The construction of kinetic equations for the phase transition of C-Mn steels is of great significance in guiding its microstructure regulation and mechanical property enhancement. Continuous cooling transformation behavior of C-Mn steel was investigated by Gleeble-3500 thermal simulator, optical microscope (OM), field emission scanning electron microscope (SEM). The conventional JMAK equation was optimized based on the phase transformation products. The results show that the C-Mn steel was cooled at a rate of 0.5-50 ℃/s after complete austenitising at 1 000 ℃. With the increasing cooling rate, the supercooled austenite undergoes the phase transformation of ferrite, pearlite, bainite and martensite successively. The organisation is fully martensitic when the cooling rate is greater than 20 ℃/s and the corresponding transformation temperature intervals are 728-516, 517-400 and 330-190 ℃. When the cooling rate increases, the critical time span t₀ of the phase transition product transformation decreases exponentially, with an exponential fit as t₀=120.6 v^-0.83. Based on the influence of different phase transition products on the n value,the functional equation of the n value on the cooling rate was established under different cooling rates. The kinetic equations for the JMAK phase transition were constructed. Eventually, model prediction accuracy has been improved. The JMAK equation has a driving role in describing the multiphase transformation process under non-isothermal rapid cooling conditions.

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.

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.

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 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.

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.

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).

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.

With the development of the aerospace technology, the reverts of Ni-based superalloy is accumulated increasingly. To efficiently mitigate the waste of precious metals and promote the circular economy, it is crucial to control the composition and properties of revert alloys to be equivalent to those of virgin alloys through purification and utilization technology. However, with the wide variety and complex composition along with the impurities and flaws presented in the reverts, the difficulty is rising in purifying and utilizing the Ni-based superalloys. The effects of revert proportion and recycle times on the composition, microstructure and mechanical properties are summarized. The worldwide pretreatment technology and melting purification methods for revert are discussed , focusing on the cleanliness analysis method. Furthermore, some valuable suggestions are provided on enhancing the recycling of superalloy revert.

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.

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.

Electrolytic ironmaking from aqueous solution, an emerging hydrometallurgical technology, aims to produce pure iron by electrolytic reduction of iron compounds, offering significant environmental and energy advantages. In recent years, with the continuous advancements in materials science, electrochemical technology, and energy systems, substantial research progress has been made in electrolytic ironmaking processes and techniques. However, certain technical challenges remain. For instance, the gas element content in the electrolytic products is high, necessitating further treatment to achieve higher purity iron. The stability of the electrolyte is poor, and ferrous ions are prone to oxidation and degradation.The state-of-the-art principles, processes, equipment, and control technologies of electrolytic ironmaking both domestically and internationally were reviewed. Corresponding solutions to the technical challenges have been suggested. For example, increasing the electrolysis temperature could reduce the gas element content in the products, thereby shortening the process, and adding stabilizers (such as ascorbic acid and sodium citrate) could inhibit the oxidation of ferrous ions. Finally, recommendations and outlooks for the future advancement of electrolytic iron production are given,including improvements in electrolysis equipment and the shortening of process flows to save energy consumption and intelligent systems implemented for real-time monitoring and other applications.

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.

The iron and steel industry is a crucial foundational sector in China's national economy and a major carbon emitter, producing 1.3 billion tons of CO₂ annually, which accounts for 15% of the nation's total carbon emissions. Annual steel slag generation also reaches 150 million tons. Utilizing the bulk steel slag generated by the industry itself to sequester significant amounts of CO₂ enables“treating waste with waste”, provides an outlet for captured CO₂, and makes deep decarbonization of the steel industry feasible. The major advantages and existing problems of steel slag carbonation technologies are reviewed, which could be categorized them into two main types (direct and indirect carbonation). These can be implemented through three specific approaches: hot slag direct carbonation, cold slag direct carbonation, and cold slag indirect carbonation. It could be pointed out that both hot steel slag direct carbonation technology and cold steel slag indirect carbonation technology are suitable for China's context in achieving its dual-carbon goals. Hot slag direct carbonation seamlessly integrates with existing steel slag treatment processes in steel plants. Cold slag direct carbonation has relatively lower carbonation efficiency and capacity due to its lower reaction temperature, whereas cold slag indirect carbonation achieves higher-value utilization of the slag.

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 ℃.

