The European Union （EU）'s Carbon Border Adjustment Mechanism （CBAM） has been officially released, which has attracted extensive and sustained attention from all sectors of society. Among the six categories of products covered by CBAM, iron and steel products are the most affected due to high carbon emissions and large export volume. Therefore, it is extremely urgent to quantitatively analyze the possible impact of CBAM on China's iron and steel exports and explore countermeasures. From 2020 to 2023, China's iron and steel products exports worldwide show a trend of volume increase and price decrease, and the export destinations are mainly distributed in the Association of Southeast Asian Nations （ASEAN）, South America and the EU. In 2023, China's total iron and steel products directly exported to the EU grew less than expected, indicating that CBAM has had a negative impact on China's iron and steel exports to the EU. China's iron and steel products are indirectly exported to the EU through Southeast Asia, so the comprehensive impact of CBAM o n China's iron and steel exports must be considered in parallel with indirect exports. The main target countries of China's iron and steel exports to the EU are Italy, Belgium and Germany. In 2023, China's total exports volume to the three countries fell sharply year-on-year, which is far more than the overall situation of iron and steel exports to the EU, indicating that the main importers of iron and steel products purchased from China in the EU are gradually changing. In addition, due to the high unit price of iron and steel products exported to Germany and France, the overall export volume is stable, indicating that high value-added iron and steel products have strong competitiveness in the EU. Finally, the impact of CBAM implementation on China's iron and steel exports is analyzed, and the response work is proposed from the four directions of adapting to the carbon market, keeping up with international carbon-related policies, continuous process optimization and carbon reduction, and building a full-process green supply chain, aiming to help China's iron and steel industry comprehensively respond to international carbon-related trade barriers, and provide reference and support for the high-quality and sustainable development of the industry.

The iron and steel industry occupies a crucial position in the process of economic and social development. With the continuous growth of China's iron and steel production, the subsequent treatment problem of steel slag has become increasingly prominent. Due to the problems of poor stability, high abrasion resistance and low cementation of steel slag, the treatment and resource utilization of steel slag are restricted, and a large amount of steel slag is piled up for treatment, which not only occupies land resources, but also harms the surrounding environment and residents' lives. In the context of "green sustainable development" and "carbon neutral", in order to meet the urgent needs of modern steel mills for environmental protection and resource reuse, the development of steel slag treatment and resource utilization technology is imperative. It reviews the research progress of steel slag treatment technologies and resource utilization, and introduces the current mainstream treatment technology of steel slag, including pretreatment process, steel slag modification process and wet treatment process. The technical characteristics of different treatment processes, resource recovery and potential application pathways of products are elaborated in detail, and the technical advantages of different treatment processes are analyzed. In addition, the exploration and research progress of steel slag in the field of environmental remediation are discussed and analyzed, pointing out the application potential of steel slag in this field and the future research direction. The resource utilization of steel slag in China is still facing many problems such as pre-treatment and technological breakthroughs for the expansion of high-quality application areas. The purpose is to analyze the overview of steel slag treatment technology and resource utilization, and to propose that the future research on steel slag, while focusing on the full use of sensible heat and the recovery of valuable resources such as iron, should focus on and strengthen the basic research on the regulation of the evolution of steel slag composition and physical phase. On this basis, new technologies should be developed in the direction of environmental remediation, preparation of new materials and high-value products to expand the high-quality utilization of steel slag and improve the comprehensive utilization rate of steel slag.

High casting speed is the hot research topic in the field of slab continuous casting with the direct effect on equipment design, manufacturing processes, product quality, cost control and energy saving and consumption reducing. In comparison to the level of high casting speed in abroad, the technical index in domestic plants is still behind. However, some researchers succeeded in exploring high speed slab continuous casting and improved the casting speed to higher than 1.5 m/min, even over 2.0 m/min ranking as the advanced level. High speed slab continuous casting is actually a systematical engineering, with great demand on the supporting technologies to make it run at high efficiency, high safety and high stability. The tailored design and optimization should be carried out including submerged nozzle structure parameters, mold oscillation, mold flux, mold cooling, flow control by electromagnetic field and level fluctuation compensation. The results in previous studies show that the key factors influencing the product quality and safety and stability in high speed continuous casting are the steady flow and heat transfer of liquid steel in the mold, together with the even growth and good lubrication of the shell. Low carbon steel and hyper-peritectic steel are preferentially employed in the trial of high speed continuous casting, and the casting speed of hypo-peritectic steel and high carbon steel is still falling behind, although it increases obviously. The definition of high speed continuous casting is different with the variation of steel grade, strand type, equipments, operation, and technology, and the level of high casting speed is also different in different era. High speed mold metallurgy technologies are the core guarantee for high efficiency slab continuous casting. It is expected that the contents and conclusions of the study can be the theoretical and technological references for the experts and researchers regarding the issue of high speed continuous casting.

In order to meet the diversified needs of high-strength dual-phase steel users in automobile manufacturers, two kinds of high-strength dual-phase steels with different microstructure characteristics of F/M and B/Ar were obtained, adopting reasonable chemical composition design and process control. The process design principles and microstructure characteristics of F/M and B/Ar high-strength dual-phase steels were studied by means of SEM, TEM, tensile and hole expansion tests, and the influencing factors of mechanical properties were analyzed. The results show that the annealing temperature of F/M dual-phase steel is 810 ℃ in the range of （A_C1+A_C3）/2±8 ℃（A_C1 and A_C3 are the start and end temperatures of austenite transformation during heating, respectively）, which is mainly composed of 47% ferrite, 46% martensite and 7% block retained austenite. The ferrite has two forms of recrystallized ferrite and proeutectoid ferrite, and the grain size is 2.5-4.0 μm and 1.0-2.5 μm, respectively. The annealing temperature of B/Ar dual-phase steel is set to 900 ℃ in the single-phase austenite region. The microstructure is mainly composed of 84% bainite and 16% second-phase retained austenite. The bainite is based on the original γ grain. The phase transformation is formed, and the retained austenite is characterized by lamellar or discontinuous block. There are obvious differences in microstructure morphology between F/M and B/Ar dual-phase steels. The coordinated deformation effects of each phase structure are different during the deformation process, which affects its mechanical properties. The tensile strength can be controlled at the level of 1 000 MPa by both processes. The nano-sized VC precipitated phase particles with a diameter of 4-13 nm are dispersed in the matrix, and the precipitation strengthening amount exceeds 220 MPa, which interacts with high-density dislocations, and finally improves the strength and plasticity of the material. The tensile strength of F/M dual-phase steel is 1 035 MPa, and the elongation after fracture is 18.7%. Compared with F/M dual-phase steel, the tensile strength of B/Ar dual-phase steel increases by 111 MPa to 1 146 MPa, and the product of strength and plasticity reaches 19.83 GPa·%. It has the characteristics of high yield ratio and hole expansion rate, which are 0.709 and 38%, respectively.

Under the "carbon peaking and carbon neutrality" target, scrap steel is becoming more and more important in the global steel industry due to its green and low-carbon characteristics. Enhancing the recycling level of scrap steel has become a key strategy for the transformation and upgrading of the steel industry. Currently, most research is focused on the contribution of using scrap steel to reduce emissions in the steel industry. However, there is still a lack of research on the development trends of the scrap steel industry and the carbon emissions in its production process. Based on the "emission-factor approach", the carbon emission level of scrap recycling process was quantitatively analyzed. Considering the three factors of energy efficiency, cost-effectiveness and environmental impact （especially carbon emissions）, the optimization model of scrap steel recycling process aiming at maximizing enterprise profit was established. The impact of scrap steel market prices, carbon trading prices, equipment energy consumption, and renewable energy applications on enterprise profits and carbon emissions was analyzed. The results of the study show that when carbon emissions are taken into account in production planning, the carbon emissions of scrap steel enterprises are reduced by 12.23%. At the same time, with the rapid construction of the national carbon market system, scrap steel enterprises can increase profits by selling excess carbon allowance indicators. While steel enterprises need to purchase extra carbon indicators, in which enterprises using short-process steelmaking reduce carbon trading costs by 55.6% compared with long-process enterprises. The increase in the proportion of photovoltaic power generation can achieve better carbon emission reduction effect. When the proportion of photovoltaic power generation is increased to 71.3%, carbon emissions can be reduced by 51.51% and the cost of purchased electricity can be reduced by 63.2% compared with the current scheme. Since the cost of purchasing raw scarp steel accounts for more than 70% of the total cost, market price fluctuations have a much greater impact on company profits than the fluctuations in energy costs or carbon emission income. When the purchase price and the selling price of scrap steel increase proportionally, the enterprise profit increases with the growth of scrap steel price. This study aims to provide guidance for scrap steel enterprises to optimize production planning in the context of "carbon peaking and carbon neutrality, "thereby achieving a win-win situation in both economic and environmental benefits.

