15 November 2025, Volume 60 Issue 11

    

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Technical Reviews
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  Research status and development pathways of multi-process coupling mechanisms in non-quenched and tempered steel 46MnVS5

  DING Zhijun, WANG Xiangcui, WANG Shuhuan, ZHANG Yanchao, XUE Yuekai, ZHAO Dingguo

  Iron and Steel. 2025, 60(11): 1-20. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250310

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  Under the background of global "dual-carbon" strategy, non-quenched steel 46MnVS5 has become a key material for automotive lightweight manufacturing due to its low-carbon, environmentally friendly, energy-saving and high-efficiency features. The process control and optimization strategies of 46MnVS5 steel in the whole process of refining-continuous casting-rolling are systematically reviewed. The microalloying design, regulation mechanism of organization and properties and bottlenecks of industrial application are analyzed emphatically. The results show that through the synergistic effect of V-Ti-Nb composite microalloying and controlled-rolling and controlled-cooling technology （thermo-mechanical control process, TMCP）, the precise regulation of ferrite-pearlitic organization can be realized, so that the material can reach the strength of 800 MPa level under the condition of no heat treatment, and the energy consumption and CO₂ emission can be significantly reduced. Aiming at the three core problems in the production process, sulfide inclusion control in the refining process, central segregation suppression in the continuous casting process, and organization uniformity enhancement in the rolling process, the whole chain solution of "composition design-solidification control-deformation strengthening" is proposed. Experiments show that the optimized process can improve the strong plasticity of 46MnVS5 steel by 15% and fatigue life by 2 orders of magnitude. At the application level, the engineering practice of 46MnVS5 steel in expanded connecting rod, steering knuckles is discussed in detail. The breaking rate is stable at more than 98%, which fully meets the stringent requirements of high-end engines such as EA888. The future development direction will focus on the intelligent optimization of process parameters based on machine learning, the mechanism of rare earth microalloying on the modification of inclusions, and the design of ultra-high strength toughening for chassis parts of new energy vehicles. It provides theoretical support and technical routes for the development of a new generation of green non-quenched and tempered steel.
  
Raw Material and Ironmaking
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  Preparation of biomass carbon-containing spheres and effect of n（C）/n（O）on their self-reduction

  LI Dongdong, FENG Haichao, CHAI Yifan, LIU Peijun, LIU Wenying, HU Wenxian

  Iron and Steel. 2025, 60(11): 21-31. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250314

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  In order to meet the urgent needs of the green and low-carbon transformation of the iron and steel industry, a new type of carbon-containing pellets with renewable biochar as carbon source was developed. Carbon-containing pellets can significantly reduce energy consumption and carbon emissions in traditional smelting processes due to their excellent self-reduction characteristics, high reaction efficiency and high energy utilization. The use of biomass as a low-carbon resource to replace fossil fuel-based carbon sources is expected to further reduce the carbon footprint of ironmaking. Biomass carbon-containing pellets were prepared by hot pressing. The effects of hot pressing temperature, hot pressing time, hot pressing pressure and raw material ratio on the strength of carbon-containing pellets were systematically investigated. The dynamic evolution of weight loss rate and compressive strength during the self-reduction process for pellets with different n（C）/n（O） ratios was studied, along with their internal relationship. The results show that the optimum preparation parameters of hot-pressed biomass carbon-containing pellets are as follows, hot-pressing temperature of 300 ℃, hot-pressing pressure of 40 MPa, hot-pressing time of 3 min, and binder content of 6% . The pellet strength meets blast furnace entry requirements. Pellets strength decreases with increasing carbon-oxygen ratio. Pellets with n（C）/n（O） of 0.4 exhibit the highest strength （2 653 N）, while those with n（C）/n（O） of 0.8 show the lowest （2 013 N）. During self-reduction, the compressive strength of all pellets decreased significantly before increasing sharply. The n（C）/n（O） of 0.6 pellets demonstrated the most typical behavior. When the weight loss rate reached 31.8%, the strength valley value dropped to 292 N due to structural loosening, but surged to more than 2 500 N at 36.05% weight loss because of iron crystals formation,and supporting the green transformation of the steel industry.
  
