Against the backdrop of an accelerating transformation toward high-end, intelligent, and green development in the iron and steel industry, hot metal pretreatment, as a key process for improving steel quality, is increasingly highlighting its importance. The development history of desulfurization processes in hot metal pretreatment both domestically and internationally are outlined, with a focus on analyzing the principles, current application status, and advantages and disadvantages of the two mainstream technologies, composite injection desulfurization and mechanical stirring desulfurization. It also reviews the development trends of current high-efficiency desulfurization technologies. Thermodynamic and kinetic analyses indicate that both injection desulfurization and mechanical stirring desulfurization have distinct advantages and disadvantages, yet they exhibit strong complementarity. Integrated technologies that combine the strengths of both injection and mechanical stirring methods have emerged as a trend in the development of new high-efficiency desulfurization technologies. Through multiple iterations of technological research, Pangang Group Xichang Steel and Vanadium has successfully developed a new high-efficiency rotating injection desulfurization technology. This innovation fully integrates the advantages of composite injection technology, such as strong desulfurization capability, deep immersion of desulfurizing agents into hot metal, fine particle size, and low usage of desulfurizing agents, with the strengths of the KR technology, including powerful mechanical stirring and excellent flow field control. By achieving thorough refinement and dispersion of injected powder bubbles through mechanical stirring, this technology demonstrates significant advantages in the desulfurization treatment of high-sulfur hot metal, including high desulfurization efficiency, low temperature drop, low iron loss, and low cost. It is expected to become a new-generation technology for high-sulfur hot metal pretreatment desulfurization.

With the growing demand for low-carbon blast furnace smelting and cost reduction in the steel industry, the use of domestic iron concentrate to prepare basicity pellets has become a trend in blast furnace ironmaking. Addressing the current issues with basicity pellets, such as insufficient mechanical strength, uneven calcination reactions, and reduced smelting efficiency due to an unreasonable particle size distribution of Shirengou iron concentrate, the effects of iron concentrate particle size ratio on the green pellet strength, bursting temperature as well as compressive strength, metallurgical properties, and microstructure of finished pellets were systematically investigated. The results indicate that as the ratio of coarse particles increases, the drop strength and compressive strength of green pellets gradually decrease, while the bursting temperature gradually increases. The compressive strength of finished pellets first increases and then decreases. As the ratio of medium particles increases, the trends in strength and bursting temperature of green pellet are consistent with those of coarse particles. Still, the compressive strength of finished pellets gradually decreases. The green pellet strength increases slowly with the ratio increase of fine-grain particles, while the bursting temperature decreases. The compressive strength of finished pellets initially increases and then slightly decreasing. An appropriate amount of medium and coarse-grain particles plays a "core" and "scaffold" role in pelletizing, ensuring the rationality of pores within the pellets. An increase in the ratio of fine-grained particles is beneficial for improving pellet performance. In green pellets, it increases the specific surface area to enhance molecular bonding strength, resulting in closer particle contact, which promotes the formation of hematite crystal bonds and calcium iron oxide in finished pellets, thereby improving overall metallurgical performance of finished balls. However, excessive amounts of fine-grained particles reduce the hydrophilicity and ballability of iron concentrate, hinder the oxidation process, exacerbate lattice expansion, and deteriorate pellet quality, resulting in a more fragile mineral phase structure. When the iron concentrate particle size distribution ratio（mass fraction） of >0.074, [0.044,0.074], and <0.044 mm is 10%, 20%, and 70%, respectively, the pellet quality is optimal.

In order to investigate the effect of free basicity on the composition in binding phase of Bayan Obo pellets and reveal its mechanism of action on compressive strength and composition structure of pellets, taken Bayan Obo iron concentrate as research object, the process system of belt roasting machine was simulated. By means of the FactSage 8.2 thermodynamic simulation software, metallographic microscope, SEM-EDS（scanning electron microscopy-energy dispersive X-ray spectroscopy）and EPMA（electron probe micro-analysis）, the phase evolution, microstructure change,and element transfer mechanism of pellets under different free basicity conditions were systematically analyzed. The results show that as the free basicity （R_o） increases from 0.3 to 1.3, the liquid phase formation temperature of pellets first increases and then tends to stabilize, while the theoretical liquid phase yield gradually increases. When R_o increases to 0.9, the compressive strength of pellets reaches its maximum value. At this point, the mass fraction of liquid phase is 10.60%, the mass fraction of calcium ferrite is 8.00%, and the total mass fraction of binding phase is 18.60%. When R_o continues to increase beyond 1.1, the amount of binding phase decreases.EPMA tests show that the micro-area components of liquid phase in pellets with different R_o are mainly CaO and SiO₂. As R_o increases from 0.7 to 1.3, the liquid phase basicity increases from 0.92 to 1.53. The calcium ferrite phase is dominated by Fe₂O₃, with its mass fraction ranging from 78% to 84%. During the formation of binding phase, Ca elements preferentially react to form silicate liquid phase, and then form calcium ferrite phase. When R_o is less than 0.9, Ca elements mainly form the silicate liquid phase. When R_o is 1.1, approximately 66% of the Ca element mass fraction enters the silicate liquid phase, and 34% enters the calcium ferrite phase. When R_o is further increased to 1.3, the mass fraction of Ca elements forming calcium ferrite increases to 40%.The research results not only reveal the influence mechanism of R_o on the formation process of pellet binding phase, but also clarify the composition of calcium ferrite and the liquid phase as well as the reaction mechanism of Ca elements. This provides theoretical support for optimizing the preparation process of basic pellets.

