The direct reduction of gas based on shaft furnace has the characteristics of high hydrogen enrichment rate, short process and small environmental pollution, which is an important way to reduce carbon emission of iron and steel metallurgy by "replacing carbon with hydrogen". With the reduction gas source changing from natural gas to coke oven gas, coal to gas, chemical by-product H₂, etc., more gray hydrogen, blue hydrogen, green hydrogen preparation technology has laid the foundation for the global development of gas-based direct reduction. Based on the current situation of resources in China, the reduction process of iron oxide in hydrogen metallurgy technology of coke oven gas zero reforming shaft furnace is analyzed, and the change of pellet performance in the reduction process of gas-based shaft furnace is summarized in combination with the research status at home and abroad. The operating state of shaft furnace is analyzed, and the influence of different reducing gas composition on the reduction thermodynamics, dynamics, reduction performance and operating state of shaft furnace are grasped. It is found that lower gas pressure and higher temperature are beneficial to the reduction of iron oxide under zero reforming process of coke oven gas. Appropriately increasing the φ(H₂)/φ(CO) in the reduction gas is helpful to reduce the reduction expansion of pellets rate and improve the compression resistance and high temperature thermal bonding performance of pellets during the reduction process. However, the reduction process is affected by many factors, and the reduction rate is not simply proportional to the H₂ content in the reduction gas. Combined with the influence of reduction gas composition on the flow distribution, temperature distribution, pressure distribution and other operating states of the shaft furnace, it is found that the temperature system and operating pressure need to be adjusted while regulating the gas composition. Reasonable gas composition not only needs to consider the reduction rate of iron oxides, but also needs to consider the reduction performance of pellets and the operation state of shaft furnace. The summarized results provide a theoretical basis for the implementation of gas-based shaft furnaces in China.

With the continuous increase in China′s steel production, the steel industry is facing severe resource and environmental problems, especially in the treatment and utilization of steel slag. In the current steel slag treatment process, a significant amount of thermal energy from steel slag is wasted, and the process of recovering metallic iron is highly energy-intensive. Additionally, the comprehensive utilization rate of tail slag is low, with most steel slag being landfilled or stockpiled. In the context of the "carbon peaking" and "carbon neutrality" targets, the development of low-carbon and green technologies for steel slag treatment and utilization is imperative. The current mainstream processes for steel slag treatment are summarized, and the advantages and disadvantages of different methods are discussed. The main pathways for resource utilization of steel slag are concluded, and the technologies for comprehensive utilization of steel slag in recent years are analyzed. Considering the current state of steel slag treatment and utilization, the future directions in this field are discussed and anticipated. Under the "carbon peaking" and "carbon neutrality" targets, it is essential to effectively utilize the thermal energy of molten steel slag, develop technologies for waste heat recovery and hot steel slag iron extraction, and use steel slag carbonation techniques to produce high value-added products, so as to realize comprehensive recovery and utilization of heat, iron and tail slag resources.

The steel industry is an important construction foundation and industrialization support for the development of the national economy,while also directly affecting the living standards and national security of the people. To actively respond to China's "carbon peak,carbon neutrality" and sustainable development policies,the future transformation direction of the Chinese steel industry will focus on high-quality development,green production,intelligent manufacturing,and enhancing international competitiveness,in order to achieve the goals of carbon reduction and sustainable development. Blast furnace ironmaking is an important part of steel production,with a complete automation system that generates a large amount of production data. In order to serve the intelligence of blast furnace ironmaking and promote the sustainable development of blast furnace ironmaking with these data. Data cleaning through data management technology can enhance data quality and provide a reliable basis for subsequent analysis. Based on the important parameters in the production process,the digital twin model of key variables is established by using big data analysis and artificial intelligence technology. Real-time monitoring,analysis and prediction can be carried out for multiple targets in the smelting process,combined with intelligent control strategies and optimization algorithms to achieve multi-objective collaborative optimization,which can improve production efficiency and reduce costs under the premise of ensuring production safety. The intelligence level and production efficiency of blast furnace ironmaking can be further improved by using data middle platform to integrate,analyze,apply and share the large amount of data generated by blast furnace ironmaking. Finally,the issues in the intelligentization of blast furnace ironmaking were summarized,and solutions were discussed in the conclusion. These insights provide guidance for the industry's transformation towards intelligence and contribute to the sustainable development of the steel industry.