In order to address the common problems of uneven temperature distribution of rolling rolls, frequent fluctuations in hot roll profiles, and local hotspots in traditional cooling modes of hot rolling, a finite difference model for segmented cooling of work rolls in hot rolling was established based on the dynamic thermal conductivity characteristics of online rolling rolls to quantitatively adjust the transient temperature gradient of rolling rolls and online hot roll profiles, and better control the horizontal thickness difference accuracy of products. Firstly, a contact thermometer was used to quickly measure the temperature along the horizontal direction of the work roll, and the convective heat transfer coefficient of the online temperature field was reverse calculated. Combined with actual operating parameters, the temperature field of the rolling process was simulated. By comparing the simulation results with the on-site measured data, the reliability of the model was verified. Subsequently, taking into account key factors such as opening water volume, bandwidth, and rolling time, a comprehensive analysis was conducted on the dynamic changes in roll temperature and thermal convexity during the hot rolling process. The results show that increasing the total cooling water opening ratio by 20% results in a 6.5 ℃ decrease in roll temperature, a 32.0 μm decrease in thermal convexity; a 10 s decrease in rolling time, a 5.1 ℃ decrease in roll temperature, and a 24.3 μm decrease in thermal convexity. However, the uniformity of thermal expansion of wide strip steel is better. By comparing three typical horizontal segmented cooling modes, it is found that when the horizontal distribution of cooling water is adjusted online, the roll temperature and thermal convexity dynamically change accordingly. Choosing the appropriate segmented cooling mode according to the working conditions can accurately adjust the overall roll temperature and horizontal temperature difference to the set range. An important basis is provided by this study for the optimization for the selection of segmented cooling modes and comprehensive optimization of plate shape and convexity for multi stand hot rolling. A theoretical foundation is laid for the design of high-efficiency hot rolling cooling devices and multi condition coupled segmented cooling systems.

Electroslag remelting is a method to purify molten steel, using the resistance heat generated by the current passing through the slag as a heat source for smelting. The products prepared by electroslag remelting have the advantages of high purity, dense structure, uniform composition, and smooth surface, so electroslag remelting is widely used in the preparation of high-end metal materials. To ensure the conductivity of the slag, the electric slag system contains a certain amount of CaF₂, which causes severe volatilization during the smelting process and pollutes the environment. The volatilization of fluoride causes significant fluctuations in slag composition, which affects the smelting process and product quality. From the aspects of slag composition, smelting environment, thermodynamics and kinetics, the factors affecting the volatilization of fluoride and the effective methods to reduce the volatilization of fluoride in the slag system are discussed. The effects of CaF₂, w（（CaO））/w（（SiO₂）） and w（（CaO））/w（（Al₂O₃）） on the volatilization of slag system are introduced. Reducing the content of CaF₂, increasing the w（（CaO））/w（（SiO₂）） and decreasing the w（（CaO））/w（（Al₂O₃）） in the slag would effectively reduce the volatilization of fluoride in the slag. And the possibility of using alkali metal oxides （Li₂O, Na₂O, K₂O）, TiO₂ and B₂O₃ instead of CaF₂ to develop low fluorine slag is discussed. One of the important directions for future development of low fluorine/non fluorine slag is to replace CaF₂ with Na₂O, TiO₂, B₂O₃, etc. The effects of smelting temperature and environmental humidity on the volatilization of fluorine-containing slag are reviewed. Reducing the smelting temperature, increasing the heating rate, premelting the slag system and maintaining dryness could effectively inhibit the volatilization of fluoride. On the basis of investigating the current research status of volatilization thermodynamics and kinetics of electric slag system, the applicability of the slag molecular ion coexistence theory to calculate the activity of slag system components is introduced, the kinetic mechanism of slag system volatilization is summarized, and the kinetic limiting links of fluorine containing slag volatilization in electric slag remelting process are summarized. The molecular ion model has high accuracy in calculating the activity of common slag system components, and its applicability to other special slag systems still needs further verification. Future research on volatilization kinetics of slag systems should focus on the mass transfer process of anions and cations participating in volatilization reactions from the main body to the reaction interface, as well as the nucleation, growth, and bubbling processes of reaction products, in order to reduce fluoride volatilization.

The zero reforming of coke oven gas and direct reduced process is of great significance for the green transformation of steel enterprises, with significant energy-saving and emission reduction effects. Due to the high composition of φ（H₂）/φ（CO） and a certain amount of CH₄ in the reduction gas of this process, the reduction atmosphere conditions of this process were simulated, and the effects of different conditions on the metallurgical properties indicators such as reducibility, compressive strength, reduction swelling index, and whole ball index during the reduction process of pellets were explored. This is of great significance for the smooth operation and energy conservation of this process. The results indicate that, as the reaction temperature increases, the reduction degree, carbon content, and swelling index increase, while the compressive strength and whole ball index decrease. After the reduction temperature increased from 850 ℃ to 950 ℃, the increase in carbon content leads to severe expansion and fragmentation of the pellets in the later stage of the reduction reaction, and the reduction degree corresponding to the maximum swelling index changes from 40%-50% to about 60%. After replacing CO with an equal amount of H₂, in the early stage of the reaction, due to the increase in reduction rate, the swelling index gradually increases, while the compressive strength and whole ball index decrease. In the later stage of the reaction, due to the inhibitory effect of H₂ on the growth of iron whiskers and carbon deposition, the swelling index of the pellets decreases, while the compressive strength and the whole ball index increases. By using equal amounts of N₂ to replace CH₄, the reduction degree, carbon content, and swelling index of the pellets decrease, while the compressive strength and whole ball index increase. After the reduction degree of the pellets exceeds 40%, the range of changes in various metallurgical properties with the change of φ（CH₄） gradually increases. When the reduction time of pellets under various conditions is 20-40 min and the reduction degree is 60%-80%, the corresponding changes in metallurgical properties reach their extreme values. During the production process, attention should be paid to the indicators of pellets in this area. The carbon evolution process of CH₄ has a certain deteriorating effect on the metallurgical properties of pellets, and φ（CH₄） in the vertical furnace should be controlled.

Differential scanning calorimetry （DSC） is a precise technique for quantitatively analyzing thermophysical changes and thermal transition information in materials during thermal variations, characterized by high accuracy, rapid testing, and minimal sample requirements. The advancements in DSC have significantly broadened the scope of material property testing in steel and alloy research, facilitating a deeper investigation into the thermodynamics and kinetics of material thermal transitions. It commences with the fundamental theory of DSC, detailing its classifications and signal compositions, and offers a comprehensive overview of DSC's current applications in steel and alloy research. The advantages and limitations of DSC, particularly in the study of specific heat, phase transitions, precipitation and decomposition of secondary phases, and the glass transition in amorphous alloys are discussed. The integration of DSC with other techniques is also explored. Furthermore, it summarizes the current state of kinetic research utilizing thermal analysis data from DSC, including studies on activation energy and transition mechanisms in alloy phase transitions, as well as the development of kinetic models for alloy transformations. A comprehensive analysis of the thermophysical parameters of steels and alloys through DSC, combined with an in-depth understanding of the thermodynamics and kinetics of alloy phase transitions, is expected to provide robust theoretical support for the development, manufacturing, and application of alloy materials.

In order to study the characteristics and formation mechanism of inclusions in the smelting process of Fe-Cr-Ni corrosion-resistant alloy, industrial experiments were conducted to sample the entire process of 8810 nickel based alloy. Scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） were used, and thermodynamic and kinetic calculations were combined to explore the characteristics and formation mechanism of large-sized inclusions. The research results indicate that the large-sized inclusions appearing in steel can be mainly divided into two types. One type is the micro inclusions of low melting point SiO₂-CaO-Al₂O₃-MgO large particles containing mass percent of SiO₂ bout 37%-45%, another type is low melting point CaO-Al₂O₃-MgO large particle micro inclusions without SiO₂. By comparing the composition of inclusions and slag, as well as calculating the size of slag inclusions using a model, it was verified that both types of inclusions were formed due to the inclusion of slag during the AOD stage steel stirring. However, during the AOD reduction period, the former was either removed or modified as CaO-Al₂O₃-MgO inclusions due to the recreation of slag and the increase of Al content. In the statistical analysis of inclusions, it is indicated that, the CaO-Al₂O₃-MgO inclusion is more severe than the SiO₂-CaO-Al₂O₃-MgO inclusion in the subsequent process, and it still exists until the casting period. Therefore, the behavior of low melting point CaO-Al₂O₃-MgO inclusions in subsequent smelting was analyzed through dynamic calculations and Thermo Calc software. The results show that the inclusions are not easy to float and remove from the appearance of AOD tapping until the end of LF hanging ladle. At the same time, it leads to the precipitation of TiN with CaO-Al₂O₃-MgO inclusions as the core during the solidification stage of mold casting, forming composite inclusions, as well as single TiN inclusions appearing during the solidification stage, which ultimately become the main types of inclusions in the ingot.