To reduce the SiO₂ mass fraction and production cost in fluxed pellets,low-silicon titanium-containing PMC powder is used to replace high-silicon Chilean concentrate for producing low-titanium fluxed pellets,which is of great significance for establishing a raw material system suitable for high-proportion pellet-based hydrogen-enriched ironmaking. The preparation technology and metallurgical properties of low-titanium fluxed pellets with different TiO₂ contents were systematically investigated in a blast furnace with a hydrogen-rich system. By integrating FactSage thermodynamic calculations,XRD（X-ray diffractometer）,and SEM-EDS（scanning electron microscopy-energy dispersive spectroscopy） analyses,the mechanism underlying the influence of TiO₂ content on liquid phase formation,mineral composition,and microstructure of the pellets was elucidated. The findings reveal that increase in TiO₂ content inhibits liquid phase formation. However,when the temperature exceeds 1 240 ℃,the sharp increase in liquid phase disrupts the crystalline bond connections of hematite. Given the narrow range of suitable firing temperatures,the pellet firing temperature should be controlled at around 1 240 ℃. As TiO₂ mass fraction increases from 0.43% to 0.93%,the compressive strength exhibits a trend of first increasing and then decreasing,peaking at 3 142 N when TiO₂ mass fraction is 0.68%. This phenomenon is primarily attributed to the fact that,at low TiO₂ contents,the microcrystalline structure and recrystallization bonding of ilmenite promote densification of the pellet structure. With further increases in TiO₂ content,Ti dissolves into titanium hematite in the form of solid solution,reducing the Fe content in titanium hematite and becoming detrimental to hematite crystallization. Both the degree of reduction and reduction swelling rate show a decreasing trend,primarily due to the increased content of refractory ilmenite and pseudobrookite. The low-temperature reduction pulverization index（I_{RD>3.15 mm}）also follows trend of first increasing and then decreasing,reaching a maximum of 97.3% at TiO₂ mass fraction of 0.68%. An appropriate increase in TiO₂ content can refine grain size and thus enhance anti-pulverization performance. However,excessive TiO₂ content exacerbates pulverization due to internal stresses arising from the differential reduction of intimately associated titanium hematite and pseudobrookite.

The carbon emissions from ironmaking process account for more than 70% of the steel industry. Driven by the "carbon peak" and "carbon neutrality", the hydrogen-enriched blast furnace（BF） has become a dominant research interest. Hydrogen or hydrogen-enriched gas is injected through the tuyere to replace partial carbon with hydrogen, so as to reduce carbon emissions. The one-dimensional kinetic model of hydrogen-enriched blast furnace was established based on the rate equations and control equations of blast furnace operation, and the effect of hydrogen injection on smelting behavior was simulated, while the industrial data of blast furnace were used to validate, and the influences of hydrogen injection rate on indirect reduction degree and the thermal reserve zone （TRZ） were investigated. It shows that with the increase of hydrogen injection rate, the average temperature in the TRZ increases from 1 052 K （without hydrogen injection） to 1 243 K （with hydrogen injection of 100 m³/t）. Meanwhile, the upper and lower boundaries of TRZ moves down by 0.1 m and 1.5 m, respectively. Totally, the height of TRZ increases 1.4 m. The overall indirect reduction degree in the blast furnace is improved from 60.68% to 70.65%. The calculation results from the one-dimensional kinetic model and the energy-material balance model are in good agreement with each other, increasing the amount of hydrogen injection is conducive to the indirect reduction. On the whole, the reduction rate accelerates, further reducing the carbon consumption of direct reduction in the high temperature region. The result has vital theoretical value for digitization of the low-carbon blast furnace, further promoting the low-carbon transformation of steel industry. With the breakthrough of hydrogen preparation technology and the optimization of injection parameters with digital model, hydrogen-enriched BF process is expected to become the core path in the period of transition to "hydrogen metallurgy".