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  Cold-pressed forming and properties of vanadium nitride finished product scraps

  TANG Jianzhong, WU Enhui, TANG Xiaojing, LI Jun, HOU Jing, XU Zhong, ZHANG Yuan, LI Hong

  Iron and Steel. 2025, 60(11): 32-42. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250291

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  To enhance the recycling efficiency of qualified-composition but morphologically defective vanadium nitride （VN） finished product scraps generated during rotary kiln production, polyvinyl alcohol （PVA） was employed as a binder to prepare VN cold-pressed pellets via cold-pressing. Orthogonal array testing investigated the effects of binder ratio, mass fraction, water distribution ratio, and forming pressure on the drop strength and compressive strength of cold-pressed pellets. A single-factor experiment on particle size explored its regulatory mechanism on pellet density. The orthogonal experimental results demonstrated that, for green pellets, binder ratio was the dominant factor affecting drop strength while forming pressure governed compressive strength. For dried pellets, binder concentration primarily controlled drop strength whereas binder ratio determined compressive strength. Dried pellets exhibited significantly higher drop strength and compressive strength compared to green pellets, primarily because the drying process concentrates and solidifies the binder into a three-dimensional network structure, forming rigidly interlinked solid bridges between VN particles. The water distribution ratio exhibited a negative correlation with both the drop strength and compressive strength of green pellets and dried pellets, with both strengths decreasing as the water distribution ratio increased. The optimal process parameters obtained were as follows, binder ratio of 12%, mass fraction of 8%, water distribution ratio of 0 , and forming pressure of 9 MPa. Under these conditions, the average drop strength and compressive strength of green pellets were 13 times/（0.5 m） and 139 N/pellet respectively, while those of dried pellets were 125 times/（0.5 m） and 866 N/pellet respectively, with the density of dried pellets being 2.82 g/cm³. Using the optimized molding process parameters, a single-factor experiment on particle size was conducted. The results showed that the density of dried pellets gradually increases with decreasing particle size. When the particle size distribution is d₁₀ = 2.730 µm （where d₁₀ indicates that 10% of the particles volume fraction have a diameter smaller than this value）, d₅₀ = 7.359 µm （where d₅₀ indicates that 50% of the particles volume fraction have a diameter smaller than this value）, and d₉₀ = 50.235 µm （where d₉₀ indicates that 90% of the particles volume fraction have a diameter smaller than this value）, the drop strength and compressive strength of dry pellets reached 125 times/（0.5 m） and 1 019.5 N/pellet, and the density increased to 3.10 g/cm³. This fully satisfies the physical property requirements for pellets charged into the furnace specified.
  
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  Influence of different reducing gases on direct reduction process of gas-based shaft furnace

  SHEN Fengman, WANG Shuo, ZHANG Yan, PAN Xiangyang, ZHENG Haiyan, LI Tao, YUAN Wanneng

  Iron and Steel. 2025, 60(11): 43-50. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250311

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  To achieve the "dual carbon" strategy, various energy-saving and emission-reduction measures and processes have been adopted in the ironmaking field. Based on domestic resource conditions, the coke-oven-gas（COG）-based shaft furnace process has been successfully developed. However, the composition change of the reducing gas phase inside the shaft furnace in the process remains unclear. Therefore, a method for accurately characterizing the reducing gas phase composition was designed and systematically investigated of the effects of four factors, including the type of filled materials （Al₂O₃ pellets, low-reducibility oxidized pellets, high-reducibility oxidized pellets, pre-reduced pellets）, the type of the reducing gas, natural gas （NG） ratio, and reduction zone temperature on the gas phase composition, effective CH₄ conversion ratio, and carbon deposition amount under different process conditions. Under the same conditions, the order of CH₄ conversion ratio is Al₂O₃ pellets<low reducing oxidized pellet<high reducing oxidized pellet<pre-reducing oxidized pellets; With the increase of NG ratio, the gas-phase reduction potential （H₂+CO） significantly decreases, the reduction degree （R_t） of pellets decreases, the CH₄ conversion ratio decreases, the carbon deposition amount per unit time in the system significantly increases, and the NG ratio should not exceed 30%. When the reduction zone temperature reaches above 900 ^oC, increasing reduction zone temperature causes the total amount of the effective gas at the outlet basically unchanged, but the carbon deposition amount per unit time increases, therefore, the reduction zone temperature in the shaft furnace should be controlled between 900-1 000 ℃.
  