Due to its good mechanical properties and cutting performance, sulfur-containing free-cutting steel is widely used in industries such as automotive manufacturing, machinery manufacturing, and shipbuilding industry. With the development in the fields of infrastructure, passenger vehicles, and maritime transportation in recent years , the production volume and quality requirements of sulfur-containing free-cutting steel have also increased. The method of calcium treatment is usually used to regulate the inclusions in the steel. However, the sulfur-containing characteristics of sulfur-containing steel have a significant negative effect on the cleanliness and castability of the steel during the smelting and casting processes. Therefore, establishing a reasonable calcium treatment process is of great importance for improving the castability of sulfur-containing free-cutting steel. The effects of factors such as the timing of sulfur wire addition, the time interval between feeding calcium wire and sulfur wire, and the amount of calcium wire added on the cleanliness of the steel and the clogging of nozzle were systematically investigated, analyzing the main reasons for the nozzle clogging in sulfur-containing free-cutting steel. The research shows that inclusions with CaS on the surface and Al₂O₃ in the core are generated in the steel after feeding sulfur wire and calcium treatment. The continuous deposition and adhesion of these inclusions on the inner wall of the nozzle are the main cause of nozzle clogging. In steel with w （[Al]）=0.03%, when w （[S]） exceeds 0.015%, it is prone to the formation of high melting point inclusions, deteriorating the castability of the steel. For 140 t of 45S sulfur-containing free-cutting steel, feeding the sulfur wire separately after LF and RH, extending the feeding interval between calcium wire and sulfur wire to over 10 minutes, and reducing the total feeding amount of calcium wire to below 100 m can effectively reduce the quantity of CaS·Al₂O₃ inclusions in the steel. This can increase the number of continuous casting heats for 45S steel to over 15 heats. It provides a theoretical basis for optimizing the calcium treatment process of sulfur-containing free-cuttingsteel, which helps improve production efficiency and product quality. It is of great significance for promoting the application and development of sulfur-containing free-cutting steel in the fields of machinery, transportation, and other industries. Future research will focus on how to control the quantity and morphology of inclusions in sulfur-containing steel, the impact of inclusions on the quality of steel plates after rolling, and how to reduce the amount of calcium added.

The consumption of fossil energy in the steel industry intensifies environmental pressures, with the ironmaking process serving as a critical link in energy conservation and emission reduction throughout the sector. In the context of China's goals for "carbon peaking" and "carbon neutrality", the exploration and utilization of green renewable energy sources as substitutes for fossil fuels is an essential pathway for the development of the steel industry. Biomass, recognized as a green, carbon-neutral resource, possesses characteristics such as widely distributed, low pollution, and renewability. The application of biomass energy in ironmaking can significantly contribute to energy savings and emission reductions, playing a crucial role in mitigating carbon consumption in the steel industry. The distribution of biomass resources, pretreatment methods, utilization approaches, and the physical and chemical properties of biomass were systematically discussed, while the current research status of natural biomass, biomass char, and biomass derivatives was discoursed in direct iron reduction, blast furnace injection, biomass coke, biomass pellets, and biomass sintering. Firstly, it is noted that biomass can be directly added as a reactant to pellets for the reduction of biomass iron ore pellets, and that syngas generated from biomass pyrolysis and gasification can also be used for the reduction of iron ore. Furthermore, future efforts could focus on improving biomass processing methods to optimize the quality of biomass sinter and biomass pellets by enhancing raw material particle size and ratios, thereby optimizing the use of biomass for blast furnace injection or existing charge preparation processes. Given the inherent physicochemical properties of biomass, further fundamental research is necessary for its application as energy in the ironmaking process. Specifically, exploration and practical studies on the crushing strength and metallurgical properties of biomass composite iron ore raw materials developed for large blast furnaces are needed. Additionally, strengthening inter-industry collaboration to develop high-strength, highly reactive biomass composite materials suitable for blast furnace production represents one of the future research directions.

As the blast furnace production process becomes increasingly complex,the thermal conduction characteristics of the cooling wall under extreme high-temperature and high-pressure conditions are facing more stringent demands. Traditional heat conduction models can no longer meet the need for precise predictions. Therefore,fractional-order heat conduction models,which effectively describe complex media and multi-scale heat transfer phenomena,have garnered widespread attention. A review of heat transfer research on blast furnace cooling walls based on fractional-order heat conduction models is provided, aiming to offer a theoretical foundation for thermal management and prolonging the service life of cooling walls. Firstly,the mathematical basis of fractional-order heat conduction models and their associated equations are introduced,followed by an analysis of the characteristics of fractional-order equations and commonly used solution methods. Next,the heat conduction mechanisms of the blast furnace cooling wall under extreme conditions such as high temperatures and pressures are discussed in detail. A method for establishing a three-dimensional fractional-order heat conduction equation is proposed,and the framework for analyzing the heat transfer process is explored through numerical simulations and experimental validation. Finally,the current state and challenges of applying fractional-order models to the study of blast furnace cooling walls are analyzed. The potential applications of these models in the design of cooling wall materials and structures,offering future research directions,including model accuracy enhancement,optimization of computational methods,and promotion of practical engineering applications are explored. These studies provide valuable theoretical support and technical references for the thermal management and optimization design of blast furnace cooling walls.

In recent years,promoting the high-quality development of China's iron and steel industry and working to achieve the "dual-carbon" goal are the overall guiding principle of the development of China's iron and steel industry. Under this background,the characteristics of China's iron and steel industry have changed significantly. The characteristics of the iron and steel industry are described in detail,including the analyses of crude steel outputs and annual growth rates of China from 2000 to 2023. Combined with the evolution modes of crude steel output in developed countries,the phase of China's steel output is predicted. Based on the proportion of different iron and steel manufacturing processes in China from 2000 to 2023,the CO₂ emission values per year of the whole iron and steel manufacturing process is calculated,which plays the role in judging the urgency and necessity of achieving the "dual carbon" goal in China. The current situations of the iron and steel manufacturing process in major steel producing countries are used as the research object for explaining the features of ensuring the best quality of steel products and reaching the best steel manufacturing efficiency. This also can clarified the current roles and effects of various iron and steel manufacturing processes. Combined with the above analysis,the corresponding strategy of the structural adjustment of iron and steel manufacturing process in China is studied with the perspective of engineering philosophy and overall strategic thoughts. Meanwhile,the structural adjustment scheme of "BF-BOF" traditional process,"Short process of" total scrap-EAF " and" 100% hydrogen base reduction DRI-EAF " process are proposed to adapt the new iron and steel characteristics. Three critical issues in the process of iron and steel manufacturing process are discussed,including the scrap quantity for EAF steelmaking,the mathematical prediction of powder consumption during the process decarbonization and innovate ways for eliminating steel quality defects due to scrap smelting process residual elements enrichment in EAF steelmaking process. Once these issues are solved successively,it will benefit the iron and steel manufacturing process structural optimization and high quality development in China.

Sintering flue gas circulation technology has become an important technical measure for sintering machine to increase air volume and output, reduce CO, reduce air leakage, and reduce solid fuel consumption. Driven by the pollution reduction and carbon reduction policy of the iron and steel industry, increasing the flue gas circulation ratio can further strengthen the effect of pollutant emission reduction and waste heat utilization. Therefore, the high proportion of sintering flue gas circulation is an important trend of future technological development. The development and application status of flue gas circulation technology at home and abroad is systematically summarized, it is considered that sintering flue gas circulation technology has been perfect, and the main technical route should be the flue gas internal circulation scheme of high and low temperature flue gas combination. According to the different needs of sintering production, there are some differences in the selection of bellows, locations and air distribution schemes. In addition, in terms of process optimization, with the increase of flue gas circulation ratio, it should pay more attention to problems such as the decrease of oxygen volume fraction, the increase of water volume fraction, and the balance of air volume and heat. In the process of technology application, it should focus on the reliability of gas extraction, ash accumulation in pipeline, fan matching, flue gas distribution and the uniformity of the sealed hood flow field. On the basis of the research and application analysis of sintering flue gas circulation technology, the process design concept of high proportion flue gas circulation is introduced in detail, focusing on the high proportion flue gas circulation project applied by HBIS Group as an example. Through cycle process innovation, core equipment breakthrough and operation parameter optimization, HBIS Hansteel and Tangsteel New District have stably achieved a high proportion of more than 30% flue gas cycle, and achieved project promotion in 46 sintering machines. And practical experience for the implementation of high proportion flue gas circulation technology in sintering machines is provided. This is of great significance for vigorously promoting the application of sintering flue gas circulation technology and accelerating the process of pollution reduction and carbon reduction in the iron and steel industry.