Grain oriented electrical steel (GOES) is one of the most fundamental and important materials in the construction of modern power energy systems, playing an indispensable role in high-efficiency power transmission and transformation. Due to its complex manufacturing process, high precision requirements for equipment functionality, and stringent process control challenges, producing high-performance GOES necessitates significant breakthroughs both in manufacturing equipment and process technologies. The technological advancements and development of GOES throughout its entire production process were explored, including composition design, microstructure control, and processing techniques. The roles of alloying elements in GOES and the key manufacturing technologies to achieve the target composition were specifically analyzed, the microstructural evolution during the rolling and heat treatment processes was summarized, the impact of critical process parameters in rolling and heat treatment on the microstructure of GOES was investigated, and the characteristics of key post-processing coatings and magnetic domain refinement technologies were outlined. Finally, in light of the severe challenges faced by GOES development, the future research directions and development trends in this field were proposed.

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.

Super-high bed sintering is an important route to reduce carbon emissions in the steel industry. However, as the sintering bed depth increases in practice, the severe inhomogeneity of sinter products adversely affects the blast furnace production. Joint analysis of mixture and sinter was carried out on more than 10 industrial sintering machines in China with bed depth of not less than 900 mm. It is revealed that the inhomogeneous quality of sinter products mainly manifested in the longitudinal direction, transverse direction, and between the strands. The root reason is that the uneven liquid phase composition and heat caused by unreasonable distribution of mixture particle size, chemical composition, and air cannot satisfy the requirements of liquid phase homogeneous mineralization. To address the above problems, an ideal bed structure matching the liquid phase and heat was developed. Besides, the optimized ore blending technology for liquid phase composition regulation, the enhanced mixing and granulation technology, synergistic feeding technology, and air reorganization sintering technology were developed to achieve this bed structure. By optimizing the chemical composition of liquid phase, regulating the distribution of liquid phase within the sintering bed, and matching the heat with the liquid phase quantity, the efficiency of heat and suction was improved, and homogeneous mineralization was achieved. After the implementation of those technologies, the solid fuel consumption was reduced by 1.2-7.9 kg/t, the tumble index increased by 3%-6%, and the difference of tumble index within the sintering bed was reduced to 5.08%. Furthermore, the metallurgical performance of the sinter improved, with the reduction disintegration index RDI_{+3.15 mm} increasing by 10% and the difference of RDI_{-0.5 mm} decreasing to 1.99%. The productivity of the blast furnace improved, and the solid fuel consumption was reduced by 6.58 kg/t at the highest.

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 stiffness of rolling mill has an important influence on the control of plate thickness and shape and the stable operation of rolling. In order to study the stiffness of the rolling mill system and the change of rolling force during the actual rolling process of the 1850 Furnace Coil Rolling Mill, based on the finite element analysis, a thermal coupling model of the rolling process of the furnace coil rolling mill was established under the extreme rolling conditions while taking into account the influence of rolling temperature. Then, the stiffness, stress and strain of key parts during the operation of the rolling mill under the influence of multiple factors were calculated. Three sets of numerical simulation were carried out according to the maximum rolling force in the rolling schedule. The deformation of each part of the rolling mill fluctuates up and down with the change of rolling force. The real-time stiffness of the rolling mill system is calculated based on the rolling force and the total vertical deformation in the rolling process. Using the average rolling force and the average deformation, the stiffness of the rolling mill is 6 078, 6 089 and 6 077 kN/mm, respectively. The results show that even though the average rolling force and total deformation in the three rolling procedures are different, the stiffness values are basically the same.

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 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.

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.

To further understand calcium treatment technology, industrial experiments were carried out in the refining process of Q355 Ti-bearing Al-killed steel grades, and the inclusions in steel and the cleanliness of the steel were investigated considering different feeding lengths of Ca wires. The results show that the solid inclusions during the refining process transformed into the liquid CaO-Al₂O₃ inclusions, and the feeding length of calcium wires did not affect the evolution trend of the inclusions. After calcium treatment, the total oxygen content of the steel increased, while the average size of the inclusions decreased. Furthermore, both the occurrence of the large-sized CaO-Al₂O₃ inclusions and the degradation of refractory wereaggravated by calcium treatment. After ensuring steel castability, a smaller feeding length of Ca wire is beneficial for the cleanliness of the steel. If there are no castability problems, calcium treatment can even be eliminated.