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  Preparation and industrial application of steel-copper-steel composite cooling stave for blast furnace

  LIU Xudong, JIAO Kexin, ZHANG Jianliang, ZONG Yanbing, GUO Ziping, YANG Xiduan, LIU Yanxiang, SHAN Songjian

  Iron and Steel. 2025, 60(11): 51-60. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250341

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  The cooling staves in high-heat-load zones of the blast furnace, such as the belly and bosh, are subjected to long-term mechanical wear from burden materials, chemical erosion from slag and hot metal, and high-temperature thermal stress impact. Their service life has become a key factor restricting the long campaign life of blast furnaces. Traditional ductile cast iron cooling staves struggle to meet the demands of intensified smelting due to insufficient thermal conductivity. Although copper cooling staves possess excellent thermal conductivity, their low strength and poor wear resistance limit their service life to typically 6-8 years, failing to meet the modern blast furnace target of over 15 years. To address this situation, a novel steel-copper-steel composite cooling stave is designed and developed , which has undergone industrial application trials in the bosh area of a 2 800 m³ blast furnace. This cooling stave features a "sandwich" structure,a 5 mm hot-face steel layer, a 58 mm copper layer, and a 22 mm cold-face steel layer. These dissimilar materials are metallurgically bonded via two explosive welding processes, combining the high thermal conductivity of copper with the high strength and wear resistance of steel. The trial results demonstrate that this composite structure significantly extends the service life of the cooling stave. Its maximum annual wear rate is only 3.06 mm/a, which is just 32.7% of that of copper-steel composite cooling staves and 25.9% of that of traditional copper cooling staves. The cooling water pipes showed zero wear, and the dovetail groove structure remained intact. The mechanism analysis shows that the high temperature exposure, furnace charge wear and thermal expansion extrusion caused by slag peeling are the main mechanisms of stave failure, and the hot surface steel layer is helpful to promote the formation and condensation of slag skin and effectively delay the wear of the waist-hearth transition zone. The new cooling stave significantly improves the wear resistance and service stability of the high heat load area by optimizing the structure, so that it has high thermal conductivity, deformation resistance and excellent wear resistance. It provides a new path for the optimization of the cooling stave in the high heat load area of the blast furnace, which is of great significance and popularization value to promote the energy saving and carbon reduction of the iron and steel industry and realize the safe and long-life operation of the blast furnace.
  
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  Data and mechanism integrated digital twin of rotary kiln

  WANG Yaozu, LIU Zhengjian, ZHANG Jianliang, DAI Zhangjie, XU Yue

  Iron and Steel. 2025, 60(11): 61-71. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250322

