CaCO₃ decomposition, thereby hindering the penetration of slag into the lime layer and the dissolution of lime. The CO₂ generated by later decomposition plays an important role in accelerating the dissolution of lime. There is an important correlation between the dephosphorization reaction and the rapid increase in CaO content in the slag. Due to the slow dissolution of lime in the later stage, the dephosphorization rate is lower, and the phosphorus content in the liquid metal is relatively higher. During the dissolution of limestone for dephosphorization, the CaO content in the slag increases more slowly than lime due to slow dissolution in the early stage, which leads to a slightly slower mass transfer coefficient of dephosphorization reaction in the early stage compared with the test of lime. In the later stage, because of the accelerated dissolution of limestone, the mass transfer coefficient in the dephosphorization reaction increases by about 11.6 times compared with that in the early stage and about 6.6 times higher than that in the test of lime.

The turbine blades made of superalloy are among the most critical components in the hot section of aero-engines and gas turbines. Operating within a complex environment of high temperatures, stress, and gas corrosion over extended periods, they are susceptible to various forms of damage. Turbine blades made of superalloy is costly, so it is not economical to replace blades with only minor damage. Therefore, research on the turbine blades damage and repair technology is crucial for reducing the overall repair and manufacturing cost associated with superalloy turbine blades. The necessity for researching turbine blade damage and repair technology was firstly clarified. Then, the main types of service damage experienced by superalloy turbine blades were classified, including internal metallurgical microstructure damage and apparent damage. Various repair technologies were summarized, including welding repair technology, damage repair technology based on additive manufacturing, and recovery heat treatment technologies while analyzing their respective advantages, disadvantages and applicability. Finally, it provides an outlook on the future development direction of superalloy turbine blade repair technologies.

The corrosion resistance of Ti-Mo microalloyed steel was evaluated using the cyclic immersion corrosion testing machine and electrochemical workstation. The experiments combined the results from the optical microscope, X-ray diffractometer, scanning electron microscope, and atomic force microscope to discuss the influence factors of microstructure type on corrosion resistance. The results show that with the decrease of the proportion of pearlite and bainite in the investigated steel, the growth rate of the rust layer slows down, the proportion of the inner rust layer increases, the compactness of the rust layer and the bonding ability with the iron matrix are improved, and the corrosion weight loss rate decreases. At the same time, the self-corrosion current density of bare steel decreases, the charge transfer resistance increases, and the corrosion resistance improves. The microstructure potential of the investigated steel was measured, and the ferrite potential was higher than that of bainite and pearlite.As a microscopic corrosion cell was formed between the structures, the galvanic corrosion strength is the main factor affecting the corrosion rate. That is to say, reducing the volume fraction of bainite/pearlite in Ti-Mo high strength steel can improve microstructure uniformity, suppress galvanic corrosion, and enhance corrosion resistance.

The incorporation of high-magnesium boron-bearing magnetite concentrate in pellet production facilitates the efficient separation of boron and iron within the concentrate. However, the limited research has been conducted on the influence of the ratio of high-magnesium boron-bearing magnetite concentrate on the pellet consolidation mechanism and reduction characteristics. The effects and mechanisms of varying the ratio of high-magnesium boron-bearing magnetite concentrate on the strength and reducibility of the pellets were investigated. Additionally, it explores the potential for enhancing reduction characteristics by lowering the firing temperature during pellet preparation based on the consolidation mechanism of the pellets. The results indicate that the increase in the proportion of high magnesium boron magnetite concentrate in ordinary magnetite concentrates helps to increase the content of spinel type magnesium ferrite phase inside the pellets, improve the grain morphology of hematite, promote the formation of "hematite spinel type magnesium ferrite" structure, and thus improve the strength of the pellets. However, during the preparation of pellets with the addition of high-magnesium boron-bearing magnetite concentrate, the spinel-type magnesium ferrite generated during the firing process can have a significant negative impact on the reducibility of the pellets. Therefore, to ensure both the strength of the pellets and a certain level of reducibility, the firing temperature of pellets containing high-magnesium boron-bearing magnetite concentrate should not exceed 1 150 ℃.

It was studied that the effects of solution temperature on heat-treated microstructure and resultant mechanical properties of a novel nickel based superalloy with a high content of γ′ precipitates by means of optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and mechanical experiments. The as-received hot-rolled microstructure undergoes static recrystallization during the solid-solution treatment completely. The recrystallized grains remain fine uniformly at 1 120 and 1 130 ℃, but become significantly coarser with a poor uniformity at 1 150 and 1 190 ℃. As the solid-solution temperature rises, the content of primary γ′ precipitates at grain boundaries decreases; while the number of secondary γ′ precipitates increases and their size decreases, until it exceeds the γ′ solvus (about 1 134.3 ℃). It is indicated that the mechanical properties of this alloy are jointly determined by the size of γ grains and the content and distribution of γ′ precipitates within γ grains. The tensile strength both at room temperature and 850 ℃ increases first and then decreases with the increase of solid-solution temperature. Compared with that of coarse-grained microstructure, the tensile plasticity of fine-microstructure is high at room temperature but poor at 850 ℃. The coarser the recrystallized γ grains, the longer the stress-rupture lifetime and the higher the stress-rupture plasticity under 850 ℃/350 MPa. The heat-treated microstructure with a solid-solution temperature of 1 130 ℃ obtains a higher high-cycle fatigue lifetime at 850 ℃.