Under the current "dual-carbon" framework, the high-value utilization of typical large-scale solid wastes from metallurgical processes and other major industrial sources has emerged as a critical issue demanding urgent resolution within the industry. Large-scale solid wastes from metallurgical processes, including blast furnace slag and dust ash, as well as other major industrial solid wastes such as fly ash and coal gangue, are rich in valuable resources like silicon and aluminum. Through appropriate conditioning and proportioning treatments, these solid wastes can be transformed into inorganic fiber materials exhibiting excellent thermal insulation and refractory properties, thereby achieving high-value utilization of both metallurgical and other major industrial solid wastes. The research progress in preparing mineral wool fibers is reviewed, using conditioned blast furnace slag as the raw material and silicon-aluminum-based ceramic fiber materials using dust ash in combination with fly ash or coal gangue. It analyzes the advancements in the production of inorganic fibers via the spray-blowing method and the centrifugal method from three perspectives, fundamental principles, experimental studies, and industrial practices. Pilot-scale experimental studies are conducted to produce mineral wool fibers from conditioned blast furnace slag using both spray-blowing and centrifugal methods. The results indicate that spray-blowing pressure significantly affects the content of fiber slag balls, while having minimal impact on the average fiber diameter. Specifically, increasing the spray-blowing pressure from 0.20 MPa to 0.38 MPa reduces the fiber slag ball mass fraction from 25% to 16%, with negligible changes in fiber diameter. Conversely, roller speed has little effect on fiber slag ball content but significantly influences fiber diameter; as roller speed increases, the average fiber diameter decreases from 3.17 μm to 2.73 μm. The study further compares the differences between mineral wool fibers produced by the two methods in terms of fiber diameter, fiber slag ball content, and fiber compressive strength. Additionally, it outlines the application prospects of silicon-aluminum-based inorganic fiber materials, derived from metallurgical large-scale solid wastes in conjunction with other major industrial solid wastes, in sectors such as construction, industry, aerogels, and photocatalytic materials. Building upon the existing research foundation, future research directions for the production of inorganic fiber materials from metallurgical large-scale solid wastes is proposed, aiming to further advance waste valorization, energy conservation, and carbon reduction.

Compared with sintering production, pellet production is more energy-efficient and environmentally friendly. The burden structure with high proportion of pellet is an effective way for blast furnace to achieve low carbon and green ironmaking. It is the key to realize the industrial production of fluxes pellets in blast furnace for high proportion pellet smelting. The belt roasting machine to produce fluxes pellets has great technological advantages. The three 3 000 m³ blast furnaces in Tangsteel New District designedly adopted 50%-70% pellet structure, and two 624 m² large-scale belt roasting machines were set up. In order to break the long-term technological monopoly for large-scale belt roasting machine abroad, the comprehensive research and development on the process technology and equipment of belt roasting machine was carried out in Tangsteel. Through the development of fine powder pretreatment, ore blending and roasting technology, the production technology of medium and high silicon flux pellets was mastered. With the design, manufacture and application research for the equipment localization, the localization of the core equipment of the large-scale belt roasting machine was realized to break the long-term monopoly of foreign countries. Through the development and application of intelligent technology, the efficient cooperation of pellet production line was obtained, and the production efficiency of belt roasting machine was significantly improved. Additionally, with the development and application of low energy consumption and low emission technology, the energy consumption and pollutant emission of the pelleting process were significantly reduced, the low-carbon and green production was realized. Apparently, the development and application of large-scale belt roasting machine in Tangsteel has achieved the full independent research, development and design of large-scale belt roasting machine and the localization of equipment for the first time, which has opened up a new situation for the promotion and application of belt roasting machine. To date, the production technology of flume pellets and the smelting technology of high proportion pellet in blast furnace have been mastered by Tangsteel. And these exploration and practice for burden structure in blast furnace of Tangsteel have played the good leading and demonstrative role in the popularization and application of burden structure with high proportion pellet in China.

The iron and steel industry is facing the problem of depletion of high-quality coal carbon resources and green carbon reduction, combined with the uneven distribution of coal resources in China, the large proportion of bituminous coal reserves and the global "carbon peak, carbon neutral" development background. The injection of high proportion bituminous coal can make full use of resources, alleviate the smelting cost of enterprises, and reduce the carbon emission of blast furnace smelting, which will become the mainstream trend in the future. In order to investigate the effect of high proportion bituminous coal injection on the process of blast furnace, a mathematical model of high proportion bituminous coal injection in blast furnace was established based on the production data of large blast furnace and the material balance and heat balance. Through theoretical calculation, the variation law of theoretical combustion temperature, gas content, direct reduction degree, carbon and heat distribution and carbon dioxide emission in blast furnace with the increase of bituminous coal injection ratio was analyzed. The results show that when the proportion of bituminous coal is increased by 10 percent point, the theoretical combustion temperature decreases by about 6-7 ℃, the direct reduction degree decreases by about 0.012, and the gas content in the furnace bosh increases by about 5 m³. Regional carbon, including the total carbon per ton of iron into the furnace, the carbon consumption of direct reduction of iron, the carbon consumption of desulfurization, and the carbon consumption of burning before the tuyere, all show a decreasing trend. The effect of heat distribution in the furnace is obvious. In terms of heat income, the heat release of carbon combustion decreases, the heat release of C and H elements increases, the physical heat brought by hot air decreases, and the overall heat income shows a downward trend. In terms of heat expenditure, desulfurization heat consumption decreases, coal decomposition heat increases, iron oxide decomposition heat consumption is basically unchanged, total heat expenditure is basically unchanged, and the whole furnace heat loss shows a downward trend with the increase of bituminous coal proportion. At the same time, the theoretical combustion temperature and heat loss decrease caused by the increase of bituminous coal ratio by 10 percent point, and the oxygen enrichment rate of 0.3 percent point and the coal ratio of 2.1 kg need to be increased at the same time to maintain the normal condition of the blast furnace. After blast furnace injection of high proportion bituminous coal, the carbon dioxide emission shows a decreasing trend, and the reduction of ton iron is about 3-5 m³.

With increase in the high top pressure, the BF iron-making process has obtained obvious improvement in China, and the intensified operation on BF also has been unprecedentedly increased. Apparently, this technology of intensified operation on BF with high top pressure has been widely adopted and recognized by industry. Nevertheless, the systematic theoretical research about this technology is relatively scarce currently, and the available research basically focused on the effect of high top pressure on the volume and flow rate of gas in BF. Therefore, based on the actual production, the impact mechanism of high top pressure on the smelting process of BF is systematically studied in this paper. Firstly, the effects of high top pressure on smelting intensity, lumpy zone, the pressure difference of burden columns, the distribution of gas flow and fabric, the activity of tuyere and hearth, the discharge of iron and slag, and the reaction of non ferrous elements are elaborated. Secondly, the actual level of different bosh gas index under high top pressure operation is statistically analyzed, and the revision suggestions also are proposed for the control standards of bosh gas index. It is point out that the relatively reasonable bosh gas indexes of BFs about 3 000, 2 000-3 000, and 1 000-2 000 m³ is 58-66, 58-70 and 58-85 m/min respectively. Finally, the theoretical research on high top pressure technology above has been applied and verified in the production of two 1 500 m³ BFs at Tangyin Company of Hebei Iron and Steel Group. Specifically, on the basis of successful blow-on and production, the intensified operation technologies mainly include high top pressure, large air volume, high oxygen enrichment, and low furnace temperature are used by the two BFs, as a result, the smelting of BF has been effectively strengthened, the various technical and economic indicators of BF also have been rapidly improved, and the successful application of intensified operation on BF with high top pressure has been achieved, which could provide certain reference significance and promotion value.

In recent years, the steel industry has faced increasing pressure to reduce energy consumption and emissions. It has become the development direction of many steel companies to produce high-Mn cryogenic steel by using an efficient, energy-saving, and low-cost "converter/electric furnace→refining→continuous casting" process. However, high-Mn cryogenic steel has a high manganese and carbon content, which results in poor thermal conductivity of the molten steel and a large line expansion coefficient of the solidified slab shell during cooling. This can lead to considerable thermal stresses during cooling, increasing the risk of steel leakage. In addition, the reaction（[Mn] + （SiO₂） → [Si] + （MnO）） inevitably occurs at the steel-slag interface in the mold during the casting process, which leads to the change of slag composition and properties, and deteriorates the lubrication and heat transfer control function of mold flux. During the preliminary research, it is found that domestic steel mills using the continuous casting to produce high-Mn cryogenic steel are not running successfully, with the cast slabs prone to longitudinal cracks and frequent steel leakage accidents, some mills even have difficulty in batch cast. The surface defects of the slab and frequent steel leakage accidents have seriously hindered the large-scale production of high-Mn cryogenic steel. As one of the key technologies of continuous casting, mold flux technology has an important influence on ensuring the successful production and the surface quality of slab. At present, the research of high-Mn cryogenic steel mainly focuses on composition design, rolling heat treatment, welding technology and so on. However, there is no systematic report on the research and development of special mold flux system. Therefore, the reactivity of high-Mn steel between slag and steel, the influence of MnO on the rheological characteristics of slag, and the control of heat transfer through the slag film are reviewed, and the research focus of CaO-SiO₂-MnO based low reactivity slag system is clarified. The development of low reactivity slag for high-Mn cryogenic steel has important significance, which expands and deepens the theory of heat and lubrication coordination control of mold flux for difficult-to-cast steel species, promotes the efficient, green, and low-carbon production of the defect-free slab, and is also the development direction of future special slag systems.