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  As a core equipment for high-temperature material processing （such as metallurgical roasting, cement calcination, and solid waste treatment）, the precise distribution of the internal temperature field and the real-time state of the kiln wall thickness in rotary kilns directly determine product quality, energy consumption levels, and operational safety. However, under the harsh conditions of high temperature, rotation, enclosure, and fluctuating working conditions, existing detection methods struggle to penetrate the kiln body to achieve three-dimensional dynamic visualization of the internal temperature field, nor can they continuously monitor the erosion and thickness changes of the refractory lining in real time. Therefore, constructing a digital twin of the rotary kiln that integrates multi-source data to dynamically map and predict the evolution of the internal temperature field and the distribution of kiln wall thickness is key to process optimization, energy efficiency improvement, extending kiln lifespan, and safety warnings. It also represents a common technical challenge in the intelligent upgrading of process industries that urgently needs to be addressed. This study proposes, for the first time, a method for constructing a rotary kiln digital twin based on the integration of data and mechanism, incorporating core technologies such as real-time three-dimensional temperature field simulation, wall thickness monitoring models, and reduced-order models. Within a multi-physics coupling framework, the study systematically and deeply considers complex processes such as pulverized coal combustion and pellet oxidation reactions, achieving high-precision simulation of the internal temperature field distribution in the rotary kiln. A machine learning-based reduced-order model for the rotary kiln temperature field is proposed, enabling real-time simulation and prediction of the kiln's internal temperature field. Additionally, by integrating laser scanning technology with heat transfer theory, the system achieves precise monitoring of the rotary kiln's inner wall thickness and ring formation. Rigorous field experiments confirm that the proposed digital twin soft-sensing method demonstrates outstanding performance in predicting the internal temperature field distribution and wall thickness conditions of the rotary kiln. The prediction deviation of the kiln's internal temperature is controlled within approximately 1% （<5 ℃）, while the accuracy rate for kiln wall thickness prediction reaches a high level of 90%. The spatial resolution for positioning temperature measurement points and detecting wall thickness achieves centimeter-level precision on the kiln body. This research provides timely and accurate feedback and guidance for on-site production, holding significant practical application value and offering a new paradigm for the construction of metallurgical digital twins.
  
Steelmaking
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  Formation and control of large size inclusions in GCr15 bearing steel

  XU Jianfei, YU Qingcheng, YANG Pu, ZHAO Yang

  Iron and Steel. 2025, 60(11): 72-82. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250358

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  Large size inclusions have a significant effect on the fatigue life of bearing steel. 25 industry trials of the BOF-LF-RH-CC process were conducted to control the large size inclusions in GCr15 steel. ASPEX scanning electron microscope was used to analyze the composition of inclusions. The high-frequency water immersion testing was used to detect, locate and dissect the inclusions. There are mainly two types of large size inclusions in bearing steel. The first type of large size inclusions is the calcium aluminate with low melting point, and some small size MgO·Al₂O₃ inclusions precipitate in these large size calcium aluminate inclusions. The emulsification of the refining slag is the mainly source for these inclusions. Reducing the basicity of refining slag can better control this kind of inclusions. Adding SiC and FeSi in tapping process for deoxidation and the Al content of molten steel was adjusted in the LF refining process can significantly reduce the basicity of refining slag. The second type of large size inclusions is calcium aluminate and MgO·Al₂O₃ with high melting point, which is related to the clogs of the submerged entry nozzle. Many high melting point inclusions, which were easy to adhere to the surface of the nozzle, were still detected in the steel in the tundish when the molten steel was slightly oxidized, for example the total oxygen mass fraction of molten steel only increases by 0.000 08% to 0.000 10% although the inclusions were mainly low melting point calcium aluminates after RH vacuum. Therefore, controlling the oxidation degree of molten steel and reducing the number of newly generated high-melting point inclusions in the tundish can better control this type of inclusions.
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  Effects of SiO₂ on Al content and inclusion characteristics in H13 steel during electroslag remelting

  SUN Xiaolin, ZHONG Qingyuan, WANG Ningfei, FENG Xuan, ZHENG Chunyu, CUI Limin, LI Minggang, XU Dong

  Iron and Steel. 2025, 60(11): 83-94. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250331