With the rapid development of the automotive industry and the advancement of the "Dual carbon" goals, the high carbon emissions associated with producing automotive sheet steel through the traditional blast furnace-basic oxygen furnace （BF-BOF） route have become increasingly prominent. The full-scrap electric arc furnace （EAF） process, capable of significantly reducing carbon emissions, has emerged as a key pathway for the low-carbon transition in the steel industry. The production landscape of automotive sheet steel was analyzed and the opportunities for its manufacturing was discussed via the full-scrap EAF process. Based on automotive sheet classification, typical steel grades within each category and their current EAF production status were examined. Classified by grade, typical steel types and their current EAF production status were examined. The main challenges were highlighted, including scrap treatment and the control of gaseous elements （such as nitrogen, hydrogen, oxygen）, carbon, harmful elements, and other residuals, and comparing the differences between EAF-produced and BF-BOF-produced automotive sheets. By analyzing actual production cases, successful practices in areas such as scrap processing, smelting process optimization, and industrial chain synergy were summarized. Research indicates that producing automotive sheet steel via the full-scrap EAF process is technically feasible. Industrial-scale mass production has been achieved for mild steels, specifically low-carbon steels. Mainstream grades for traditional high-strength steel of carbon-manganese （C-Mn） steel, bake hardening （BH） steel, and high-strength low-alloy （HSLA） steel, first-generation advanced high-strength steels （AHSS） of dual-phase （DP） steel, transformation-induced plasticity （TRIP） steel, martensitic （MS） steel, and complex-phase （CP） steel and third-generation AHSS of quenching and partitioning （QP） steel have entered industrial production. However, technical challenges remain for interstitial-free （IF） steel （within mild steels）, second-generation AHSS, and carbon-free bainitic （CFB） steel （within third-generation AHSS）. In the future, through technological upgrades, intelligentization, and industrial chain collaboration, the short-process route is expected to become the mainstream direction for green manufacturing of automotive steels.

With the continuous development of efficient railway transportation, the quality requirements for rails are constantly increasing, and the control of non-metallic inclusions in heavy rail steel is becoming increasingly stringent. Large non-metallic inclusions can deteriorate the service performance of rail and even reduce the pass rate of online flaw detection, adversely affecting both the production cost control of rails and the service performance of tracks. In particular, when the inclusions contain hard MgO-Al₂O₃ spinel particles, the inclusions can significantly exacerbate their detrimental effects on rail performance. Based on this, the evolution of non-metallic inclusions throughout the smelting process of U75V heavy rail steel produced by a certain rail manufacturer was investigated. The evolution of non-metallic inclusions from Al₂O₃-SiO₂-MnO system to Al₂O₃-SiO₂-CaO-MgO system from converter end point to continuous casting was clarified, the change patterns and reasons for the w（T[O]）, w（[N]）, number density, size distribution, and average composition of non-metallic oxide inclusions in steel were explained. The thermodynamic conditions for the formation of MgO-Al₂O₃ spinel in Al₂O₃-SiO₂-CaO-MgO system inclusions were clarified using FactSage 8.2 thermodynamic software. The results show that when the mass fraction of Al₂O₃ is less than 30% and the mass fraction of MgO is less than 2% in the inclusions, MgO-Al₂O₃ spinel can not precipitate from the inclusions. Controlling the contents of MgO and Al₂O₃ in inclusions is of great significance to control the formation of large-sized inclusions in heavy rail steel. It is confirmed that large-sized inclusions containing MgO-Al₂O₃ spinel are foreign inclusions based on the discussion on the influence of molten steel composition on inclusions. Combined with the detection and analysis of erosion behavior of immersed nozzle, the formation mechanism of large-sized Al₂O₃- SiO₂-CaO-MgO inclusions containing MgO-Al₂O₃ spinel is revealed, and put forward control strategies involving optimization of tundish refractories, covering agent composition, and submerged nozzle types, which provides valuable guidance for controlling large non-metallic oxide inclusions in heavy rail steel.

Constructing the mapping relationship between material preparation process, microstructure, and mechanical properties has always been an important direction in the research of metal material design and optimization. Traditional data-driven models for predicting the mechanical properties of metal materials only establish the relationship between the preparation process, material composition, and final mechanical properties, while overlooking the significant impact of microstructure on mechanical properties during material preparation. To improve the prediction accuracy of the mechanical properties model for 316 stainless steel thin strips, using a residual network algorithm combined with rolling process data and microstructure image data to build a mechanical properties prediction model for 316 stainless steel thin strips. Prior to modeling, rolling process data for thin strips of different specifications was collected via a rolling mill data acquisition system to generate high-quality process datasets. Key information about the microstructure of thin strips under different processes was extracted using electron backscatter diffraction （EBSD）. This information was then deeply integrated with the process data to convert it into a modeling dataset with two-dimensional features. On this basis, the ResNet-CBAM-2D residual neural network model was developed by incorporating the convolutional block attention module （CBAM） into the ResNet18 structure, and the network's hyper parameters were optimized. When the constructed ResNet-CBAM-2D model was compared with other models, the results demonstrated that the ResNet-CBAM-2D model achieved the highest prediction accuracy. The model's coefficient of determination （R²）,mean absolute percentage error （E_MAP）, root mean square error （E_RMS）, and mean absolute error （E_MA） reached 0.980, 3.616%, 15.663 and 15.353, respectively. This model can not only accurately predict the tensile strength of 316 stainless steel thin strips but also predict their yield strength and elongation with high accuracy. The research results provide a new method for the rolling process optimization and product development of stainless steel thin strips, and have important practical value.