Magnetite concentrate is one of the commonly used sintering materials. Magnetite concentrates from different origins usually have different properties, and their addition to sintered mixed ores will inevitably have an impact on the sintering process and the quality of sintered ore. Through sinter pot tests, the sintering performance of hematite-goethite-magnetite type mixed ores and the metallurgical properties of sintered products were compared between finer-grained domestic high magnesium magnetite concentrate （DM） and coarser-grained high silicon Australian magnetite concentrate （AM）. Moreover, the effect of magnetite concentrate properties on the generation characteristics of calcium ferrite and the low-temperature reduction degradation performance of sinter products was analyzed from the perspectives of raw material properties and microstructure of sinter products. The results indicated that, as the proportion of AM replacing DM increased from 0 to 30%, tumble index of sinter products decreased from 59.87% to 57.35%, yield decreased from 63.69% to 60.92%, productivity decreased from 1.49 t/（m²·h） to 1.30 t/（m²·h）, solid fuel consumption increased from 76.62 kg/t to 78.86 kg/t, reduction index I_R decreased from 86.64% to 83.08%, and the low-temperature reduction degradation index I_RD>3.15mm decreased from 68.69% to 49.40%. From the perspective of mineralogy of sinter products, as the proportion of AM replacing DM increased, the content of composite calcium ferrite in sinter products significantly decreased, and the crystallization and development situation deteriorated, transitioning from needle shaped to short columnar or plate-like. Meanwhile, the amount of silicate glass phase and irregular skeletal hematite increased. The reason for this was that DM with finer particle size has higher self-fluxing and better oxidation properties than high silicon AM with coarser particle size, which was conducive to the formation of primary melting phase, promoting the assimilation of nuclear particles, and forming a bonding phase with high bonding strength.

Two types of turbulence inhibitors, namely cylindrical turbulence inhibitor and impact pad, were used in a 6-strand tundish with side-arranged inlet of a steelmaking plant. In order to evaluate the metallurgical effect of the two types of tundish during the ladle changeover process, the flow field distribution of the two type of tundishes and the slag entrapment situation in the water model, evolution of inclusions during the ladle changeover process were studied by industrial sampling, physical model, and numerical simulation methods. Particle image velocimetry （PIV） was applied to measure the flow field distribution and velocities at the water oil interface. The morphology, size, and composition of inclusions in the two type of tundishes during the ladle changeover process were explored by industrial sampling and Scanning Electron Microscopy-Energy Dispersion Spectrometer （SEM-EDS）. The results show that the velocity spatial distribution inside the tundish is uneven, with higher velocity in the impact zone and lower velocity at the edge strand. There is an upward backflow in the tundish with a cylindrical turbulence inhibitor. At a normal casting rate of 2.65 t/min, the maximum fluid velocity at the water oil interface of both types of tundish is around 50 mm/s, indicating a relatively stable water oil interface. When rapidly refilling （5 t/min） after ladle change, a circulation is formed near the wall in the impact zone of the tundish with a cylindrical turbulence inhibitor, and a strong horizontal flow that paralleling to the liquid surface towards the outlet is formed. The maximum velocity at the water oil interface is 285.16 mm/s, and the slag eye area is 735.42 cm². A large number of large-sized oil droplets are entrained in the impact zone. For the tundish with an impact pad, the impact zone forms an upward flow field along the wall, with a maximum velocity of 186.54 mm/s at the water oil interface and a slag eye area of 399.27 cm². Small oil droplets are entrained in the impact zone, forming a water oil mixture. The sampling results before and after the ladle change show that no large-sized （≥50 μm） inclusions are found in both types of tundish at the end of casting of the previous heat. After the liquid level rise to the normal working level, a large-sized inclusion with a size of 240.32 μm is found in the tundish with a cylindrical turbulence inhibitor. The average size of the inclusion increases from 13.18 μm to 29.88 μm, and the proportion of large-sized （≥50 μm） inclusions is 24%. The mass fraction of CaO in the inclusion increases significantly. However, no inclusions with a size larger than 100 μm are found in the tundish with an impact pad, and the average size of inclusions remains basically unchanged. The proportion of large-sized （≥50 μm） inclusions is 6.7%. Overall, the metallurgical effect of the impact pad is superior to that of the cylindrical turbulence inhibitor.

With the rapid development of oil and gas industry, the requirements for the strength, toughness and weldability of pipeline steel are constantly increasing. Optimizing the argon sealing process during continuous casting is crucial for reducing or avoiding internal defects caused by argon bubbles, which is of great significance for improving the quality of pipeline steel products. L485M pipeline steel was taken as the research object, the effect of the sealed argon flow rate of the submerged entry nozzle on the internal defects of the pipeline steel L485M was studied by controlling the sealed argon flow rate and the casting speed. Then optimized the argon flow rate and casting speed to solve the internal defects of the slab caused by the argon bubble. The results show that,the argon bubble is generated when the flow rate is too high, which is easily captured by the solidification front of the slab and leads to the internal defects of the slab, formed elliptical flattened defects after rolling, distributed near the surface of the steel plate; An increase in argon sealing gas flow rate or casting speed will both lead to a higher occurrence rate of steel plate defects. Reasonable argon flow rate and casting speed of continuous casting machine are important parameters to ensure that bubbles can float up in time and not enter the slab. The reasonable casting speed of L485M pipeline steel slab with a specification of 260 mm×2 070 mm is 0. 75m/min, and the argon flow rate of split nozzle should not be greater than 2.5 L/min. The integral nozzle can effectively avoid the internal defects caused by argon bubble. The research results are of great significance for improving the theoretical process of argon sealing in the continuous casting of pipeline steel and enhancing the quality of pipeline steel products. They also provide reference value for the optimization of the submerged entry nozzle sealing process for other steel grades, the effect of continuous casting speed on internal defects caused by argon bubbles in slab, and the behavior of argon bubbles in the protective continuous casting process.

The thermodynamic characteristics, reaction mechanisms, and the impact of temperature and time on the reduction process of hematite （Fe₂O₃） by ammonia （NH₃） were to be explored. The standard Gibbs free energy of the reduction reactions between Fe₂O₃ and Fe₂SiO₄ with NH₃, H₂, and CO was calculated using HSC Chemistry 6.0 software to assess the feasibility of NH₃ as a reducing agent. The horizontal high-temperature furnace was used to heat and reduce hematite, with the reduction effects investigated under various temperature and time conditions with NH₃. The results show that NH₃ can effectively reduce Fe₂O₃ at 290 ℃, while H₂ requires a higher temperature of 542 ℃, indicating that NH₃ has a reduction advantage at lower temperatures. The thermodynamic reaction temperature for NH₃ reduction of Fe₂SiO₄ is 480 ℃, in contrast, CO and H₂ are not spontaneous at this temperature, demonstrating the thermodynamic advantage of NH₃ in reducing Fe₂SiO₄. As the temperature increases, the weight loss and reduction rates of hematite increase, and hematite can be completely reduced by NH₃ with the volume fraction of 30% at 900 ℃. The extension of reduction time also leads to an increase in weight loss and reduction rates, with 90% reduction rate achieved in 60 min and 100% reduction rate in 180 min. Characterization of the reduced samples by XRD, SEM, and OM reveals that Fe₂O₃ is first converted to Fe₃O₄, then rapidly to FeO, and finally FeO is converted to pure iron （Fe）. EDS spectral analysis shows that as the reaction proceeds, the content of O atoms decreases while the content of Fe atoms increases, ultimately achieving the complete reduction of Fe₂O₃ to pure Fe. During the NH₃ reduction of Fe₂O₃, the number of N atoms first increases and then decreases, indicating that Fe is nitrided by NH₃ to form Fe₄N, which then decomposes at high temperatures to produce Fe and N₂. NH₃ shows a significant thermodynamic advantage in the reduction of hematite, and the reduction process can be divided into several stages, initial slow conversion, rapid reaction in the middle, and a decrease in reaction rate in the later stage due to product coverage. The entire process is completed within 30 min, ultimately achieving the complete conversion of Fe₂O₃ to pure Fe. Theoretical basis and experimental data support are provided for the industrial use of NH₃ to reduce hematite.

The bosh, belly and lower part of the shaft the furnace body area is one of the limitations of efficient and longevity operation of the blast furnace, the formation of a stable slag crust is the key to ensuring the safety of the cooling stave operation in this area. In order to explore the essential characteristics of slag crust, firstly, the slag crust samples were obtained from the bosh, belly and lower part of the shaft through the anatomy and the investigation of cooling stave breakage in several blast furnaces. Secondly, the phase composition and microstructure evolution of the slag crust were studied through analysis methods such as XRF, XRD, and SEM-EDS. Based on the compositional characteristics of slag crust, a category system of slag crust was established, focusing on comparing the phase and morphological characteristics of cooling stave slag crust of blast furnace with different volumes and different cooling stave materials. Finally, the cooling stave slag crust regulation measures were formulated. The results show that the cooling stave slag crust can be mainly divided into two categories, the slag crust mainly composed of slag-iron and the harmful element binder mainly composed of ZnO and carbon. Among them, harmful element binders have poor thermal stability and are prone to detachment, which is not conducive to the safe operation of the cooling stave. The basicity of the slag in the slag crust first increases and then decreases with the decrease of height. The composition of cooling stave slag crust of blast furnace with different capacity under the same cooling stave material does not differ much, while the difference of slag crust of blast furnace body with different cooling stave materials is large. The copper stave slag crust has a clear layered structure, and its slag composition shows the characteristics of high aluminum and low magnesium slag system, the main precipitation phase is Ca₂Al₂SiO₇. While the cast iron stave slag crust has no layered structure, the content of Al₂O₃ and MgO is slightly lower than that of blast furnace slag, and its main precipitation phase is Ca₃MgSi₂O₈. Finally, it is clarified that the formation and control of slag crust should be carried out from the aspects of edge gas flow temperature and slag composition, in order to ensure the crystallization kinetics conditions of slag hanging on the surface of the cooling stave and provide a theoretical basis for the long-term operation of the cooling stave of the blast furnace.