Bottom blowing gas is an important method to enhance the stirring performance of steelmaking furnace, and the basic physical properties of the gas medium and its reaction characteristics with the molten bath directly affect the stirring power. In order to explore the influence of different kinds of gas medium on molten bath stirring, a new calculation model of molten bath stirring power in top-bottom combined blowing converter considering carbon-oxygen reaction was established by coupling the theoretical model of stirring power calculation, the law of decarburization and the law of molten bath heating in converter. The variation of molten bath stirring power with smelting time under the condition of bottom blowing reactive gas (O₂, CO₂) and inert gas (N₂) was revealed. The calculation results show that the stirring power of bottom blown N₂ varies positively with the molten bath temperature, and increases slightly with the increase of the temperature. The stirring power of bottom blown O₂ and CO₂ is closely related to the decarburization rate in the furnace. At the beginning and the end of converter smelting, stirring power of bottom blown O₂ is extremely low. Mixing CO₂ in bottom blown O₂ can improve the bath stirring, and reduce the equilibrium nitrogen content in end-point molten steel. The industrial test of 120 t converter shows that compared with bottom blowing O₂-N₂/Ar, bottom blowing O₂-CO₂ can obtain more excellent dephosphorization, oxygen control and denitrification effects, the heat proportion of achieving ultra-low phosphorus (mass fraction of phosphorus is not more than 0.005%) steel increases from 4% to 24%, the average carbon-oxygen product decreases from 0.001 9 to 0.001 7, and the average mass fraction of nitrogen decreased from 0.003 3% to 0.002 9%. The results can provide a theoretical basis for the process design of bottom blowing O₂-CO₂ in converters.

There is a common phenomenon of coke burning loss in the coke dry quenching (CDQ) process, which is the main source of sulfide and CO in CDQ system. By studying the variation law of coke burning loss rate in CDQ system, it can provide theoretical support for related pollutants control. Based on gaseous carbon balance in CDQ system, a real-time calculation method for coke burning loss rate was obtained. This method required obtaining volume fractions of CO and CO₂ in CDQ environment dust removal gas. Therefore, composition variation law of CDQ environment dust removal gas was studied, and there were CO₂ and CO and a very small amount of NO in the gas. The concentrations of those components change periodically, they increase rapidly and reach a peak during the coke loading operation, and then decrease rapidly and tend to flatten out. The actual variation law of coke burning loss rate was obtained by the above testing data. The coke burning loss rate varies periodically during normal production, while it decreases without coke loading for a time. There is a peak in coke burning loss rate caused by coke loading, and its contribution to coke burning loss rate in CDQ system is about 10%. Comparing the three real-time calculation methods of coke burning rate, it can be seen that the value obtained by imported air method is higher, while the value obtained by carbon (released gas) balance method is lower. Coke burning loss rate is too high when concentration of CO in circulating gas is too low, and it can be reduced to the design level by increasing concentration of CO in circulating gas and taking other measures.

The steel industry is an important foundational industry of the national economy. The traditional engineering design theory faces significant challenges in promoting high-quality development of the steel industry. Metallurgical process engineering theory is an important theoretical basis for guiding the high-quality development of steel industry in the new era. The application of metallurgical process engineering theory in the integrated steel plant engineering was introduced. It is to construct a static system and achieve dynamic-orderly,coordinated-continuous,and stable-efficient operation of material flow,energy flow,and information flow by thoroughly studying the manufacturing physical system,optimizing its parameters,adopting green "interface technology", and determining the steady-state optimization goals of the physical system. By applying the metallurgical process engineering theory,a "compact" steel manufacturing process was created for the Han-Steel Project. And the impact of ultimate design on production operation, efficiency, energy conservation, pollution reduction, and carbon reduction was determined. Han-Steel New Area covers an area of 0.42 m² per ton of steel,a comprehensive energy consumption of less than 546 kg standard coal per ton of steel,a new water consumption of 2.5 t per ton of steel,and CO₂ emissions of less than 1.57 t per ton of steel,becoming a model for energy conservation and carbon reduction in the steel industry. The ultimate design of integrated steel plant based on metallurgical processes theory has laid the foundation for the enterprise to achieve a world-class factory that is "efficient,green,and intelligent".

Charcoal consists of four parts, which are moisture,volatile matter,fixed carbon,and ash. Charcoal plays a key role as a covering agent in the preparation of oxygen-free copper. To optimize the treatment and usage conditions of charcoal,the role of charcoal in the melting and holding process of oxygen-free copper was explored. The micro-morphological and compositional variations of charcoal under different pretreatment conditions were investigated.The results showed that when the pretreatment temperature and time of 500 ℃-5 h,and 550 ℃-4 h,the water and volatile matter in the charcoal could be effectively released and the loss of fixed carbon was minimized.The ash in the charcoal reacted with the copper solution and phosphorus copper to form compounds such as Cu₂O and calcium copper phosphate (Ca₃Cu₃(PO₄)₄),resulting in copper and phosphorus loss.In the study on the thickness of charcoal cover, when the thickness of charcoal was 15-20 cm, the mass fraction of carbon in oxygen-free copper ingots was lower than 0.002%,the mass fraction of oxygen was lower than 0.000 5%, and the ingot defects were minimized with the highest material utilization.