The proportion of work rolls scrapped due to spalling when rolling ultra-high-strength steel in the levelling unit of a steel mill was as high as 74.07%, the root cause of which was the uneven distribution of inter-roll forces between the work rolls and the support rolls as well as the concentration of forces in the middle of the rolls. Considering that the unit was also using work rolls of different diameters to roll soft materials at the same time, a collaborative optimization of key parameters of the unit's roll system was carried out. Firstly, the analytical model of plate shape of levelling machine was established, which was applicable to two diameters of work rolls and one diameter of support rolls, and the model could reflect the force situation in two kinds of roll systems. The accuracy of the model was verified by the on-site production data. Next, with typical specifications and steel grades of soft materials as the research object, and with good plate shape quality in the production process of soft materials as the constraint, the depth and width range of the support roll shoulder were pre-optimised within the limit range of bending roll force. Further, taking typical specification and extreme specification ultra-high-strength steel as the research object, the particle swarm optimization algorithm was adopted, with the minimization of contact pressure peak value between rolls and the homogenization of the pressure distribution between rolls as the optimization objective, and on the basis of the pre-optimization of support roll shoulder parameters and within the limit range of bending roll force, the key roll parameters of work roll and support roll were output at the same time, so as to realize the co-optimization of the roll system. Then, the output roll system parameters were brought into the plate shape analysis model, and the optimal bending roll force for different steel grades and specifications was traversed and output with the goal of optimal plate shape quality. Finally, the optimized roll system parameters and bending roll force were substituted into the plate shape analysis model to compare the inter-roll force of ultra-high-strength steel before and after optimization. The results show that the peak inter-roll force is reduced by 26.73% on average, and the uniformity of inter-roll force is improved by 49.98% on average. Through on-site industrial verification, the optimized roll system maintains good plate shape for ultra-high strength steel and soft materials, eliminates work roll spalling accidents, and improves the average tonnage rolled during the roll change cycle from 997 t to 1 231 t. This research offers both theoretical insights and practical engineering solutions for the optimization of roll systems in temper mills operating under multi-steel grade and multi-specification rolling conditions. Its findings are highly significant for enhancing production efficiency and reducing operational costs.

High carbon steel wire rod generally requires Stelmor air-cooling process to have strong cooling capacity, but as the wire size increases, the air-cooling capacity decreases. To determine the influence of wire specifications on air-cooling capacity, wire specifications ranging from ϕ5.5 mm to ϕ18.0 mm were taken as the research object, the air-cooling heat transfer coefficients of different wire specifications were calculated and determined, and the finite element method was used to simulate the air-cooling process of high carbon steel wire. The air-cooling parameters of different specifications of wire before phase transformation, and the influence of wire size and air velocity on the air-cooling effect were analyzed. It has been found that the cooling rate of wire varies greatly in the high temperature stage, and then the cooling rate changes gradually, with a small difference in cooling rate between the inside and outside of the wire. The cooling rate at the beginning of phase transformation is lower than the average cooling rate before phase transformation. The cooling rate at the beginning of phase transformation is power function relationship with wire diameter and linear relationship with air velocity. The center-surface temperature difference at the beginning of phase transformation is linearly related to both wire diameter and air velocity. The cooling rate at the beginning of phase transformation of small-sized wire is relatively high and the temperature distribution on the cross-section is relatively uniform. As the wire size increases, the cooling rate decreases, while the center-surface temperature difference increases, and the effect of enhanced air-cooling deteriorates. When the air velocity is 40 m/s, the cooling rate at the beginning of phase transformation of wires with diameter of 5.5-10.0 mm is larger than or close to the critical cooling rate for pearlite transformation of the studied steel grade. The corresponding cooling rate for large-sized wires with diameter of 12.5-18.0 mm is 14.4-9.0 ℃/s, which is much lower than the critical cooling rate for pearlite transformation, and the air cooling capacity is still insufficient.