The medium carbon micro-alloyed steel containing niobium is crack-sensitive steel, which is easy to crack in the continuous casting process and seriously deteriorates the surface quality of the bloom. The causes of corner cracks in 46MnVNbS5 steel were analyzed using an optical microscope, scanning electron microscope with energy dispersive spectrometer, three-dimensional etching technology, high temperature confocal laser scanning microscope and Thermo-Calc software. The surface crack distribution of 320 mm×425 mm casting bloom was observed, and no obvious cracks were found in the range of 0-20 mm of the inner arc, and only pitted defects were observed on the samples 20 mm away from the inner arc. There are obvious cracks in the range of 20-40 mm, and the crack size is generally greater than 10 mm. At the distance of 25 mm from the inner arc surface, cracks were observed only at the low multiplier surface. At 30 mm, 35 mm, and 40 mm from the inner arc surface, there were cracks on multiple observation surfaces of the sample. The crack grows along the dendrite growth direction. A large number of coupling precipitates of manganese sulfide and carbonitride in and near cracks were determined by SEM-EDS. The surface of the crack specimen was corroded and it was found that the crack spread along the ferrite film. The thermodynamic results show that manganese sulfide is the main inclusion in the solid-liquid zone of steel. The niobium-rich carbonitride and vanadium-rich carbonitride will be precipitated successively, which is consistent with the types of inclusions obtained by experiments. The cracking zone （620.1-794.3 ℃） of steel containing niobium was determined by high-temperature confocal laser microscopy, and numerical simulation was applied to simulate the corner temperature field of continuous casting bloom, and the cooling system was optimized to avoid the cracking zone of medium carbon micro-alloyed steel containing niobium. This study provides the methods to solve the crack of casting bloom and has important practical significance.

To study the effect of w（（CaO））/ w（（Al₂O₃）） in the refining slag on the molten steel during the secondary refining process, the w（（CaO））/ w（（Al₂O₃）） was adjusted through industrial trial. The change of the sulfur content in steel was analyzed. The results shows that the desulfurization ability of the refining slag with the w（（CaO））/ w（（Al₂O₃）） of 2.0 is better than that of refining slag with the w（（CaO））/ w（（Al₂O₃）） of 1.6. The melting temperature, solid phase fraction, viscosity, and sulfide capacity of the refining slag with different w（（CaO））/ w（（Al₂O₃）） are calculated. When the w（（CaO））/ w（（Al₂O₃）） in the refining slag exceeded 1.8, the refining slag transitions from the liquid phase to a semi-liquid phase, and the solid phase fraction of the refining slag increases continuously at 1 873 K. The influence of viscosity kinetic factor on the desulfurization ability of slag was considered. A dimensionless desulfurization index of S_index was proposed to represent the desulfurization ability of the refining slag. It is revealed that with the increase of w（（CaO））/ w（（Al₂O₃）） in the refining slag, the viscosity of the slag first decreases and then increases. When the w（（CaO））/ w（（Al₂O₃）） is 1.8, the viscosity η reaches a lowest level. With the increase of w（（CaO））/ w（（Al₂O₃）） in the refining slag, the sulfur capacity C_s gradually increases. With the increase of w（（CaO））/ w（（Al₂O₃）） in the refining slag, the value of S_index first increases and then decreases. When the w（（CaO））/w（（Al₂O₃））of the slag is 2.0, the value of S_index reaches a highest level. It is suggested that control the w（（CaO））/w（（Al₂O₃）） of the slag within the 1.8 to 2.0 is more beneficial for improving the desulfurization ability of the slag. Finally, the S_index of CaO-Al₂O₃-SiO₂-5.68%MgO refining slag at 1 600 ℃ was calculated. In the liquid region of the refining slag, the S_index increases with a higher w（（CaO））/ w（（Al₂O₃）） in the refining slag, which is beneficial to improve the desulfurization efficiency of the molten steel.

The smelting tasks at blowing stage in converter vanadium extraction process are different,and the composition and temperature of the molten pool are constantly changing,which makes the working conditions such as oxygen supply lance position and flow rate change at different stages of smelting,resulting in different stirring characteristics of the molten pool at different stages of blowing. The stirring energy model of converter molten pool was established,and the effects of temperature,oxygen supply flow and bottom blowing on the stirring energy of molten pool in different blowing stages were studied. It is found that the energy density of top blowing stirring in each stage of converter vanadium extraction process is significantly smaller than that of bottom blowing stirring,and the CO bubble stirring energy generated by chemical reaction only accounts for 0.41%-1.74%. With the smelting process,the top blowing stirring energy density decreases from 165.30 W/t to 144.63 W/t,and then gradually increases to 192.84 W/t. The stirring energy density produces by CO bubbles is up to 15.21 W/t. The stirring energy density produced by bottom blowing nitrogen gradually increases from 786.92 W/t to 865.57 W/t. In the smelting process,the stirring energy of the molten pool is reasonably increased by changing the top blowing lance position and bottom blowing flow rate at different stages,and the carbon loss can be effectively reduced. On this basis,the effects of different Mach number,oxygen flow rate,lance position and bottom blowing intensity on the impact characteristics and mixing time of molten pool were studied by 1∶3 water model experiment. With the progress of blowing,the impact depth of the molten pool is 61-90 mm under the condition of Mach number of 1.97,and the impact range of the molten pool is 19.93%-29.41%. The change degree of impact diameter is 37.41%-42.54%. The longest mixing time is 54 s and the shortest is 39 s. The process system of vanadium extraction from converter is optimized. In addition,when the bottom blowing intensity is greater than 0.09 m³/（min·t）,the mixing time of the molten pool is significantly reduced. When the bottom blowing intensity reaches 0.12 m³/（min·t）,the stirring intensity of the molten pool decreases. When the bottom blowing flow rate increases to 0.15 m³/（min·t）,the mixing time of the molten pool reaches a minimum of 27 s. In order to reduce the mixing time of the molten pool,the bottom blowing intensity can be appropriately increased to improve the efficiency of vanadium extraction. It is beneficial to achieve vanadium extraction and carbon conservation in the converter by adjusting the lance position and gas supply intensity at different stages of vanadium extraction and blowing,and reasonably controlling the stirring characteristics of the molten pool.

30Cr15Mo1N is a kind of strength martensitic stainless steel with nitrogen mass fraction of 0.4%, the important problem in its application is the matching of high hardness and high corrosion resistance. The microstructure and corrosion resistance of 30Cr15Mo1N steel after tempering with different temperatures were studied by SEM, TEM, chemical precipitates analysis and salt spray test. The results show that the microstructure after quenching, cryogenic treatment and tempering with temperature below 500 ℃ is distributed of micrometer undissolved precipitates and nanometer newly precipitated precipitates on the lath martensite matrix. With the increase of tempering temperature, the types of precipitates remain unchanged, which are M₂₃C₆ and Cr₂（C,N） types, and the number and size of precipitates increase gradually. In particular, when tempering at 475 ℃, the precipitated phase mass fraction suddenly increases, the martensite gradually dissolves and the tempering sorbite occurs when tempering temperature is higher than 500 ℃. At 500 ℃, the peak hardness of secondary hardening is 60.7HRC. With the increase of tempering temperature, the strengthening effects of martensite and solid solution gradually decrease, and the secondary hardening effect mainly comes from the strengthening effect of a large amount of precipitated phases. The salt spray test results show that small pitting corrosion is the main feature when the tempering temperature below 400 ℃, and visible corrosion occurs after tempering at 450 ℃. When the tempering temperature is no less than 450 ℃, granular and lamellar corrosion products are deposited on the specimen surface. The samples tempered at 475-500 ℃ have the most serious corrosion, and the corrosion resistance deteriorates as the tempering temperature increases. During the tempering process, the precipitation of Cr containing precipitates leads to Cr-depletion zone in the surrounding matrix, which leads to the decline of corrosion resistance. When the tempering temperature reaches 600 ℃, the distance between the Cr depletion on the edge of the precipitates increases, and the corrosion resistance is slightly improved. Therefore, if high hardness and high corrosion resistance coexist, meet the hardness requirements of bearings no less than 58HRC, tempering temperature should not be higher than 400 ℃.