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  Silicon loss and aluminum pick-up occur in H13 steel after gas-protective electroslag remelting （PESR）. The influence of SiO₂ content in slag on the steel composition and inclusion characteristics in H13 after PESR was analyzed. The result shows that oxygen mass fraction has all been reduced within 0.001 2% after PESR and the types of oxide inclusions remains unchanged, primarily consisting of CaO（-MgO）-Al₂O₃ and MgO·Al₂O₃ spinel. When the S1 slag with low SiO₂ content is used during PESR process, the bottom sample of the steel shows high aluminum pick-up as much as 0.109 percent point. There are main CaO（-MgO）-Al₂O₃ inclusions at the bottom of H13 steel after PESR, of which some exhibits low melting points and big size larger than 10 μm. The proportion of MgO·Al₂O₃ spinel inclusion in the bottom of the steel after PESR is low, and the average size of the oxide inclusion is increased from 4.8 μm in the electrode to 8.1 μm. In addition, a lot of agglomerated AlN particles are observed only in this bottom sample. The increase in Al mass fraction at the top of the steel is small after PESR, and there are mainly small-sized MgO·Al₂O₃ inclusions. Therefore, the oxide inclusion at the top of H13 steel is smaller than those at the bottom. A quantity of （Ti,V）（C,N） carbonitrides is also observed at the top samples. The agglomerated AlN and large size CaO（-MgO）-Al₂O₃ result in a deterioration of the cleanliness of H13 steel after PESR. Based on the ion and molecule coexistence theory （IMCT） of molten slag and thermodynamic equilibrium of the [Si]-[Al] reaction in steel, it is determined that （Al₂O₃） in the slag can be reduced by [Si] in the molten steel, when the temperature is larger than 1 457 ℃ as using S1 slag during the electroslag remelting of H13 steel, thereby increasing the aluminum content in the remelted steel. Increasing the （SiO₂） content in slag and reducing the temperature can effectively suppress aluminum pick-up from the slag into the steel. According to thermodynamic analysis, the AlN observed at the bottom sample EB1 of the steel can be formed during the solidification process, and the equilibrium dissolution temperature is as high as 1 322 ℃, which can be retained in the die steel after forging. The increase in Al mass fraction is decreased to 0.017 percent point at the bottom of H13 steel after PESR when S2 slag is used with the increased SiO₂ content, significantly suppressing the aluminum pick-up and AlN formation during PESR process. It also reduces the variation of aluminum content between the top and bottom part of the remelted steel, and decreases the size of oxide inclusions. However, low-melting-point CaO（-MgO）-Al₂O₃ inclusions persists in the H13 steel even after PESR using S2 slag. It is deduced that this type of inclusion is difficult to be absorbed and removed by the molten slag during PESR process. Meanwhile, the inclusions with low melting point are liable to agglomerate and form large-sized inclusions, which ultimately deteriorates the performance of the die steel. The contents of aluminum and calcium in the steel have an influence on controlling the inclusion during PESR, as well as the types of the inclusion in the electrode.
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  Three-dimensional thermo-mechanical coupling model of strand in whole process of slab continuous casting and its application

  ZHU Guoming, YU Lin, ZHAO Peilin, TAO Tao, WANG Yongming, KANG Yonglin

  Iron and Steel. 2025, 60(11): 95-111. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250272

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  In the continuous casting process, multiple metallurgical physical phenomena such as molten steel solidification, heat and mass transfer, fluid flow, and solid deformation are dynamically coupled, forming a complex nonlinear system. Multiple stress fields, including phase transformation stress, thermal stress, ferrostatic pressure, and mechanical forces （support roll contact force, bending, and straightening forces）, are nonlinearly superimposed and synergistically affect the casting strand. During long-term operation, the strand exhibits characteristics such as low strain rates, wide temperature ranges, and steep gradients, resulting in high complexity in the spatial distribution and temporal evolution of its temperature and stress fields. The continuous casting of 230 mm×1 930 mm slabs was focused on, liquid molten steels assumed to have negligible deformation resistance,gap heat exchange （strand-mold copper plate） and convective heat exchange （strand-secondary cooling spray） were equivalently simplified as contact heat conduction to systematize heat exchange boundaries,the strand model incorporated preset parameters such as pour temperature. After detailed verification and elaboration of key technical aspects including the thermo-mechanical coupling algorithm, material model construction, and equivalent simplification of heat exchange boundaries in primary/secondary cooling zones, a full caster finite element model was established. This enabled successful 3D（three-dimensional） thermo-mechanical coupling numerical simulation of the entire continuous casting process. Analysis of computational results reveal the spatiotemporal evolution and distribution characteristics of the strand's temperature field, stress-strain field, shell thickness, and solidification front morphology. An effective simulation method for holistic strand behavior analysis is provided, an in-depth study of stress-related slab defect formation mechanisms is facilitated, and references for optimizing caster design and production processes are offered.
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  Analysis of internal flow field characteristics of secondary cooling air-water nozzle based on inlet pressure control