Accurate identification of complex multiphase inclusions is critical for the development of environmentally friendly Bi-based free-cutting steels. Traditional metallographic microscopy methods fail to reliably classify and quantify Bi-alloyed free-cutting phases, while existing commercial automated inclusion analysis systems still show limited capability in identifying MnS-Bi composite inclusions with complex morphologies and coexisting bright/dark contrasts. Based on the existing semantic segmentation framework of U-Net neural network and combined with mineral liberation analyzer （MLA）, an automatic image particle analysis system was developed. By exploiting the backscattered electron （BSE） contrast hierarchy （Bi>steel matrix>MnS>silicate） and using MLA data as training masks, the system enabled precise classification of MnS, elemental Bi, and their binary/ternary composite inclusions. Furthermore, by statistically comparing errors with BSE results, an inclusion learning preference was construted to correct errors caused by MLA resolution limitations, thereby improving model accuracy. The system outputs multidimensional quantitative data including inclusion type, size, area, equivalent diameter, and spatial distribution. Statistical analysis reveals that increasing Bi content slightly improves the clustering of inclusions but also promotes their coarsening. Both number and size of elemental Bi particles increase significantly with higher Bi content. Moreover, Bi tends to exist in larger inclusions in the form of Bi-MnS composites. This methodology is not only applicable to current Bi-containing inclusion systems but can also be extended to the intelligent recognition and quantitative analysis of other composite second phases, providing a reliable technical pathway for quantitative characterization and performance optimization of secondary phases in steels.

As an important part of the new energy battery, the battery shell plays an important role in the storage performance and safety performance of the battery. High strength steel for new energy battery pack has gradually become the core shell material of power battery due to its good safety and physical stability, but the problem of performance degradation caused by AlN inclusions needs to be solved urgently. Combined with high temperature test and simulation calculation, the effects of different deoxidation treatments on nitrides in steel were investigated. By scanning electron microscopy and energy dispersive spectroscopy （SEM-EDS）, it is found that the nitrides in the aluminum deoxidized steel are single AlN inclusions and aggregated AlN inclusions. It can be observed that the single AlN is a cubic shape, and the cluster AlN inclusions are sharp. After titanium treatment, the nitrides in the steel are mainly TiN inclusions, which are polygonal or square with angular characteristics. The nitride in the steel after Mg-Ti composite deoxidation treatment exists in the form of MgAl₂O₄-TiN. In addition, the size of AlN inclusions and TiN inclusions in aluminum deoxidized steel and titanium treated steel is generally greater than 5 μm, while the size of MgAl₂O₄-TiN inclusions is mainly concentrated in 1-3 μm. Based on the results of SEM-EDS and Bramfitt's two-dimensional mismatch theory, the mismatch between the related inclusions was calculated. It is found that the minimum mismatch between MgAl₂O₄ and TiN is only 4.08%, while the minimum mismatch between MgAl₂O₄ and AlN is 16.0%, indicating that TiN can heterogeneously nucleate and precipitate on MgAl₂O₄.In addition, combined with the first-principles, the nucleation mechanism of MgAl₂O₄-TiN composite inclusions was revealed, the bulk phase structures of MgAl₂O₄, TiN and AlN were optimized, and the corresponding surface and interface models were constructed. The interfacial energies of MgAl₂O₄, TiN and AlN are calculated to be 3.137 J/m² and 3.596 J / m², respectively, which further indicate that TiN is easier to nucleate on MgAl₂O₄.

The bainite transformation rate in high-carbon steel is relatively slow, so the acceleration of its transformation kinetics is an important research topic. Heating temperature, as one of the key parameters influencing the bainite transformation rate, still gives rise to academic controversies regarding its impact on the bainite transformation. The influence of heating temperature on the bainitic transformation and microstructure in high-carbon Cr-containing bainitic steel was investigated using such methods and equipment as thermal expansion analysis, optical microscope, scanning electron microscope, transmission electron microscope, electron probe microanalysis, and high-temperature laser scanning confocal microscope. The results indicate that under the competing effects of prior austenite grain size and the dissolution of alloying elements, the bainite transformation kinetics of the tested steel decreases with increasing heating temperature. There are numerous micron- and submicron-sized Cr- and Mo-rich carbides in the experimental steel before heating, which dissolve very slowly at lower heating temperatures. Increasing the heating temperature promotes the dissolution of these second-phase particles, thereby increasing the activation energy required for bainite transformation and thus slowing down the transformation kinetics. Furthermore, the effect of heating temperature on bainite transformation has a nonlinear characteristic, and there is a critical temperature beyond which the sensitivity of transformation kinetics to temperature variations is significantly reduced. In addition, due to the segregation of alloying elements and the banded precipitation of second-phase particles, banded distribution of fine-grained and coarse-grained regions is formed in the prior austenite at lower heating temperatures, where the fine-grained regions contain abundant undissolved Cr- and Mo-rich carbides. The bainite formed in the fine-grained austenite regions has shorter length and greater thickness. As the heating temperature increases, the grain size distributions of both the prior austenite and bainite become more uniform.