The fatigue limits and S-N curves at 25, 200, and 315 ℃ were measured by using the QBWP-10000 cantilever rotary bending fatigue testing machine. The slow, stable, and fast crack propagation rate curves at different temperatures were tested using a universal testing machine. Based on the fact that fatigue cracks in M50 bearing steel mainly originate from carbides in the steel, a local damage life model related to temperature and time was established by combining the temperature dependent variation of parameters such as elastic modulus and Poisson's ratio with the hardening effect caused by cyclic stress at the carbide interface. Research has found that the stress intensity factor of fatigue defects such as carbides in M50 bearing steel is the amount of fatigue damage; the increase in temperature shortened the crack initiation time and accelerated the crack propagation rate, thereby reducing the fatigue ultimate strength of M50 bearing steel; the main factors affecting the initiation life are the number of cycles, temperature, fatigue defects, and local hardening of carbide interfaces caused by applied cyclic stress.

High pressure roller grinding (HPRG) pretreatment can improve the quality of pellets, but its mechanical activation effect is affected by many parameters. The effects of HPRG pretreatment on the properties, pelletizing and roasting properties of vanadium-titanium-iron concentrate under different water contents were studied, and the suitable wetting degree for mechanical activation of vanadium-titanium-iron concentrate by HPRG pretreatment was determined. The results show that when the water content increases from 5.5 wt.% to 8.5 wt.%, the particle size of vanadium-titanium-iron concentrate decreases firstly and then tends to be stable after HPRG pretreatment, the specific surface area increases, and the hydrophilicity and billability are enhanced. However, the increase of water content is not conducive to the dissociation between iron ore and gangue, and the mineral liberation degree of titanomagnetite decreases. When the water content is 6.5 wt.%-7.5 wt.%, the mechanical activation of HPRG is the strongest. At this time, the grain size of titanomagnetite is the smallest, the lattice distortion rate is the largest, and the quality index of the prepared vanadium-titanium-iron concentrate pellets is the best. The suitable water content of vanadium-titanium-iron concentrate in HPRG pretreatment is 6.5 wt.%-7.5 wt.%. Correspondingly, the vanadium-titanium-iron concentrate needs to be wetted to a capillary water content of 4.4 wt.%-5.4 wt.% before HPRG pretreatment.

With the continuous promotion of the national“dual carbon” target, while developing emerging technologies in iron and steel industry, fuel diversification and resource efficiency are also the only way to achieve energy conservation and emission reduction. To explore the potential application of printer waste toner in the iron and steel industry, to explore the feasibility of the blast furnace injection process, the combustion behavior, performance, synergistic effects, and dynamic parameters of waste toner, pulverized coal used in blast furnace injection, and their mixed fuel in different proportions were investigated by thermogravimetric analysis to understand the fuel combustion mechanism and provide a theoretical basis for the injection of new fuels into blast furnaces. The results show that waste toner has excellent combustion performance, and its comprehensive combustion characteristic index, combustion stability, and flammability index are all better than those of pulverized coal. This suggests that waste toner can serve as an auxiliary fuel for blast furnace injection, potentially replacing a portion of pulverized coal. When the blending ratio of waste toner is 10%, the combustion performance of the mixed fuel is optimal, with a comprehensive combustion performance index, combustion stability, and flammability index of 21.97×10^-10 (min^-2·K^-3), 23.33×10^-6 (min^-1·K^-2) and 25.16×10^-6 (min^-1·K^-2), respectively. Through analysis of the ash content of waste toner, it was found that the mass fraction of Fe₃O₄ in the ash content of waste toner was as high as 84.99 mass%. Through the analysis of the synergistic effect between waste toner and pulverized coal, it was found that the blending of wastetoner and pulverized coal can promote combustion, and the synergistic effect parameter F is in the range of 0.80-1.15. Through dynamic analysis, it was found that the activation energy required for combustion of mixed fuels is lower than that of single fuels, and it generally decreases with the increase of the proportion of waste toner.