In order to investigate the effect of austenitizing process on the grain growth behaviors of Nb-Ti microalloyed steel, thermal simulation experiments were conducted to study the austenite grain growth behavior of the experimental steel within the range of austenitizing temperature (1 140-1 220 ℃) and holding time (180-540 s). The mathematical models for austenite grain growth and its distribution were established. The results indicate that when the holding time is kept constant, the austenite grains tend to grow larger and become more uniformly distributed. When the austenitizing temperature is held constant, prolonging the holding time slows down the growth rate of austenite grains, and the size distribution of the austenite grains will also tend to become more uniform. The mathematical models for the average austenite grain size and its distribution closely match the measured values. Contour plots are generated for the average austenite grain size and grain size distribution parameter under different austenitizing process conditions, which provide a theoretical foundation for determining reasonable austenitizing processes for experimental steels.

The microscopic mechanism of non-equilibrium segregation has not been fully elucidated. The solute-vacancy binding energy is an important parameter which is closely related to physical phenomena such as grain boundary segregation and diffusion. However, the experimental data are difficult to obtain. A database of solute-vacancy binding energy in fcc Fe based on an Anti-ferromagnetic double-layer (AFMD) structure was established based on first-principles density-functional theory. The correlation analysis of this binding energy shows a strong positive correlation between the first nearest-neighbor (1NN) solute-vacancy binding energy and solute impurity volume for transition metal solutes, and a strong positive correlation between the 1NN solute-vacancy binding energy and electronegativity for main-group elements. The calculated results successfully explain the reason of non-equilibrium grain boundary segregation of B, P and S. Results also predict that Si and As are also likely to form solute-vacancy complexes. The results not only reveal the microscopic mechanism of non-equilibrium grain boundary segregation, but also provide guidance in grain boundary engineering for utilizing alloyed elements.

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.

In order to meet the requirement of real-time acquisition of 3D flow field data in ladle bottom-blowing refining, a fast prediction model of 3D flow field based oncomputational fluid dynamics (CFD) and proper orthogonal decomposition (POD) was established. The three-dimensional flow field data of single-nozzle bottom blowing of ladle were simulated and calculated by establishing the numerical model and the water model, and the data set was established. The mode and mode coefficient of the data set were extracted by the POD method. Through the back propagation neural network (BPNN), the mapping relationship between operating parameters and modal coefficients was constructed, and the velocity field and three-phase volume fraction in the bottom-blowing ladle can be predicted quickly. The results show that the proposed model can reconstruct the main characteristics of the flow field in the ladle through a few modes. The POD-BPNN prediction model has a high accuracy of calculation results, and the average relative error of calculation results is less than 4%. The calculation speed of the model is fast, and the average calculation time to obtain the flow field in the ladle is reduced from about 246 h required by CFD simulation to about 54.6 h by the POD method.

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.

In order to investigate the effect of Al content on oxygen content and inclusions in 2507 duplex stainless steel, ingots with different Al contents were melted using a laboratory vacuum induction furnace. The O content in the steel was detected, and the morphology, composition, and size of inclusions were observed using a scanning electron microscope and an energy spectrometer.The results were statistically analyzed, and the effect of Al content on the type and content of inclusions was calculated using FactSage software. In the study of the effect of Al content on O content, it was found that the O content in steel first decreased rapidly with the increase of Al content, and the O content was kept at about 0.001 mass% when the Al content was 0.1 mass% to 0.3 mass%, and gradually increased with the increase of Al content. In the study of the effect of Al content on inclusions, it was found that at w(Al_t)≤14×10^-6, Al in the steel is not enough to generate Al₂O₃ inclusions, and Si, Mn and Cr elements will react with O to generate SiO₂-MnO-Cr₂O₃ inclusions; when the Al_t content is 44×10^-6, in addition to the SiO₂-MnO-Cr₂O₃ class inclusions,aggregated Al₂O₃ inclusions began to appear in the steel, and at the same time, SiO₂-MnO-Cr₂O₃ inclusions that were not completely reduced by Al due to the lack of Al were observed; when the Al_t content was higher than 98 ×10^-6, the Al in the liquid steel was sufficient to reduce all of the SiO₂-MnO-Cr₂O₃ inclusions, and all the inclusions observed in the steel were Al₂O₃ inclusions. In addition, the sizes of inclusions in steel at different Al contents were counted, and it was found that the average size of SiO₂-MnO-Cr₂O₃ inclusions was larger than the average size of Al₂O₃ inclusions when the Al content in steel was low, while the maximum and average sizes of Al₂O₃ inclusions gradually increased with the increasing Al content in steel. According to the results of thermodynamic calculations, in order to obtain 2507 duplex stainless steel with lower O content and smaller inclusions size, it is necessary to control the aluminum content of steel above 72×10^-6.