As ocean engineering extends to deep-sea and polar regions, marine engineering equipment is becoming increasingly large-scale, and the development of ultra-heavy marine engineering steel plates with 690 MPa-grade high strength and -60 ℃ high toughness has become urgent demand. However, with the increase in strength grade and thickness specifications, the impact toughness at the 1/2 thickness （1/2T） position of ultra-heavy plates faces severe challenges. To address this issue, the microstructure and mechanical properties at the 1/4 thickness （1/4T） and 1/2T positions of a 210 mm thick quenched and tempered FH690 ultra-heavy marine steel plate were comparatively studied, aiming to reveal the correlation between the microstructure and low-temperature toughness of ultra-heavy plates from a crystallographic perspective. Results show that the tensile properties of 210 mm thick FH690 industrial trial steel plate are similar at the 1/4T and 1/2T positions, the yield strengths are 776 MPa and 767 MPa respectively, the tensile strengths are 850 and 856 MPa respectively, and the elongations after fracture are 20.5% and 21.6% respectively. Additionally, the results of series temperature impact tests show that although the upper shelf impact energy at 1/4T position （about 141 J） is higher than that at 1/2T position （about 109 J）, the ductile-brittle transition temperatures （DBTT） of the two positions have little difference, being approximately -78 ℃ and -73 ℃, respectively. Scanning electron microscopy （SEM） analysis shows that the microstructures at both the 1/4T and 1/2T positions are tempered lath bainite, with fine spherical carbides dispersed in the bainite matrix. Transmission electron microscopy （TEM） analysis further confirms that these fine carbides are mainly M₂₃C₆-type precipitates with size of approximately 100 nm. Crystallographic characteristic analysis shows that the prior austenite grains at 1/4T position are smaller than those at 1/2T position, while the block boundary density at 1/2T position is significantly higher than that at 1/4T position. Instrumented impact tests show that at -80 ℃ near the DBTT, the crack initiation energies at 1/4T and 1/2T positions are similar （27 J and 30 J respectively）, while the crack propagation energy at 1/4T position is significantly higher than that at 1/2T position. This finding indicates that high density of high-angle block boundaries helps maintain crack initiation energy and lower the ductile-brittle transition temperature during low-temperature impact, whereas fine prior austenite grains significantly enhance crack propagation energy.

Hydrogen metallurgy introduces hydrogen as a reducing agent and a fuel in the reduction smelting process of iron, and it has attracted widespread attention due to its ability to utilize low-grade iron ore, replace carbon reduction in the steel industry, and enable low-cost preparation of high-purity iron. High-purity products obtained through pure hydrogen metallurgy exhibits extremely low carbon content, high purity, and excellent corrosion resistance. Extreme low-carbon experimental steel was prepared using high-purity iron obtained through hydrogen metallurgy as the raw material. The microstructural characteristics and mechanical properties of the extreme low-carbon steel with different Ni-Cu contents were studied by OM（optical microscope）, SEM（scanning electron microscope）, EBSD（electron backscatter diffraction）, and TEM（transmission electron microscope）. The results show that adding Ni and performing controlled recrystallization-rolling refines the rolled microstructure, leading to equiaxed ferrite with an average grain size of 20 μm. Furthermore, the higher the Ni content, the more obvious the grain refinement effect. Nanoscale Cu-rich precipitates are formed by adding Cu and conducting quenching and tempering heat treatment. The strength of 2NiCu steel is more than 400 MPa higher than that of high-purity iron as a result of multi-strengthening mechanisms, including solution strengthening, refinement strengthening, and precipitation strengthening, with a yield stength of 573 MPa and a tensile strength of 673 MPa. In addition, the elongation of 2NiCu steel is higher than 25%. The reason for the poor toughness of heat-treated 2NiCu steel is investigated, and it is attributed to the Cu-rich precipitates with a face centered cubic （FCC） structure. The hard Cu-rich phase is noncoherent with the soft matrix, resulting in the obstruction of dislocation movement and stress concentration during the deformation process.