Iron coke is one of the main potential technologies for low-carbon ironmaking in blast furnaces. Evolution characteristics of the tensile strength, mechanical strength, and thermal properties of iron coke under different raw material ratios were analyzed. The mechanism of the influence of raw material ratios on the microstructure, pore structure, and carbon crystal structure of iron coke was analyzed using characterization methods such as optical microscope, SEM-EDS, BET, and XRD. The research results indicate that a lower porosity and a more uniform pore structure in iron coke contribute to enhancing its tensile strength. When the iron ore powder content exceeds 10 mass%, there is a significant decrease in the mechanical strength of the iron coke. Taking into account the mechanical strength and thermal performance of iron coke, the mass fraction of iron ore powder added should not exceed 15 mass%. By adjusting the addition of 1/3 coking coal to optimize the metallurgical performance of the iron coke, it is found that when the addition is between 20 mass%-22 mass%, the mechanical strength of the iron coke reaches the level of second-grade coke. The reactivity of iron coke exhibits a trend of initially decreasing and then increasing with the increasing in 1/3 coking coal content, and the underlying reason is the change in carbon structure and micropore structure.

In order to investigateonerosion of stainless steel AOD high silicon smelting process on MgO-CaO bricks, theobservation, chemical analysis and XRD analysis on stainless steel AOD slag in desilication period,the appearance of the used and unused MgO-CaO bricks, combined with microstructural analysis and thermodynamic calculations were studied. It was found that stainless steel AOD slag in desilication period produced by the AOD high silicon smelting process is glassy phase with basicity of 1.02. The effect of tricalcium silicate on MgO-CaO bricks is less than that of dicalcium silicate. Stainless steel AOD slag in desilication period can produce dicalcium silicate;stainless steel AOD slag in reduction period can produce tricalcium silicate;and stainless steel AOD slag in desilication period is more erosive than stainless steel AOD slag in reduction period to MgO-CaO bricks. When the refractories mass fraction is 100%, the erosion content of stainless steel AOD slag in desilication period is 53.8%, and the resulting slag mass fraction is 36.7%.The erosion content of stainless steel AOD slag in reduction period without stainless steel AOD slag in desilication period is 35.1%, and the resulting slag mass fraction is 25.0%. When refractory materials react with stainless steel AOD high silicon slag and then react with stainless steel AOD reduction slag, the corrosion mass fraction of stainless steel AOD reduction slag is 46.2%, and the slag mass fraction produced is 87.8%. Therefore, the double slag smelting caused by high silicon smelting process has the greatest impact on magnesia calcium bricks.

The difference of carbides in Fe-Mo-Cr-C alloy steels in terms of number, size and composition by different spheroidal annealing holding time was systematically investigated using scanning electron microscopy (SEM). The results show that the higher hardness of the specimens with longer annealing time is due to the dissolution of more eutectic carbides during austenitization and the precipitation of a greater number of secondary carbides of the M₆C (Fe₃Mo₃C) type with smaller sizes. The first-principle calculations show that Fe₃Mo₃C has the best overall performance, which is conducive to the improvement of the overall mechanical properties of the steel among the carbides of Fe-Mo-Cr-C alloy steels in the annealed condition. Different high and low energy levels and differences in orbital hybridization of Fe-d, Mo-d, C-d and C-p are responsible for the superiority of Fe₃Mo₃C over Fe₂Mo₄C, which is also a M₆C-type carbide, both in terms of structural stability and mechanical properties. The effect of carbides on mechanical properties of steel in spheroidal annealing was studied, which can provide a theoretical basis for other mold steel materials in the heat treatment process technology.

The color and texture of the flame at the converter mouth are closely related to the carbon content and temperature of the converter. The prediction of the carbon content and temperature of the converter through the flame characteristics of the converter mouth collected by the spectrometer provides a new idea for the end point control of converter steelmaking. Based on the flame spectrum data set of the converter mouth and the PSO-ELM neural network, a prediction model of the carbon content and temperature of the converter is established. In view of the fact that the original spectrum contains more noise, stray light, etc., wavelet algorithm is used to reduce the noise of the spectral data set. Due to the large amount of flame spectrum data at the converter mouth and the large amount of redundant information, the attribute reduction algorithm of the Skowron difference matrix is used to find the smallest data set with the smallest decision set coverage from the given 2 048-dimensional wavelength data, and 8 special diagnosis indicators are obtained. By calculating the MIC coefficients of the 8 indicators, it is proved that the selected indicators are independent and non-collinear, avoiding the risk of unstable modeling and overfitting due to the high correlation among the indicators. A prediction model is established based on the PSO-ELM neural network, and the particle swarm optimization algorithm is used to optimize the defects of the input weights and hidden layer thresholds randomly generated by the ELM during initialization. By applying the PSO-ELM model to the prediction of carbon temperature of converter, the example validation shows that the model has high accuracy and good prediction effect on carbon temperature prediction, which is suitable for the prediction of carbon temperature of converter and has a better engineering application prospect.