When low-pressure carburizing technology is applied to the third-generation ultra-high-strength gear steel, there still exist process problems such as carbide aggregation, austenitic soft layer, contradiction between carburized layer quality and thickness. This study investigates the effect of the introduction of the "double carburizing" process on the quality of the carburized layer, hardness and microstructure of 1900 MPa aerospace low-pressure carburized gear steel. SEM, XRD, EPMA, EBSD and TEM techniques were employed to precisely characterize the microstructure from carburized layer to core. The results show that after the introduction of the "double carburizing" process, no network distributed carbides existed, the overall carbon content of carburized layer increased, and the hardness of carburized layer increased by ~20 HV. The micron-sized block or strip shaped Cr-rich carbides at the same depth position increased, and this type of carbides located in the surface layer was mainly transformed from M₂₃C₆ to M₇C₃. The submicron-sized spherical M₆C carbides slightly decreased in quantity, meanwhile substantial amounts of submicron-sized M₂₃C₆ carbides, nanometer-scale MC and M₆C carbides are generated. At the same time, the carburized shell layer thickens and the transitional layer narrows. In addition, the hardness of the core of the "double carburizing" specimen is slightly reduced due to the decrease in dislocation density.

In response to the phenomenon of “desulfurization and resulfurization” of steel during the process of adding scrap steel in a diversified smelting mode of a certain enterprise in China, the composition of refining slag was optimized reasonably. Firstly, the thermodynamic software FactSage 8.1 was used to simulate the iso-oxygen lines of CaO-SiO₂-Al₂O₃-5%MgO slag system and Q235 steel equilibrium was simulated and calculated under the temperature condition of 1 600 ℃. Meanwhile, the sulfur capacity and sulfur distribution ratio of the slag system were calculated by using the optical basicity of the refining slag to measure the desulfurization ability of the refining slag. Secondly, high-temperature equilibrium tests on steel slag were carried out using five different designed refining slags in the laboratory. After the experiment, the composition of the refined slag was determined through XRF analysis, and the elements within the steel samples were analyzed using ICP-AES, an oxygen-nitrogen analyzer, and a carbon-sulfur analyzer. Field emission scanning electron microscopy was employed to study the structure and makeup of inclusions within the steel samples. A statistical evaluation was conducted to assess the number and dimensions of these inclusions. Finally, industrial experiments were conducted to verify the results. The results show that by optimizing the composition of the slag system, the mass fractions of CaO, SiO₂, Al₂O₃, and MgO are controlled within the range of 47.7%-55.2%, 0-20.5%, 26.85%-55%, and 4%-7%, respectively. The mass fraction of dissolved oxygen in the steel can be controlled within 0.001%. A slag system composed of 54.27%CaO, 7.43%SiO₂, 33.3%Al₂O₃, and 5%MgO was selected, achieving a desulfurization rate of 54.73% and reducing the total oxygen in steel to 0.002 1%. The experimental results validated the accuracy of the thermodynamic calculations.

Pulverized coal injection technology is the main technology to reduce iron-making production costs and improve blast furnace (BF) smelting efficiency. Biomass used for BF injection is one of the key technologies to achieve low-carbon iron-making due to renewable low-carbon energy source property. Three types of biomass hydrochar produced industrially were used to investigate the feasibility of applying the hydrothermal carbonization products (hydrochar) of low-quality biomass to BF injection. The results showed that hydrochar has high volatile content and low calorific value, while orange peel and olive pomace hydrochar have low ash and alkali metal content, which can be used as substitutes for bituminous coal for BF injection. The experiments of hydrochar mixed with anthracite show that hydrochar has strong explosiveness. Mixing anthracite with hydrochar can effectively suppress explosiveness. When the proportion of hydrochar added is less than 20%, the mixed sample has no explosiveness. Hydrochar has a lower ignition point and excellent combustion performance. As the mixing ratio of hydrochar increases, the ignition point of the mixed sample decreases, and the combustion curve moves towards the low-temperature zone, gradually improving the combustion performance. Based on the above research, hydrochar produced from orange peel and olive pomace can be used as BF injection fuel, and the proportion of hydrochar added to mixed anthracite should be controlled below 20%.