Tangsteel New Area is a new generation of process steel plant designed and constructed by HBIS Group in accordance with high-quality development and green low-carbon transformation with the construction goal of "green, intelligent and branding", taking advantage of the opportunity of location adjustment. In the engineering design of Tangsteel New Area, the traditional static design of steel plant based on static capacity estimation of each process/device and different surplus coefficient assumption is abandoned, and the dynamic and accurate design of steel plant is used to construct the cyber-physical system of Tangsteel New Area under the guidance of metallurgical process engineering, laying a solid foundation for the optimization of the static structural framework of physical space and dynamic running path, trajectories and time-space boundaries. In order to implement the principle of dynamic and precise design, a series of digital technologies are used to build factory database platform, and integration planning schedule, system of whole processes dynamic scheduling, whole process digitalization, equipment intelligent operation and maintenance, and energy fine management system in the cyberspace. Through the mutual mapping, real-time interaction and efficient collaboration of the human, machine, material, method and environment in the cyberspace and the physical space, the resource allocation and operation in the cyber-physical system can respond on demand, quickly iterate and dynamically optimize, so as to solve the complexity and uncertainty problems in the process of production, manufacturing, and energy dissipation, then the material flow can be matched and equalized dynamically, stably and equably over a long period of time, the overall running time of the whole process and the energy consumption of the process can be minimized. Tangsteel New Area has contributed a green smart steel plant to the industrial upgrading of the metallurgical industry and the development of new quality productivity.

The iron and steel manufacturing process is a manufacturing system integrated through the coupling of multiple procedures. Its physical essence lies in the fact that the ferrous substance flow, driven and influenced by the energy flow, undergoes a series of complex physical and chemical conversions or transformations to produce steel products. The substance flow, energy flow and information flow are mutually coupled and operated in synergy in the process, and dynamic operation is the predominant characteristic of the process. The steel manufacturing process operates far from an equilibrium state, characterized by nonlinear coupling and being an open irreversible process that entails the dissipation of matter and energy. The steel metallurgy engineering design is a systematic integration and optimization endeavor based on research findings in fundamental science, technical science, and engineering science pertinent to steel plant design. Contemporary steel metallurgy engineering design is guided by principles of engineering philosophy as well as metallurgical process engineering theory. It involves the judicious selection and systemic integration of metallurgical processes and technical equipment to establish a rational workflow with advanced structures, optimized functions, efficient operations, and competitive engineering solutions. At its core, contemporary steel manufacturing engineering design aims to achieve integrated objectives encompassing systematization, structuring, functional enhancement, high efficiency, sustainability, greenization, and intelligence throughout the entire project while pursuing structural integrity, functional efficacy, operational efficiency, and multi-objective optimization within the metallurgical processes. The connotations and methods of concept design, top-level design and dynamic precise design of the new generation steel plants are discussed, and the innovation and practical effects of the engineering design of Shougang Jingtang Steel Plant are expounded.

Gear steel, as a key material in aerospace, railroad transportation and mechanical transmission, its performance directly affects the service life and reliability of gears. Aiming at the properties deterioration problem of gear steel due to banded organization during solidification at lower cooling rates, the microstructure and microsegregation behavior of solute elements of 20MnCr5 gear steel at different cooling rates were investigated by a combination of experimental and theoretical calculations using in-situ laser confocal scanning microscopy (CLSM), electron probe X-ray microanalysis (EPMA), and JMatPro software. The results show that the secondary dendrite arm spacing decreases from 318.63 μm to 138.08 μm with the acceleration of the cooling rate. During the solidification process of 20MnCr5 gear steel, the phase transformation of L→L+δ→γ mainly occurs. With the decrease of temperature, chromium and manganese elements have a tendency to be polarized at the grain boundaries, while MnS, TiN and carbides are precipitated successively. A microscopic segregation model of solute elements is constructed to predict the segregation behavior of elements in the solidification process of gear steel, and the results are consistent with the distribution of elements in the EPMA surface sweep, which provides a basis for the optimal control of the continuous casting process and the quality control of billet casting.