The treatment of blast furnace slag through dry centrifugal granulation process with waste heat recovery can overcome the problems of the water quenching method and thus can hopefully become the promising blast furnace slag treatment process in future. However, the issues of easy stick to the equipment walls by the half-molten slag particles after granulation and other issues have led to the fact that this process has not yet been industrially applied. Focusing on solving these issues, a zig-zag shaped counter-current heat exchanger was adopted to combine with the centrifugal granulation of molten slag to enhance the cooling of slag particles, and three-dimensional computational fluid dynamics （CFD） model of motion and heat transfer of high-temperature slag particle swarms in both the centrifugal granulation chamber and the heat exchange chamber was developed to analyze the critical parameters influencing the heat transfer of multi-sized slag particles and to numerically simulate the motion and heat transfer behaviors of the particles. On the basis of the numerical simulation results, the motion and heat transfer behavior of the particle swarms inside the zig-zag counter-current heat exchange chamber beneath the granulation chamber was further investigated. The impact of various process parameters on the particle heat transfer was investigated as well, and the chamber's structural dimensions were subsequently optimized. Numerical simulation results indicate that, particle size mostly alters the heat exchange of particle swarms by altering the specific surface area of particles and external heat exchange conditions. Particle bond can be successfully reduced and the residence time of the particles in the heat exchanger chamber extended through improvement of centrifugal granulation process using zig-zag counter-current heat exchangers. The optimum slag particle entrance width of the zig-zag counter-current heat exchanger is 200 mm and the cooling airflow velocity is 0.08 m/s. The findings of this study are of great significance for the industrial application of centrifugal granulation and waste heat recovery technology from molten slag.

In order to alleviate the existing cementitious capillary crystalline waterproof （CCCW） materials relying on the status quo of high-cost raw materials, and to promote the resource utilization of blast furnace slag and fly ash. A complete powder formulation design was innovatively adopted based on the component characteristics of the Prova waterproof type （PW） active substance, an active system consisting of hydroxycarboxylic acid/aminocarboxylic acid composite complexing agent, potassium sulfate/calcium sulfate composite expansive agent, and carbonate/silicate composite precipitant was systematically constructed. The CCCW was prepared using ordinary silicate cement and quartz sand as matrix materials, and was synergized with blast furnace slag powder-fly ash composite powder to construct a multifaceted cementitious system. Ratio optimization was carried out using an orthogonal design combined with the efficacy coefficient method. A represents the complexing agent composite powder, referring to the mass ratio of hydroxycarboxylic acid complexing agent （a₁） to aminocarboxylic acid complexing agent （a₂）. B represents the composite expansion agent powder, referring to the mass ratio of potassium sulfate expansive agent （b₁） to calcium sulfate expansive agent （b₂）. C represents the precipitating agent composite powder, referring to the mass ratio of carbonate precipitant （c₁） to silicate precipitant （c₂）. D represents the blast furnace slag-fly ash composite powder, referring to the mass ratio of fly ash （d₁） to blast furnace slag powder （d₂）. By comprehensively evaluating the 28 d flexural strength, 28 d compressive strength, impermeable pressure of coated mortar, impermeable pressure of mortar after coating removal, and bond strength to wet substrate, the optimal combination was determined to be A = 2∶3, B = 4∶1, C = 3∶2, and D = 2∶3. The performance parameters of the optimum specimen L8 under the best ratio are, 28 d flexural strength is 8.36 MPa, 28 d compressive strength is 34.16 MPa, representing improvements of 10.1% and 62.9% respectively compared to PW, impermeable pressure of coated mortar is 1.3 MPa, impermeable pressure of mortar after coating removal is 1.0 MPa, bond strength to wet substrate is 1.08 MPa, an increase of 7.8% compared to PW, and compliant with national standards. The complexing agent reacts with Ca²⁺ in concrete by complexing with Ca²⁺, and the soluble calcium complex generated diffuses to the inside of the concrete under the action of moisture, and re-releases Ca²⁺ at cracks or pores, and then reacts with CO₃²^-, SiO₃²^-, etc. generates C—S—H gel network, which plugs the pores and repairs the cracks, expansion agent generates moderate volume expansion during hydration and squeezes the capillary pores and microcracks, precipitant provides CO₃²^-, SiO₃²^-, etc., which combines with Ca²⁺ and generates precipitates, which directly fills the cracks. A large amount of CaO and SiO₂ in blast furnace slag powder and fly ash are hydrolyzed in the alkaline pore liquid, releasing Ca²⁺ and SiO₃²^-, which promot the formation of C—S—H gel network. The results provide a new path for the efficient resource utilization of blast furnace slag and fly ash in waterproofing materials.