In order to meet the high temperature performance requirements of high power density diesel engine block and cylinder head materials, changes of mechanical properties and microstructure of high strength vermicular graphite cast iron for diesel engine cylinder head after different thermal exposure temperatures of 350, 500 ℃ and different holding time of 0-1 000 h were studied. The results show that after thermal exposure, the tensile strength R_m of the compacted graphite cast iron test piece decreases with the increase of holding time, and the elongation A increases with the increase of holding time. The tensile strength R_{m(25 ℃)} and elongation A_{25 ℃} of the specimens at room temperature decreased by 20.0% and increased by 41.7%, respectively after thermal exposure at 350 ℃ for 1 000 h. The high temperature tensile strength R_{m(200 ℃)} and elongation A_{200 ℃} decreased by 20.2% and increased by 125% respectively compared with those without heat preservation. The room temperature tensile strength R_{m(25 ℃)} and elongation A_{25 ℃} of the specimens exposed at 500 ℃ for 1 000 h decreased by 46.7% and increased by 36.1%, respectively, compared with those without heat preservation. The high temperature tensile strength R_{m(200 ℃)} and elongation A_{(200 ℃)} decreased by 14.6% and increased by 50%, respectively, compared with those without heat preservation. With the increase of thermal exposure time, the amount of pearlite in the matrix of compacted graphite cast iron gradually decreases, and the amount of ferrite gradually increases, which is the main reason for the change of microstructure and mechanical properties.

Q890 high-strength structural steel was used to explore the influence of intercritical quenching temperature and tempering temperature on the microstructure and precipitates by using ThermoCalc software, transmission electron microscope and tensile testing machine. The results indicate that with decreasing the intercritical quenching temperature (840, 800, 760 ℃), the proportion of ferrite increases, and the types of the precipitated particles increase, and the average diameter and the volume fraction of the precipitated particles decreases. After 840 and 800 ℃ quenching, the strength of the tested steel is similar. After reducing the quenching temperature to 760 ℃, the yield strength of the tested steel decreases by about 200 MPa, and the fracture elongation increases to 18.5%. With the increase in tempering temperature (200, 400, 600 ℃), the dislocation density of the texted steel decreases, and the matrix softens; the type of the precipitated particles increases, and the average diameter and the volume fraction of the precipitated particles increase, and thus the precipitation strengthening is significantly increased. As the tempering temperature increases, the yield strength of the tested steel gradually decreases (1 210, 1 120, 817 MPa), and the fracture elongation gradually increases (14.0%, 14.2%, 21.8%).

Controlling the size of slag eye by bottom blowing in steel ladle can improve the quality of steel liquid. Based on the argon bottom blowing process in steel ladle, a three-dimensional unsteady multiphase flow water model is established by coupling the Discrete Phase Model (DPM) and the Multiphase Flow (VOF) model. The slag eye size and slag eye interface velocity obtained from numerical simulation are validated and analyzed using a 1:5 water model. The research investigated the impact of different parameters (bottom blowing flow rate, oil layer thickness, and bottom blowing position) on the distribution of slag eye size and slag eye interface velocity. Finally, the relationship between dimensionless slag eye area and dimensionless flow rate was obtained through data fitting methods. The results indicate that the slag eye area gradually increases with the increase of blowing flow rate and the decrease of oil layer thickness, with a more significant effect for higher bottom blowing flow rates. A greater eccentricity of the nozzle leads to a more noticeable change in slag eye area with respect to blowing flow rate. For eccentric bottom blowing, there is a critical flow rate value, beyond which the slag eye area decreases. For instance, with an oil layer thickness of 25 mm and a blowing flow rate of 2.26 L/min, the slag eye area decreased by 180 cm² compared to that when the blowing flow rate was 1.87 L/min.

The coupling effect between temperature and stress can cause excessive deformation of refractory materials, thereby endangering the stability of the furnace lining structure. Therefore, accurate measurement of deformation is essential for designing and predicting furnace lifespan. The load softening temperature and creep rate are the main methods for evaluating the high-temperature compression deformation of refractories at low stress levels. However, applying these methods directly to high stress levels may lead to issues such as bent pins, broken pins, and gasket deformation. To address this challenge, a baseline calibration method based on the displacement recording function of the pressure machine for evaluating high-temperature compression deformation of refractories was proposed, and the principle and rationality of this method were elaborated in detail. According to the softening temperature of fireclay bricks, the high-temperature compressive strength was measured at different temperatures, and the measurement deviation was compared. The minimum deviation was 3.2%. By using CT technology to detect the internal pore distribution of the sample after the experiment, the closed-cell porosity increased from 3.43% to 8.10%. Combined with phase and typical morphology analysis, it further indicates that the baseline calibration method has high accuracy and practicality. Based on the experimental results, the judgment criteria and definition of high-temperature compressive strength were proposed, providing theoretical support for the research of refractory materials and the design of high-temperature furnace linings.