  HE Xin, WANG Huisheng, CUI Henan, ZHANG Jiangshan, CHEN Linheng, LI Ming, GUAN Min, LIU Qing

  Iron and Steel. 2025, 60(11): 112-122. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250324

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  Spray cooling is the primary cooling method in the secondary cooling zone of continuous casting. The spray nozzle jet behavior directly affects the spray cooling efficiency, which in turn impacts the quality of the continuous casting billet. Taking the air-water fan-shaped nozzle used in continuous casting of square billets at a certain steel mill as the research object, a nozzle jet simulation model was constructed, the changes influence of air and water pressure at the nozzle inlet on the fluid velocity, turbulent kinetic energy, and vortex distribution inside the nozzle was investigated, the key factors affecting the stability of water flow at the nozzle outlet was revealed, and corresponding control methods was proposed. The results show that when the water pressure increases by 0.10 MPa from 0.10 MPa to 0.30 MPa, the initial velocity of liquid phase gradually increases, with values of 2.43, 5.45, and 9.17 m/s, respectively. The distance from the nozzle water inlet to the maximum velocity position of liquid phase inside the nozzle is 35, 29, and 25 mm, respectively, and the corresponding gas-liquid two-phase velocity gradient gradually decreases. The liquid phase viscous force increases, and the average turbulent kinetic energy decreases, with values of 367.66, 142.43, and 96.87 m²/s². The central large vortex inside the nozzle gradually decreases, and the small vortices near the nozzle wall gradually disappear. The variation coefficient of water flow rate at the nozzle outlet decreases from 0.533 to 0.505 and 0.489, respectively, which is beneficial for improving the stability of flow rate at the nozzle outlet. When the gas pressure increases by 0.05 MPa from 0.10 MPa to 0.20 MPa, the initial velocity of liquid phase first decreases and then increases, with changes of 2.44 m/s and 1.22 m/s, respectively. The position of the maximum liquid phase velocity within the nozzle remains unchanged, with the maximum liquid phase velocity first increasing by 1.59 m/s and then decreasing by 1.85 m/s. The average turbulent kinetic energy gradually increases, with values of 165.21, 367.66, and 598.90 m²/s². The central large vortex within the nozzle expands or splits into multiple medium-sized vortex clusters, and the number of small vortices increases and they migrate toward the center. The variation coefficient of water flow rate at the nozzle outlet increases from 0.514 to 0.533 and 0.575, and the stability of flow rate at nozzle outlet decreases. It is concluded that when the water pressure is 0.30 MPa and the air pressure is 0.10 MPa, the stability of flow rate at the nozzle outlet is optimal, providing theoretical and data support for the regulation of the secondary cooling process in continuous casting.
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  Effect of molten steel upward flow on slag-metal interface in argon-blown mold

  LI Pengfei, TAO Mengle, JIANG Yan, RONG Wenjie, HUO Yueqin, LI Baokuan

  Iron and Steel. 2025, 60(11): 123-133. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250360