Shougang Jingtang Company follows the theory of metallurgical process engineering and has constructed a new generation recyclable steel manufacturing process with dynamic and orderly, continuous and compact, and efficient and stable production by analyzing and integrating the metallurgical functions of each unit production process in the production process. It adopts advanced "blast furnace-converter" and "continuous casting-hot rolling" interface technologies, as well as generic technologies such as hot metal pretreatment, matching between converter and continuous casting machine, optimizing and matching of steel refining, and high-efficiency continuous casting, to build a clean steel platform with high efficiency, low-cost, and stable production of high-quality steel. Through the continuous improvement of the scheduling model for the blast furnace-converter interface, the number of iron ladle turnover times has gradually increased from 3.8 times per day to more than 5.8 times per day, the temperature drop of hot metal has gradually decreased from 108.3 ℃ to 85.7 ℃, and hot metal charging accuracy (-0.5-0.5 t) has remained stable at over 98.5%. The continuous casting-hot rolling interface is based on the integrated platform of production and marketing, through the optimization of the rolling plan, the reduction of the blocking rate of the slab, and the online quenching technology of the slab, the hot charging rate of the hot rolling production line reaches 64.84%, and the hot charging rate of the medium-thick plate production line reaches 62.9%. In terms of specialized production, through reasonable optimization of process layout and differentiated equipment, specialized production lines with their own characteristics have been formed. The production line, represented by automotive sheet and tinplate, uses high efficiency production and low oxygen control technology throughout the entire process, to control the treatment time of KR, the treatment time of converter and the vacuum treatment time of RH within 32.2, 35, 20 min, respectively. The casting speed of peritectic steel is increased to 1.7 m/min, the casting speed of tinplate is up to 2.0 m/min, basically achieving the matching between converter and continuous casting machine. The oxygen mass fraction of molten steel in the tundish is reduced from 0.002 8% to 0.001 5%. The thin slab casting and direct rolling line represented by MCCR achieves efficient and stable production of ultra-low sulfur steel with w([S])≤0.001 2%, and low carbon and low silicon steel grades with w([Si])≤0.03%, w([S])≤0.001 5%, w([C])≤0.01%, and w(T[O])≤0.001% through ultra-clean steel technology. The surface quality of the pickled strip steel reaches the level of cold-rolled FB surface quality. For the medium-thickness plate production line represented by 9Ni steel, the slag system with ultra-high phosphorus distribution ratio and high-efficiency deep desulfurization, nitrogen, oxygen, hydrogen and inclusion control technology have been developed. The sum mass fraction of the five impurity elements (P+S+N+H+O) is as low as 0.004 01%. By using the slab heavy reduction technology, the center porosity of 300 mm and 400 mm thick slabs is not greater than 0.5 grade. Shougang Jingtang Company fully leverages the advantages of the new generation process, led by strategic products such as automotive sheet and tinplate, and has achieved first-time launches of a number of product technologies, realizing the brand concept of "making the best steel".

In the process of steelmaking and continuous casting,there will be many disturbances,resulting in the scheduling can not be carried out according to the original plan in many times,so it is necessary to adopt real-time scheduling strategy for dynamic scheduling of steelmaking and continuous casting production process. In order to ensure the stability of steelmaking and continuous casting process,a dynamic adjustment method based on "adjustable" buffer time and Flexsim backward working method was proposed. The rescheduling job plan was generated by adding restrictions such as crane rules,equipment selection rules,and ladle quantity limits. Through the optimized dynamic scheduling scheme,the influence of the disturbance in the process of steelmaking and continuous casting was well eliminated. In addition,comparing the present research scheme with the manual scheduling in terms of evaluation indexes such as equipment utilization,degree of continuity and production cycle time,the average production cycle time was reduced by 7.9 min and the degree of continuity was increased by 8.8%. The results show that this method can not only dynamically generate specific scheduling schemes based on rules and Flexsim,but also significantly improve the related indexes of the process,which provides a theoretical basis for Flexsim to guide field production in the future.

The cohesive zone of blast furnace is one of the key factors to ensure the reasonable distribution of gas flow and low-carbon smelting. Its position and shape are mainly affected by the metallurgical properties of iron-containing burden and the interaction of high temperature. The mechanism and influencing factors of high temperature interaction between different iron-containing burdens such as sinter, pellet and lump ore, and the influence of high temperature interaction on the softening and melting properties of burdens and the formation of slag phase are reviewed. It is pointed out that the interaction between iron-bearing burdens can be optimized by properly adjusting the chemical composition and mixing degree of burdens, optimizing the structure of burdens and improving the reduction conditions of burdens, so as to improve the softening and dripping properties and gas permeability of burdens. In the future, the research on the interaction mechanism of high-quality pellets such as cold-pressed pellets, metallized pellets and fluxed pellets with other iron-containing burdens can be strengthened, and the correlation between the phase evolution and the diffusion kinetic behavior of different iron-containing burdens during the interaction process of burdens can be deepened, so as to provide reference for the optimization of softening performance and permeability of burdens.

There are complex non-linear relationships between various process parameters and control targets in continuous casting process. Traditional methods, such as numerical simulation and laboratory experiment, cannot meet the requirement of efficient production of enterprises due to their poor optimization efficiency. At present, machine learning has been widely used in the abnormal prediction, quality detection and process optimization with the aims to improve productivity and slab quality, as well as accelerate the development of new technologies and digital transformation in continuous casting. Current advancements of machine learning application in the predicted strategy, feature extraction and model construction in various stages of continuous casting process are summarized. The results show that the machine learning offers higher predictive accuracy and better generalization ability in continuous casting production compared with the traditional methods. It also can achieve fine and intelligent control of continuous casting process after building corresponding models for different prediction targets. Meanwhile, feature research directions for machine learning application in continuous casting production are also proposed from three aspects of sample distribution, data quality, and model development/application. This outlook aims to provide valuable references for the intelligent advancement of continuous casting.