Reasonable operation of the furnace type is the key to its long life, stable operation, and sound economic and technical indicators for the blast furnace. Based on the production data of a certain steel plant's blast furnace, the blast furnace type optimization method was studied, providing scientific guidance for blast furnace operation. First, the Isolation Forest and Boxplot methods were adopted to identify and process noise in the data, and then Principal Component Analysis （PCA） was used for dimensionality reduction to eliminate noise and data redundancy, providing a high-quality data foundation for subsequent cluster analysis. Next, the application effects of two clustering algorithms, K-means and DBSCAN, were compared. The K-means algorithm achieved the best silhouette coefficient when the number of clusters was 14, indicating that the blast furnace type could be divided into 14 categories; the DBSCAN algorithm exhibited a lower Davies-Bouldin Index（DBI） when Neighborhood Radius （E_ps） and Minimum Neighborhood Sample Count（min_samples） were 6.25 and 2, showing the best clustering effect and the ability to effectively identify clusters of any shape, especially suitable for handling the complexity and nonlinearity of blast furnace production data. To evaluate the advantages and disadvantages of different furnace types, an evaluation method for operating furnace types based on comprehensive production indicators was established, selecting coke ratio, fuel ratio, output, and iron loss as key performance indicators and assigning different weights. The results show that the fourth type of furnace type performs the best in terms of blast furnace operation indicators and can be used as the operating target for a reasonable furnace type. To achieve blast furnace type optimization, the implicit relationship between blast furnace operating parameters and furnace types was explored using the Random Forest method, determining the key feature parameters that affect furnace types, including burden matrix parameters, permeability index, gas utilization rate, and standard wind speed. By analyzing the evolution of furnace types and the trend of blast furnace parameters, it is found that the deterioration of furnace types is mainly related to the decrease in permeability, which leads to uneven airflow distribution, reduces gas utilization rate, and increases pressure drop. A new method for optimizing blast furnace type management is established, providing valuable data analysis and operational guidance for on-site personnel, helping to improve blast furnace operation level, reduce energy consumption and costs, and achieve long life, stable operation, and efficient production of blast furnaces.

Ultra-high strength stainless steel is widely used in aviation, aerospace and other fields because of its good comprehensive performance. A new type of 2.1 GPa grade ultra-high strength stainless steel was taken as the research object, and the influence law of different solid solution temperature and aging treatment on the mechanical properties of steel was investigated. Scanning electron microscope （SEM）, X-ray diffractometer （XRD）, transmission electron microscope （TEM） and other means were used to characterize the microstructures of the steel in solid solution and aging state, and an intrinsic correlation was established between the heat treatment-mechanical properties-microstructure. The results show that the solid solution organization of the steel is slat martensite + residual austenite, the size of the original austenite grain increases with the increase of solid solution temperature, the strength shows a decreasing trend with increasing of solid solution temperature, while the impact absorption work increases firstly and then decreases. The strength of the solid solution by 1 050 ℃ is the highest, but due to the un-dissolved M₆C phase disrupts the continuity of matrix organization resulting in low impact absorption work, the strength and the impact absorption work of solid solution by 1 100 ℃ are lower than the 1 080 ℃ solid solution. Although the former high austenite content is conducive to improving toughness, coarse grains lead to a reduction in the impact absorption work. After aging, the strength of the steel significantly improved, 1 050 ℃ solid solution + aging has the lowest strength, while 1 080 ℃ solid solution+aging has the highest strength, the tensile strength is 2 161 MPa and yield strength is 1 784 MPa. Plastic toughness also better than 1 050 ℃ and 1 100 ℃, 1 080 ℃ impact absorption work is 37.5 J, which has the best toughness match, and there are a large number of small, diffuse Laves phase and M₂C phase precipitated in the slat martensite, which is the main reason for obtaining ultra-high strength. In the martensite slat boundary, the thin film austenite is the key to maintain good toughness. The research steel grade is the highest strength level of stainless steel in the international arena currently, and the research results can provide data support to enhance the maturity of its engineering technology.

The evolution of microstructure and cementite in the process of cold-drawing pearlitic steel wire has an important effect on the properties of the completed steel wire. The SEM, TEM, physicochemical phase analysis and APT were used to study the organization evolution and carbide evolution behavior of 82B-V pearlitic wire rods during the drawing to produce steel wires and strands. The microstructure results show that after the cold drawing process, the pearlitic lamellae gradually turns to drawing direction, and the lamellae spacing decreases from 140 nm to 80 nm, showing good deformation ability. During drawing process, a large number of dislocated cellular structures are generated within the ferrite in the steel wire. As a result, the ferrite lamellae becomes partitioned by dislocation walls, exhibiting a distinctive "bamboo" morphology. The cementite rotates and part of cementite phases between the regions of neighboring ferrite lamellae dissolve and disappear. The results of physicochemical phase analysis show that after drawing of wire rod into steel wire, element C in the alloy cementite diffused into the ferrite and a part of cementite dissolves, resulting in a reduction of the mass fraction from 7.99% to 6.67%. The content of alloy cementite in the stabilized strand is slightly recovered and increased to 7.00%; and the results of APT show that, compared with the wire rod, the average concentration of C atoms in the cementite of steel strand is only 13.5%, reduced by 7.5 percent point. The average concentration of Cr, Mn and V atoms in the strand cementite is 0.51%, 1.59% and 0.23%, which decreases by 0.246, 0.785 and 0.170 percent point, respectively, which further confirms that the dissolution of alloy cementite occurred in the process of large deformation and drawing and the diffusion of C, Cr, Mn and V into the ferrite. Through the tensile experiments and fracture morphology analysis, steel wire in the tensile process without necking produced, the fracture shows shot and crystalline, there is a tear prism through the entire cross-section. While the steel strand produced necking, the fracture is a gray lusterless fibrous, the heart of the tear prism is shallower, and the crystalline morphology is significantly reduced the strand showed better overall mechanical properties, showing a better overall mechanical properties, its tensile strength and section shrinkage reaches 2 045 MPa and 35.2%, respectively.

In order to realize the efficient treatment and resource utilization of steel slag, it aims to use blast furnace slag as a "modifier" to modify high basicity steel slag,improve the physical properties of steel slag, optimize the mineral composition of steel slag,and reveal the influence mechanism of slag microstructure on viscosity. The experimental raw materials and modified slag were analyzed by high temperature physical property tester,X-ray diffractometer（XRD）,scanning electron microscope（SEM-EDS）and Raman spectroscopy（Raman）. The results show that with the increase of the basicity（1.6-2.4）of the mixed slag,the melting temperature decreases first and then increases. When the basicity is 2.0,the high-temperature physical properties are the best. At this time,the proportion of blast furnace slag is 35.19%（mass fraction）,the melting temperature is 1 383.30 ℃,the melting time is 1.05 s,and the viscosity（temperature more than 1 405 ℃） is lower than 0.25 Pa·s.The homogeneous reaction effect is good,and the structure of each mineral is clear and evenly distributed. It is mainly composed of gehlenite（Ca₂Al₂SiO₇）,magnesium pyroxene（Ca₃MgSi₂O₈）, cementitious minerals dicalcium silicate（Ca₂SiO₄）and tricalcium aluminate（Ca₃Al₂O₆）,which realizes calcium stabilization and enrichment of cementitious materials. In addition,with the increase of basicity from 1.6 to 2.0,the high polymerization degree units in the slag microstructure undergoes a depolymerization reaction,and the relative content of the low polymerization degree unit QSi0 increases,which simplifies the microstructure and reduces the polymerization degree parameter n（BO/T）_e（the average number of bridging oxygen per tetrahedron in the network structure）to a minimum value of 0.87.When the basicity increases from 2.0 to 2.4,the role of [AlO4] in network construction is enhanced,the number of high polymerization degree units QAl3 and QAl4 increases,and the n（BO/T）_e value increases to 1.69. The calculated value of n（BO/T）_e is in good agreement with the experimental results of viscosity. This study can provide reference for the research on the viscosity of blast furnace slag quenched and tempered steel slag,the optimization of the phase composition and structure of steel slag,and is expected to promote the resource utilization of iron and steel solid waste（blast furnace slag,steel slag）.