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  In the continuous casting mold, the upward flow of molten steel directly affects the intensity of slag-metal interface fluctuations, where interface stability determines the surface quality of cast slabs and production efficiency. The influence mechanism of molten steel upward flow on slag-metal interface behavior under argon blowing conditions was investigated, providing a theoretical basis for addressing issues like slag entrainment, secondary oxidation, and inclusion defects caused by excessive interface fluctuations. A three-dimensional mathematical model of a 1 300 mm×230 mm slab continuous casting mold was established to simulate how the positions of the narrow-face jet impingement point and upward flow vortex core vary with argon flow rates （0, 5.0, 7.5, 10.0 L/min） and their effects on interface behavior.Conclusion shows that without argon blowing, shear forces from upward flow create significant waving heights （peaking at 14 mm） near the narrow face. Increasing argon flow intensifies interface fluctuations near the submerged entry nozzle （SEN） while causing the impingement point to rise from 396.5 mm to 345.3 mm due to argon bubble disturbances. This upward shift weakens shear forces of upward flow an slag-metal interface, reducing wave heights and velocities near narrow face to mitigate slag entrainment risks. Bubble disturbances moderately balance jet energy dissipation without excessive SEN fluctuations with the argon flow rate of 7.5 L/min（impingement point is 355.6 mm）. The vortex core exhibits notable width-direction displacement （15 mm from symmetry plane） under argon blowing but remains stable elsewhere. Vertically, vortex cores gradually descend with distance from the symmetry plane, indicating kinetic energy decay. At the same time, waving height in narrow face decreases in the direction away from the central symmetry plane,and significantly increases near SEM,close to central symmetry plane.This phenomenon splits upward flow paths, creating multi-peak velocity distributions near the SEN under multi-vortex and bubble interactions. At 10 L/min, the strongest main peak and lowest standard deviation demonstrate optimal vortex-bubble synergy. This study reveals the influence mechanism of the upward flow of molten steel on the fluctuation of slag-metal interface in the continuous casting mold under argon blowing conditions, and provides a theoretical basis for optimizing the process and improving the quality of cast slabs.
Metal Forming
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  Strip shape prediction model for cold rolling 18-roll mill

  ZHANG Ji, WANG Zhixuan, ZHU Jiahao, ZHU Sihua, LI Sufang, BAI Zhenhua

  Iron and Steel. 2025, 60(11): 134-147. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250253

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  18-roll mills, with their unique roll system configuration and flexible control capabilities, offer significant advantages in producing high-precision, ultra-thin gauge strips. The structural characteristics and rolling mechanism of S6-High type 18-roll mill were analyzed in depth. The position of the 18-roll mill's roll system was systematically studied, and the deflection equations of each roll in different directions were constructed based on the influence coefficient method, especially considering the three-dimensional bending deformation characteristics caused by the side support structure. Subsequently, a physical model for strip shape prediction was established by coupling the metal deformation model, roll system deformation coordination equations, and exit thickness equation, supplemented by force and moment balance equations, to reflect their complex interactions. The model could simultaneously solve the thickness distribution of strip outlet, rolling force distribution, pressure distribution between rolls and transverse distribution of front tension, so as to realize the prediction of strip shape. Furthermore, in view of the small diameter of the working roll of the 18-roll mill, the exponential smoothing method was used to correct the inter-roll force in the iterative process, which effectively ensured the convergence of the model. In addition, combined with a large number of field production data, the particle swarm optimization algorithm was used to optimize the input parameters of the model, which further improved the prediction accuracy of the model. Finally, the production data of S6-high type 18-roll mill in a cold rolling mill were used to verify the prediction performance before and after the optimization of the input parameter coefficient. It is found that the average shape prediction error of the optimized model for all steel grades is reduced by 6.3 I（the shape of the strip is expressed in I units）, and the average prediction accuracy is increased by 8.0%, which proves the necessity of coefficient optimization. The optimized model exhibits an average strip shape prediction error of no more than 1.5 I and an average prediction accuracy of 96.5% on the test set, indicating that the strip shape prediction model for the cold rolling 18-roll mill established possesses high prediction accuracy and fully meets the requirements of practical engineering applications.
Materials
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  Microstructure and properties of 2 400 MPa-grade ultra-high strength steel powder and SLMed alloy

  WANG Shuai, WANG Changjun, GUO Chunhuan, JIANG Fengchun, LIU Zaixi, XU Shuai, BI Zhongnan4, YANG Li

  Iron and Steel. 2025, 60(11): 148-160. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250409