Cr12MoV steel is the most widely used cold work die steel, which belongs to high chromium and high carbon lesteritic steel, and the form, quantity, size and distribution of carbides in the steel have an important impact on the properties of Cr12MoV steel. Metallographic microscope, scanning electron microscope, three-dimensional corrosion engraving device for inclusions, X-ray diffractometer and energy dispersive analyzer were used to analyze the type, morphology and distribution of carbides in Cr12MoV die casting billets in a factory, and the phase transition and carbide precipitation behavior of Cr12MoV cold work die steel were calculated by Thermo-Calc 2020b. The results show that the carbide types of Cr12MoV cold work die steel are chromium-rich and iron-rich M₇C₃ carbides and M₂₃C₆ carbides, the main elements of M₇C₃ carbides are chromium, iron, carbon and molybdenum, and the main elements of M₂₃C₆ carbides are iron, chromium, molybdenum and carbon. The carbide morphology in the casting billet can be mainly divided into four categories, granular carbide, bulky carbide, rod-like carbide, and reticulated carbide. The size of granular carbide is 2-5 μm, the size of bulk carbide is 10-15 μm, the size of rod carbide is 30-40 μm, and the reticulated carbide is formed by the aggregation of granular, bulky and rod-like carbides and its size is up to 80 μm. The evolution of carbide morphology from edge to core is as follows, granular→ blocky→ rod-like → reticulated, the heterogeneity of carbide from edge to core is gradually enhanced, and the carbide at the edge is distributed in a granular manner, the carbides at 1/4 are long rod-shaped, and the carbides in core are segregated into a network. From edge to core, the average equivalent diameter of carbide increases from 5.7 μm at the edge to 8.5 μm at the core, the proportion of carbide area increases from 8.2% to 9.5% from the core, and the density of carbide decreases from 2 961/mm² at the edge to 1 189/mm² at the core. By analyzing the type, morphology and distribution of carbides in Cr12MoV steel billets, the distribution law of carbides in the casting billets is found, which provides a theoretical basis for the factory to regulate the carbide morphology in the steel and optimize the performance of steel.

The changes of China's annual crude steel output, average daily crude steel production on a monthly basis over the past two years, end-of-month rebar prices, direct steel exports, indirect exports of steel products, and CO₂ emissions were reviewed and analyzed. It is concluded that China's crude steel production is generally in a situation of oversupply, and the steel industry has entered a downward phase of reduction fluctuations. Under the premise of no significant increase in crude steel output, China's steel industry can be considered to have entered a CO₂ emission stabilization period. The study explores targets and measures for total crude steel output control from perspectives including future production forecasts, supply-side structural reforms, and adjustments to import/export policies. By integrating projections of future crude steel output and scrap resources, it is proposed that under the goals of "Carbon peak and Carbon neutrality", China's steel industry will gradually develop three typical manufacturing processes:BF-BOF long process, full scrap EAF process, and hydrogen reduction-EAF process. The evolutionary alternation of these three processes is discussed, emphasizing that China's steel industry should leverage the "Carbon peak and Carbon neutrality" context to guide scrap resources toward EAF process, thereby gradually optimizing the sector's ferrous resource structure, product structure, and process structure. Pathways for enhancing manufacturing continuity are explored through interface technology optimization, dynamic precision design, and full-process intelligentization. Finally, through the construction and analysis of a "dual carbon" analytical model for the steel industry, the study identifies controlling and reducing crude steel output as the most effective decarbonization measure, with process structure optimization in steel plants being equally critical.

Lightweight is an important path for the automotive industry to address the air pollution problems and deliver on the goals of carbon peaking and carbon neutrality. The medium-manganese low-density steel,with Mn mass fraction of 3% to 12%,has low costs and good processing performance,showing excellent potentials for development and application in the field of automotive steel. The strengthening mechanism of medium-manganese Fe-Mn-Al-C low-density steel was systematically introduced based on the current research status at home and abroad,while the influence and mechanism of heat treatment process on the mechanical performance and strengthening mechanism of medium-manganese low-density steel were comprehensively summarized. In addition,the stability of residual austenite during deformation process was discussed. The characteristics of quenching and partitioning (Q&P) were analyzed according to the development process and current situation. The strengthening mechanism for quenched and proportioned steel was explored along with the influencing factors of mechanical properties of medium-manganese steel from such perspectives as heating temperature,quenching temperature,partitioning temperature and partitioning time. Based on the urgent need of boosting the comprehensive performance of medium-manganese Fe-Mn-Al-C lightweight steel,and on account of its element composition and microstructure characteristics, the volume fraction and stability of residual austenite in medium manganese Fe-Mn-Al-C low-density steel can be increased by Q&P process, as well as the mechanical performance will be enhanced,is proposed. The future research directions deserving attention need to be paid attention, firstly,reasonable Q&P process need to be controlled to avoid the precipitation of coarse κ-carbides in steel; secondly, the synergistic effect between κ-carbide strengthening and TRIP effect in medium-manganese need to be explored; finally,the effect of Q&P process on the size of original austenite grains and the non-uniformity of the martensitic structure during the phase transformation process needed to be analyzed, as well as the effect of different substructure characteristics of martensite on the nucleation sites and morphological features of residual austenite, so as to provide reference for the popularization,optimization and improvement of the production process.