To study the microstructure evolution and indentation behavior of aluminum alloy, AA6063 aluminum alloy plate was prepared by cold rolling method at room temperature. The microstructure and local mechanical properties of AA6063 aluminum alloy plate were analyzed by metallography opticalmicroscopy, scanning electron microscopy and microindentation. The results show that the grains of AA6061 aluminum alloy are elongated along the rolling direction and the work hardening is obvious after rolling at room temperature. With the increase of plastic deformation, the diagonal length, maximum indentation depth and residual indentation depth decrease under the same indentation load. The Vickers hardness of AA6063 aluminum alloy increases with the increase of plastic deformation, and the relationship between the hardness and plastic strain is exponential. With the increase of rolling deformation, the dislocation density of aluminum alloy specimen increases during indentation deformation. For aluminum alloy with the same deformation, the dislocation density gradually decreases and eventually tends to a stable value with the gradual increase of the maximum indentation load. Both the Vickers hardness and dislocation density of AA6063 aluminum alloy increase with the increase of reduction in thickness. As a result, the indenter resistance increases and plastic energy dissipated decreases after plastic deformation for AA6063 aluminum alloy. Dislocation slip is the main plastic deformation motion for AA6063 aluminum alloy.

The FeCrCoMn high entropy alloy coatings were prepared on 45 steel substrates using laser cladding technology by designing a triangular powder preforms, and the effects of the solidification process on the structure and tribological properties of the coating were investigated. It is found that under the same solidification conditions, the increase in the width of the precet layer w reduces the solidification cooling rate, which results in the dissolving precipitation of the σ phase in the bi-phase FCC+HCP solid solution, and the microstructure evolves gradually from equiaxed crystals to columnar crystals and dendritic crystals, with a gradual increase in grain size. The tribological investigation shows that with the increase in the width of the pre-positioned layer, the wear is gradually serious due to the decrease of coating hardness and coarsening of the structure. However, when the width of the pre-positioned layer is 20 mm, the precipitated σ phase with higher hardness plays an anti-wear role to a certain extent, the friction coefficient and the wear rate are reduced, and the wear mechanism is dominated by abrasive wear. The results show that the solidification process is the key factors that cannot be ignored in laser cladding technology which will dominate the structure and properties of FeCrCoMn high entropy alloy coatings.

The magnetic properties of non-oriented silicon steel are greatly affected by micrometer and nano-sized sulfide. The effect mechanism of deep desulfurization of liquid steel on the inclusion characteristics and magnetic properties of the finished non-oriented silicon steels was investigated. The composition, number, and size of inclusions and precipitatesin the finished non-oriented silicon steels with different sulfur contents were studied using SEM/TEM-EDS and image analysis software, and the magnetic properties of the finished steel were measured. The statistical results indicated that the main inclusions in the experimental steels are AlN, (Al, Si)_xN_y, MnS, and AlN/(Al, Si)_xN_y-MnS composite inclusions. There are small amounts of composite oxides containing MgO·Al₂O₃ or oxides-MnS composite inclusions. The precipitates are mainly composed of Cu_xS and MnS+Cu_xS composite precipitates. The segregation of [S] at the solidification front decreases with the decrease in sulfur content, resulting in a decrease in the number of nitrogen sulfides in the steel. The research results indicate that the lower the sulfur content is in the steel, the higher the residual nitrogen content is in the steel, and the number density of nitrides increases. The change of sulfur content has little effect on the number of oxides, sulfides, and oxysulphides in the fully deoxygenated steels. During the solidification process of the molten steel, the precipitation amount of MnS decreases in sequence with the decrease of sulfur content, so the precipitation amounts and size of inclusions containing MnS are changed, resulting in a decrease in the total amount of inclusions and an inhomogeneous distribution of inclusion size. The difference of MnS-bearing inclusions precipitating mainly originates from the segregation difference of [S] until the solidification ratio of the liquid steel is higher than 0.7, and when the content of sulfur in the steel decreases to 15×10^-4% or less, the segregation difference of [S] at the solidification front is very small. When sulfur content is 10×10^-4%, the number density of the inclusions and precipitates in the experimental steels is less than those in the other samples. The average size of the inclusions is about 2.0 μm and the average size of the fine precipitates is 52 nm. The excellent number and size control effect of inclusions and precipitates are in return with the best magnetic properties of the 10×10^-4% S-bearing samples, and the iron loss P_1.5/50 is 4.16 W/kg and the magnetic induction B₅₀ is 1.751 T. The iron loss P_1.5/50 increases by 0.27 W/kg and the magnetic induction B₅₀ decreases by 0.040 T after sulfur content in the steel decreased to 5×10^-4%, which is related to the increase of aluminum and nitrogen contents and inclusions above 3 μm caused by deep desulfurization of liquid steel. Excessive reduction of sulfur content of the non-oriented silicon steels in smelting process deteriorates the magnetic properties of the steels.