Vanadium-titanium magnetite is a characteristic mineral resource rich in iron, vanadium and titanium, which has high comprehensive utilization value. Due to isomorphism and micro-particle embedding, it is difficult to achieve efficient separation and comprehensive utilization of iron and titanium. Based on the mineralogical characteristics and thermodynamic calculation of vanadium-titanium magnetite, a new method of "hydrogen reduction-titanium-rich separation" is proposed to realize titanium-iron separation. Through asynchronous reduction of iron oxide and titanium-iron oxide, iron oxide is transformed into metal Fe, while titanium-iron oxide is basically not reduced, and iron minerals and ilmenite are separated efficiently due to obvious magnetic differences. Under the experimental conditions, with the increase of reduction temperature and time, the recovery rate of titanium decreases and the recovery rate of iron increases. The high reduction temperature and long reduction time are not conducive to the simultaneous separation of ferrotitanium and titanium. Under the conditions of reduction temperature of 900 ℃, reduction time of 50 min, reduction atmosphere of 30%H₂+70%Ar（volume percent）, and magnetic field intensity inductance of 0.8 A, iron concentrate with TFe grade of 78.32% and recovery of 98.12% and titanium-rich ore with Ti grade of 20.92% and recovery of 33.11% can be obtained. The results of chemical composition analysis, X-ray diffraction （XRD） analysis and optical microscope analysis all show that ilmenite is effectively separated from iron minerals,titanium is effectively enriched in perovskite-rich ore. Finally, the comprehensive utilization of magnetic separation products is prospected. On the one hand, iron concentrate can be produced by blast furnace or direct reduction process to provide raw materials, which can not only reduce production cost and iron loss, but also shorten smelting cycle. On the other hand, high value-added FeTi30 alloy can be prepared from titanium-rich ore, and the theoretical calculation meets the requirements. This provides an important research direction for realizing the comprehensive utilization of products after hydrogen reduction-titanium-rich separation treatment of vanadium-titanium magnetite resources.

At present, the classical K-M（Koistinen-Marburger） model is commonly used to describe the martensite transformation kinetics in steel, but the accuracy of the model is closely related to the composition of the steel. Based on quenching experiments with different cooling rates, the martensite transformation kinetics of common medium-carbon high-silicon quenching-partitioning（Q&P） steels were studied by expansion method and metallography method. Meanwhile, an improved martensite transformation kinetic model suitable for medium-carbon high-silicon Q&P steels was established based on the traditional K-M model and verified. The results show that under different cooling rates, the martensite transformation kinetic curves of medium-carbon high-silicon Q&P steel are "S" shape, not "C" type. The phase transformation process is divided into the acceleration period at the beginning, the high-speed period in the middle, and the deceleration period in the end, which may be caused by the self-tempering phenomenon of martensite. In addition, the martensite formed near the martensite start temperature is relatively coarse, and carbon atoms diffuse from the supersaturated martensite to the surrounding unconverted austenite at the relative high temperature. The carbon enrichment of austenite increases the stability of remaining austenite, and the supercooling degree for the further martensite transformation needs to be further increased, thus reducing the martensite start temperature of the remaining austenite. The equation of martensite transformation kinetics index β is a constant of 1-2. The sensitivity of β value to quenching temperature depends on the carbon content of steel. When the carbon content increases, the sensitivity of β value to quenching temperature decreases significantly and can be basically ignored. The rate parameter α is a cubic polynomial function of the quenching temperature. With the increase of cooling rate, the rate parameter α gradually decreases, indicating that the martensitic transformation may be a time-dependent phase transformation. The equation index β gradually increases with cooling rate, which is related to the suppression of austenite plastic accommodation on martensite transformation. Considering the instantaneous dynamics of martensite transformation, the improved K-M model has a better match with the experimental data than the traditional K-M model.

The size and morphology of sulfides are important for both machinability and mechanical properties of free-cutting steels. In order to improve the level of sulfide control, characteristics （length, aspect ratio and area） of sulfide in Ca treated free-cutting steel before and after hot rolling were analyzed systematically by scanning electron microscope equipped with an automatic inclusion analyzing system. There were two kinds of sulfides in Ca treated free-cutting steel, pure MnS and CaS-MnS. The proportion of CaS-MnS was 13%-21%, and the core was an oxide. The energy spectrum distribution indicated that CaS-MnS was a solid solution phase with uniform composition. For pure MnS, the average and maximum aspect ratios in continuous casting billets were 2.191 and 26.87, respectively. After hot rolling, the average and maximum aspect ratios of pure MnS were 4.583 and 60.83, respectively. The average aspect ratio increased by 107.12%. For CaS-MnS, the length, aspect ratio and area in continuous casting billets were significantly smaller than that of pure MnS. After hot rolling, the deformation of CaS-MnS was slight, with an average aspect ratio of 1.598 and a maximum aspect ratio of 14.42, respectively. The average aspect ratio increased by 8.48%. The area had a significant impact on the deformation of pure MnS. For MnS with area no more than 30 μm², the aspect ratios in both continuous casting billet and hot rolled rod were relatively small （<4）. For MnS with area larger than 30 μm², the aspect ratio significantly increased after hot rolling. The formation mechanism of sulfides was explained. The inclusions after Ca treatment were CaO-Al₂O₃. After sulfur addition, CaO was transformed into CaS because the S content in the steel was much higher than that of O content. CaS and MnS had mutual solubility, which can promote the heterogeneous nucleation of MnS and form fine CaS-MnS. At the end of solidification, the supersaturation of Mn and S increased sharply, which makes a large amount of MnS to precipitate in a short period of time. It helps to better understand the effect of Ca treatment on sulfur-containing free cutting steels and provides guidance for engineering applications.

The nickel in 40CrNiMo steel is mainly used to improve low-temperature toughness, but the price of nickel is expensive and does not meet the requirement of low cost. A low cost CrNiMo steel with a mass fraction of 0.08% vanadium microalloyed and nickel content of only 0.3% was developed to replace 40CrNiMo steel （the mass fraction of nickel was about 1.5%）. The differences of matrix and carbide between test steels were studied by means of SEM, EBSD, TEM and XRD. The tensile test and -40 ℃ impact test were taken to compare the toughness of test steels under the same strength（10.9 grade）. The results show that the prior austenite grain size of 40CrNiMo steel is smaller than that of developed steel, which is （14.5±5.3） μm and （20.6±7.1） μm respectively. The large angle grain boundary density of 40CrNiMo is 0.7/μm high than that of the developed steel due to the fine grain size. Due to the tempering resistance improving effect of vanadium, the tempering temperature of the developed steel is increased by 60 ℃ compared with 40CrNiMo steel at the same tensile strength, and the recovery degree of the matrix is improved, thus obtaining a higher proportion of large angle grain boundary and a lower dislocation density. The dislocation density of the two test steels is 9.3×10¹⁴/m² and 2.3×10¹⁵/m², respectively. The MC, M₂C and M₃C carbides are precipitated in the developed steel microstructure after tempering. The MC carbides are spherical with diameter less than 20 nm, while the M₂C and M₃C carbides are ellipsoidal with maximum length less than 150 nm. The M₂C and M₃C carbides are precipitated in 40CrNiMo steel. The M₂C carbides are ellipsoidal with maximum length of less than 100 nm, and the M₃C carbides are strips with length of more than 500 nm. Through the statistics of maximum size of all carbide in observation fields, it is found that the proportion of M₃C cementite in developed steel is lower, and the overall size of carbides is smaller. Although the prior austenite grain size of the developed steel is large and its large angle grain boundary density is low, but its sufficient recovery and fine spherical carbide particles got after tempering improve its low-temperature toughness. When the tensile strength is about 10.9 grade, the impact absorb energy of the developed steel reaches 86 J at -40 ℃, which is higher than 74 J of the 40CrNiMo steel.

RIST A continuously studied the non-ideal operating lines of blast furnaces from his initial laboratory research to his later theoretical research. He believed that the non-ideal operating line was due to the fact that the residence time t_s of the charge in the furnace was shortened and couldn't reach the critical residence time t_s^* of the ideal reduction state, so that the operating line in the Rist diagram was pushed away from the blast furnace efficiency R point by the envelope curve. Firstly, based on the basic theory of blast furnace ironmaking and the production practices of blast furnaces, the authors of this paper try to make the link between the five parameters, which are used to evaluate the production efficiency of blast furnaces with Rist diagram in terms of mathematical relations. The residence time t_s of the charge in furnace is replaced by t_g of the gas in furnace, and then, the relationship among t_g, the bosh gas volume index χ_BG, the bosh gas volume V_BG and bosh gas volume per ton of hot metal $v_{\mathrm{O}_{2}}$ is shown. The relationship between t_g and R point of gas residence time is very complicated, which needs a large number of actual measurement data of the process in the blast furnace and can be determined by mathematical model and computer calculation. However, there are few researches in this field, and there are still many difficulties in its application in production practice. Secondly, in order to solve the operation problem in the actual non-ideal state conveniently and quickly, a method to calculate the envelope curve is suggested based on the operation data of blast furnaces. Since R point is significantly related to the gas utilization rate η_CO, the position of R point can be determined by the level of the gas utilization rate η_CO. During the on-site calculation of blast furnaces, the Rist operating line is often determined by the gas utilization rate η_CO and the tuyere oxygen consumption per ton iron $v_{\mathrm{O}_{2}}$. Therefore, the change of the gas utilization rate η_CO, which determines the change of the operation line, can be obtained by the change of the tuyere oxygen consumption per ton iron $\mathcal{U}_{\mathcal{O}_2}$ according to the method of analyzing production data. It also can obtain the characteristics and the change of the envelope curve in the Rist diagrams. The change of important parameters of the Rist model in actual production can predict the change of blast furnace condition.