In order to match the blast furnace and sintering capacity of Anshan Steel, increase the sintering production and solve the problem that the thickness of sinter layer cannot exceed 900 mm with high-proportion concentrate, Anshan iron and steel group developed a double-layer pre-sintering process, however, the sintering yield decreased and the sintering with grade of [5, 10) mm increased in the industrial production process. Therefore, the basic research on the 1 000 mm double-layer pre-sintering process with stand-support was carried out in the laboratory. The results show that during the double-layer sintering, after the second ignition, the content of CO₂ and CO are increased, the volume content of O₂ is dropped sharply to about 8%, and the bottom mixture layer burns in a low-oxygen atmosphere for a certain period of time. The change of air permeability index during double-layer sintering can be divided into three processes. After adding the stand-support, the average index increases 10.37% and 12.61% of the first stage and the second stage, respectively, and the average index of the lowest point in the third stage increases 28.95%. After adding the stand-support, the time that at the lowest content of oxygen is advanced, and the content of oxygen is increased. Also, the sinter drum strength is decreased, but the yield of sinter is increased. The utilization coefficient can reach 2.12 t/(m²·h), and the quasi-fine ratio of [5, 10) mm is reduced significantly. The stand-support of 350 mm can be obtained better technical index compared with the stand-support of 400 mm. Results in laboratory prove that, the stand-support sintering of double-layer process can solve the key problems in actual application and can release its production capacity further.

With the rapid development of the automobile industry, the surface quality of the automobile sheet is becoming more and more severe in the main machine factories at home and abroad, especially the "sand hole" phenomenon of the substrate surface in the stamping process of the ultra-deep drawing and large reduction complex forming automobile sheet, becomes the restriction factor which limits the automobile board high quality development. In view of the "sand hole" defect in the stamping of automobile sheet with ultra-deep drawing and large reduction, by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it was clear that the removal of Al₂O₃ inclusions enriched by submerged nozzle was the fundamental cause of "sand hole" defect in sheet metal stamping. Through the analysis of the correspondence between the key steelmaking process and the "sand hole" defect, it was shown that the main causes of the "sand hole" defect were the end-point oxygen of the converter, the top slag TFe of the RH outlet, the fluctuation of the mold level, and the continuous casting of transition blank were the main causes of "sand hole" on the substrate surface. The cleanliness of molten steel can be improved by reducing oxygen content in molten steel, optimizing TFe content in RH slag, reducing oxygen transfer at slag/gold interface, protecting casting to prevent secondary oxidation of molten steel, optimizing flow field of mold to reduce fluctuation of liquid level and steady state control of liquid level in tundish. The "sand hole" defect of the ultra-deep drawing and large thinning volume automobile sheet is effectively improved, and the defect incidence is reduced from 0.086% to 0.026%. The research results provide technical support for high cleanliness smelting of ultra-low carbon steel, and provide reference for improving the surface quality of ultra-deep drawing and large reduction automobile sheet.

Reducing the content of alkali metal in pellet is beneficial to reduce the alkali load of blast furnace. Therefore, the application of two kinds of low alkali metal bentonite in pellet production was studied. The results show that under the same ratio, the drop strength (0.5 m) of green pellet using these two kinds of low alkali metal bentonite increases from 5.0 times to 5.2 times and 8.8 times, respectively. The mass fraction of alkali metal decreases from 0.203% to 0.142% and 0.146%, respectively. The reduction swelling index decreases from 13.8% to 11.9% and 12.7%, respectively. The low temperature reduction degradation indexes IRD,>6.3 mm, IRD,>3.15 mm and IRD,>0.5 mm have a good trend. One of the low alkali metal bentonites was used in the pellet production of a steel plant. The results show that the alkali metal mass fraction of pellet with low alkali metal bentonite decreases by 0.055 percent point while the compressive strength changes little, and the reduction swelling index has a decreasing trend. The application of low alkali metal bentonite in pellet production is beneficial to reduce the content of alkali metal in pellet, which has a positive effect on the normal smelting of blast furnace and the long life of blast furnace.

Hydrogen-rich smelting and increasing the proportion of pellets into blast furnace are important ways to promote the low-carbon blast furnace ironmaking. Taking iron ore oxidized pellets as the object, the effects of reducing atmosphere and temperature on the thermal compressive strength of pellet were experimentally investigated, and the evolution law of the thermal compressive strength of pellet under different conditions was clarified. The results show that the thermal compressive strength of pellet decreases with the increase of reducing gas (CO or H₂) concentration during the isothermal reduction process, and the decrease of thermal compressive strength of pellet at 900 ℃ is significantly higher than that at 700 ℃. When the volume fraction of H₂ increases from 0 to 40%, the thermal compressive strength of pellet slowly decreases from 865 N to 757 N at 700 ℃, and significantly decreases from 632 N to 29 N at 900 ℃. During the non-isothermal reduction process, when the reduction temperature increases from 500 ℃ to 900 ℃, the thermal compressive strength of pellet under the inert atmosphere gradually decreases from 1 551 N to 1 016 N, and that under the non-hydrogen-rich atmosphere decreases from 1 495 N to 244 N, and that under hydrogen-rich atmosphere decreases from 1 275 N to 289 N. As the temperature is less than 800 ℃, the thermal compressive strength of pellet under hydrogen-rich atmosphere is higher than that under non-hydrogen-rich atmosphere, and when the temperature is greater than 800 ℃, the thermal compressive strength of pellet under hydrogen-rich atmosphere is slightly lower than that under non-hydrogen-rich atmosphere. This study could provide theoretical basis and data support for hydrogen-rich smelting and large proportion pellet smelting.