The rotary hearth furnace treatment process for metallurgical dust is the main disposal process adopted in the steel industry at present. However, in the actual production process, the problem of uneven reduction roasting often occurs. A detailed visual and data-based analysis of non-uniformity issue in the reduction roasting of metallurgical dust by combining microscopic scanning electron microscopy（SEM） analysis with macroscopic Maps statistical analysis was conducted. The results show that the metallization rate of roasted pellets reaches 89.04%, the dezincification rate reaches 81.66% and the compressive strength reaches 3.03 kN under the conditions of roasting temperature 1 250 ℃ and roasting time 15 min, meanwhile the metallization rate and the dezincification rate of roasted pellets increase further with the increase of roasting temperature and the extension of roasting time. However, the compressive strength of roasted pellets gradually decreases while the roasting time is too long. The Maps statistical analysis of roasted pellets shows that increasing the roasting temperature is more conducive to improving the reduction degree of outer circle and bottom part of roasted pellets, and extending the roasting time is also more beneficial to improving the reduction degree of the bottom part of roasted pellets, but the effect on reduction degree of inside and outer circle of roasted pellets is relatively similar. Meanwhile, the increase of roasting temperature is also more conducive to enhance the densification of bottom part of roasted pellets and reduce the non-uniformity of pore structure between the top and bottom parts of roasted pellets, and thereby significantly improve the overall compressive strength of roasted pellets. However, an excessively long roasting time will cause the small pores in the roasted pellets to fuse into large pores, which will instead reduce the compressive strength of roasted pellets. Furthermore, the silicate （slag phase） and wüstite （Fe_xO） in the roasted pellets are more prone to fracture, while the metal iron （Fe） can delay the crack propagation. Therefore, appropriately increasing the metallization rate of roasted pellets and reducing the content of silicate （slag phase） is beneficial for enhancing the compressive strength. Based on Maps statistical analysis, the study explores the change patterns of phases and pores during the reduction roasting process of metallurgical dust. The analysis results can provide guidance and suggestions for the production practice of treating metallurgical dust with the rotary hearth furnace process.

The iron and steel industry is a significant sector in global carbon emission governance, characterized by a large total carbon emission volume, high intensity, and difficulty in reducing carbon emissions. To smoothly achieve the "dual carbon" goals, it is extremely urgent for iron and steel enterprises to carry out low-carbon transformation. The low-carbon transformation of the iron and steel industry is systematic project that requires the joint participation of various social elements. Among them, transition finance plays an important role as a facilitator in this process. In addition, the financing characteristics and demands of different types of iron and steel enterprises （state-owned enterprises/private enterprises, blast furnace-basic oxygen furnace/scrap electric are furnace, listed/unlisted） vary, and the channels and difficulty levels of obtaining financial resources also differ. Based on thorough research and interviews to different types of iron and steel enterprises and financial institutions, the current situation and existing problems of transition finance supporting the low-carbon transformation of different type iron and steel enterprises at the present stage were summarized and sorted, and put forward targeted suggestions and opinions. The results show that the role of transition finance has not been fully unleashed at the present stage, and there is a lack of unified national directory and implementation standards for transition finance. The proportion of green indicators in transition finance tools is relatively low, and their innovation needs to be improved urgently. Furthermore, the transition finance tools have not effectively matched the demands of iron and steel enterprises. Private Scrap-EAF（scrap-electric arc furnace） iron and steel enterprises that need more financial support find it more difficult to obtain transition finance than state-owned BF-BOF（blast furnace-basic oxygen furnace） enterprises, presenting a situation of "adding the finishing touch" rather than "providing timely assistance". Problem-oriented, following suggestions are put forward, establish a national unified directory, special statistics and incentive mechanism for transition finance, strengthen the interaction between industry and policy, broaden the diversified financing channels for steel enterprises, and innovate and promote credit enhancement and risk-sharing tools.

The global metallurgical industry produces about 3.2 billion tons of mineral streams annually （including tailings and slags, etc.）, with industrial carbon emissions accounting for 25% of the total. The traditional steelmaking presents a binary opposition linear model of "ferrous stream-solid waste stream", which forcibly separates the mass and heat properties of metallurgical slag, resulting in the low-end and low-efficiency utilization of existing metallurgical slag resources.To address these contradictions and challenges, the theoretical concept and framework of "metallurgical derived mineral stream （MDMS）" was proposed. Guided by metallurgical process engineering theory, it broke through the traditional single-core ferrous stream model, constructed a "mass-heat-structure" collaborative regulation system, and realized efficient utilization of mass and heat resources of metallurgical high-temperature slag, directional regulation of mineral phases and online productization path. Based on mesoscale engineering regulation theory, combined with thermodynamic phase equilibrium models and online regulation strategies, a trinity technical system integrating composition, structure and energy was developed. Process schemes for blast-furnace and converter slags were designed, along with the development of key equipment such as slag conditioning reactors, gradient cooling towers, and online separation devices, forming a high-value-added mineral building material product chain, and it was planned to realize global promotion and standardization. Engineering practices demonstrate that MDMS breaks through the paradigm of "end-of-pipe treatment", improving the resource utilization rate of metallurgical slag to 92%. Verified by life cycle assessment （LCA）, this technology reduces carbon emissions per ton of steel by 0.6-0.8 t. Blast furnace slag-based online mineral wool （thermal conductivity no less than 0.042 W/（m·K）） and converter steel slag asphalt aggregate （crushing value no less than 12%） exhibit significant technical and economic advantages. Moreover, MDMS system demonstrates remarkable economic viability, and the payback period of system investment is shortened to 3.2 years, which provides another technical path and a reference solution for the coordinated low-carbon transformation of steel, building materials, chemicals and other industries.