The hydrogen metallurgical electric furnace process is an important starting point for the steel industry to achieve green and sustainable development due to its potential to achieve nearly zero carbon emission steel production. The direct reduction iron provided by hydrogen metallurgy needs an electric furnace to obtain the ideal steel material because it is not a terminal product. The electric furnace process technology has been mature,but the technological breakthrough of the hydrogen metallurgy process is still a big challenge. The hydrogen metallurgy process is widely regarded as a frontier disruptive technology. Most of the domestic hydrogen metallurgy demonstration projects are in the industrial test stage,and there is still not enough to achieve the realization of real industrialization. The evaluation of the technology readiness of the hydrogen metallurgy process is helpful to scientifically understand its development history,evaluate its development status,and expect its future development trend. Based on the technical readiness criteria and process analysis,the technical readiness evaluation criteria and detailed rules suitable for hydrogen metallurgy processes were studied to evaluate and prospect the four kinds of hydrogen metallurgy processes. The results show that the comprehensive evaluation of the direct reduction process of a hydrogen-based shaft furnace is level 7,the direct reduction process of a hydrogen-based fluidized bed is level 6,the process of hydrogen-rich blast furnace ironmaking is level 7,and the hydrogen-based melting reduction ironmaking process is level 6. On the whole,the hydrogen metallurgical process is still in the stage of continuous exploration and development,and there are no mature and commercial manufacturers. Finally,the historical development process of the main hydrogen metallurgy process route is reviewed,and the future development trend and prospect of hydrogen metallurgy are discussed. Among the four processes,the direct reduction process of hydrogen-based shaft furnaces is expected to be commercialized at the earliest,and the replacement of hydrogen for carbon in the metallurgical process,helping to achieve nearly zero carbon emissions in steel production.

Large clusters in steel are formed by collision and aggregation of fine and uniformly distributed solid inclusions, which have irregular fractal characteristics. Therefore, the fractal dimension can be used to quantitatively describe the morphology of inclusions. In order to describe the morphology of non-metallic inclusions in steel quantitatively, the research on the fractal dimension of clustered inclusions is organized. Firstly, the definition and different calculation methods of the fractal dimension, the measurement method of three-dimensional fractal dimension(D₃), and the models for the transformation between the three-dimensional and two-dimensional fractal dimensions are summarized. Secondly, the main factors affecting the fractal dimension of inclusions are analyzed, including the composition of inclusions and the calculation error. The fractal dimension of large clusters is about 1.7-1.8. In the process of boxcounting dimension calculation, the calculation error comes from the selection of the maximum size of the covering box. When 0.25≤ε/dmax≤1, the calculation error of inclusion fractal dimension is avoided. Finally, the application of fractal dimension in the study of inclusions is summarized. The theoretical floating velocity of irregular clusters in molten steel can be calculated by fractal dimension. The floating velocity of inclusions increases with the increase of fractal dimension. The fractal dimension can be used to study the morphology of aggregates formed by inclusions after collision and aggregation. Based on the development of fractal theory, the diffusion-limited aggregation model (DLA model) is proposed to simulate the aggregation of inclusions in steel. As the distance between the release point of particles and seeds decreases, the particle size increases, and the seed size increases, the aggregation degree of inclusion increases. The stopper or nozzle can be considered as large seeds, and inclusions are easy to gather on its surface, which cause the nozzle clogging. The stopper or nozzle clogging can be reduced by improving the wettability between the stopper and inclusions. The aggregated clusters inclusions are in a chain or more dispersed branched structure with the increase of aggregation ratio between the basic particles. The result provides guidance for researching into the collision and aggregation process of clustered inclusions, which facilitates removal fraction by floating to the surface of the molten steel, enhancing the cleanliness of the steel.

In order to improve the high-temperature strength of heat-resistant steel, adding trace alloying elements to the steel is an effective measure when designing alloy. Nb microalloying is the main strengthening method of heat-resistant steel and has always been a hot research topic in heat-resistant steel. Based on the application of Nb, the alloying development process and current situation of martensitic heat-resistant steel for steam generator rotor, martensitic heat-resistant steel and austenitic heat-resistant steel for ultra-supercritical boiler are described. Most of the rotor martensitic heat-resistant steels contain a small amount of Nb, especially the martensitic rotor steels developed in the last 40 years contain about 0.05%Nb (mass fraction). The general Nb mass fraction of martensitic heat-resistant steel for small and medium-size parts of steam turbines is about 0.05%-0.25%. The Nb mass fraction of martensitic heat-resistant steel used for steam turbine shell is about 0.05%-0.10%. And T/P91 and T/P92 steels for main steam pipes and heat exchange tubes are containing 0.04%-0.25%Nb. Nb and V is used together in martensitic heat-resistant steel, and the V content is about 2 to 4 times that of Nb. The content of Nb in typical austenitic heat-resistant steel is about an order of magnitude higher than that in martensitic heat-resistant steel, and Nb is generally added separately in austenitic heat-resistant steel, or a small amount of Ti is added in combination. On the whole, with the increase of steam parameters for power plant boiler, the alloying degree of martensitic heat-resistant steel and austenitic heat-resistant steel becomes higher and higher, and the types of alloying elements in steel become more and more. For austenitic heat-resistant steels, controlling and improving the existing form of primary Nb-rich phase is the main focus in the future. With the increase of strengthening factors in steel, the qualitative/quantitative interaction between strengthening factors may become a key research direction.

Online isothermal heat treatment (QM) of special steel wire refers to a new type of online isothermal heat treatment technology that uses the residual heat from rolling to directly immerse the wire into a constant temperature salt bath to control cooling after wire drawing. QM technology has the characteristics of fast cooling rate and wide temperature range, and can be used for special steel wire products such as ultra-high strength high-carbon pearlite steel, medium-carbon bainite non-quenched and tempered steel, and non-annealed low-carbon alloy steel. Ultra-high strength high-carbon pearlite steel wire rod is used to manufacture galvanized aluminum steel wire for bridge cable, which can achieve tensile strength of 2 130 MPa and torsion times of more than 18 times. Medium-carbon bainite non-quenched and tempered steel obtains the full bainite structure through the controlled cooling process without adding precious alloying elements, which meets the strength requirements of standard parts in strength classes 8.8, and can achieve 1/6 cold top forging without cracking. After QM treatment, the section area reduction rate of non-annealed low-carbon alloy steel is significantly higher than that of the traditional slow cooling process, and the deformation capacity is higher, which can realize annealing-free drawing processing. QM technology eliminates the secondary heat treatment and realizes the reduction of alloying elements, which has broad market prospects under the background of "carbon peaking" and "carbon neutrality". The QM process flow, technical principles, and the latest research and development progress of related products are introduced.

In order to reduce the energy consumption and carbon emission of sintering process, a new technology of fuel separated addition in sintered material surface coupled with low temperature ignition was proposed, which could significantly reduce the ignition temperature under the premise of ensuring ignition effect, by adding 5%-7% of the total fuel on the surface of sintered layer and using the rakes and levelling boards to make the fuel uniformly distributed. Thereby, the consumption of solid fuel and ignition gas were reduced. The technology has been applied in Xiangtan Iron and Steel Co., Ltd., and the practical results show that, after adopting the technology, the ignition temperature of three sintering machines has decreased by 16%-27%, the flow rate of gas fuel has decreased by 640-1 900 km³/h, and the ignition energy consumption of sintered ore has decreased by 0.007-0.038 GJ/t. Meanwhile, the intensity of rotating drum is maintained at the original level, and the solid fuel consumption of sintered ore is reduced, the SO₂ and NO_x content in the flue gas decreases significantly. The application of the new technology achieves energy saving and carbon reduction result.

With the progress of energy-saving work, the difficulty of energy-saving of steel industry in China is increasing, and the potential is decreasing under traditional technological systems in steel manufacturing processes. In the new period of high-quality development on the constraint of the "dual control" of energy consumption and carbon emissions, the steel industry is entering a new stage with efficient energy conversion, intelligent energy-flow dispatching, and integrated matching optimization. Networked operation and intelligent dispatching of energy flow are important means to explore greater potential for energy-saving. Modeling for energy flow network is the foundation for intelligent dispatching and integrated optimization of energy system. Petri Net, as a formal model for describing net systems, is a modeling tool for describing the relationships between units and the resource changes in directed net systems. Both Places and Transitions have into two types: continuous and discrete, to represent continuous variables and discrete events respectively, and thus form a hybrid Petri Net for modeling hybrid system. Based on metallurgical process engineering, the essential features of the steel manufacturing process and its energy flow network system were analyzed, and the system structure and dynamic characteristics of the energy flow network for steel manufacturing process were analyzed as a "directed network" from "system" perspective. Based on the hybrid Petri Net modeling method, an energy flow network model for steel manufacturing process was developed by formally abstracting. This model can qualitatively and quantitatively describe the relationships between elements of the energy flow network system, thus visually and realistically describing the system structure and dynamic characteristics. Taking a typical steel plant as an example, the Petri Net model for the energy conversion process was established and simulated by Matlab software with a 1 h step based on production performance data from a sample day. The simulation results show that the model matches well with the actual system. This method can provide technical support for the energy evaluation, dynamic dispatching and optimization of the energy flow network system for steel manufacturing process.