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  The trend towards increasingly thinner and lighter foldable smartphones imposes higher demands on the strength of materials for precision hinge components in the 3C sector. However, the current metal injection molding（MIM）process struggles to simultaneously achieve the required ultra-high strength and good plasticity for hinge parts. A selective laser melting（SLM）additive manufacturing technique was employed to fabricate 2 400 MPa-grade ultra-high strength steel（UHSS）, utilizing powder prepared by vacuum induction melting gas atomization（VIGA）and plasma rotating electrode process（PREP）. Respectively, the characteristics of VIGA and PREP UHSS powders, along with the microstructure and mechanical properties of the SLM-fabricated alloy, were comparatively investigated using SEM, EBSD, and XRD. The experimental results reveal both VIGA and PREP UHSS powders primarily exhibit columnar and cellular grain microstructures. PREP powder, however, demonstrates lower gas/impurity content, superior apparent density, and better flowability. The extremely high cooling rate of PREP induces a distinct crystallographic texture and less FCC phase. The dislocation density in both as-built（AB）and heat-treated（HT）VIGA samples is higher compared to PREP. Nevertheless, significant oxide inclusions exists in SLM VIGA parts due to higher oxygen content, leading to poor plasticity. After solution and aging treatment, PREP-HT samples exhibits significant grain refinement versus VIGA-HT, enhancing the strength-plasticity synergy and achieving a favorable combination of tensile strength（2 406 MPa）and elongation（4.3%）. This research validates the significant advantages of PREP powder in SLM processing of UHSS, offering a new technical pathway to overcome the "high-strength-complex-lightweight" co-design bottleneck for precision components in the 3C sector.
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  Effect of rare earth additions on microstructure and low temperature toughness of freeze-thaw resistant steel

  YANG Bangmin, ZHAO Tianliang, HOU Tingping, LI Yan, CUI Zhongyu, WU Kaiming

  Iron and Steel. 2025, 60(11): 161-174. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250370

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  Rare earths （RE） can purify molten steel, modify inclusions, and refine grains. They have great potential for improving the strength, low-temperature toughness, and corrosion resistance of low-alloy steels. Based on rare earth microalloying, freeze-thaw-resistant low-alloy steel suitable for plateau permafrost, polar regions and other environments can be developed. The effects of different rare earth mass fractions （0.000 4%, 0.005 3%, and 0.012 3%） on the microstructural evolution, tensile properties, and low-temperature toughness of freeze-thaw resistant steel were investigated through optical microscopy, scanning electron microscopy, tensile testing, and low-temperature impact testing, thereby elucidating the mechanism of rare earths in freeze-thaw resistant steel. The results show that the addition of La-Ce mixed rare earth transforms large irregular inclusions in the steel into fine MnS + （La,Ce,AI,Ti）_x（O,N）_y composite inclusions. When the RE mass fraction exceeds 0.005 3%, granular bainite （GB） begins to form in the freeze-thaw resistant steel. Concurrently, the average grain size decreases from 4.22 μm to 2.18 μm, and the average dislocation density increases from 2.66×10¹⁴/m² to 6.63×10¹⁴/m². The modification of RE on inclusions and its effect on microstructural evolution improved the impact and tensile properties of steel. When the RE mass fraction is 0.005 3% the freeze-thaw resistant steel shows the best overall mechanical properties, with its yield strength and tensile strength reaching 444.62 and 565.44 MPa, respectively, while the room temperature and -80 ℃ impact work increase by 44% and 86%, respectively. Compared with that of the unadded rare earths, the onset of the ductile-brittle transition temperature is reduced from -20 ℃ to -80 ℃. The research results demonstrates the positive role of rare earths in the organization and properties of freeze-thaw resistant steels and provides a theoretical basis for the development of rare earth freeze-thaw resistant steels.
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  In-situ high-energy X-ray diffraction analysis of deformation behavior of medium-Mn steel

  ZHANG Minghe, ZHANG Boao, JI Ze, LI Tao, WANG Shuhuan, FENG Yunli

  Iron and Steel. 2025, 60(11): 175-187. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250315

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  Medium-Mn steel has an excellent strength-plasticity match and can achieve automotive lightweighting. It is the most promising third-generation advanced automotive steel. In order to deeply explore the influence of the microstructure and deformation temperature of medium-Mn steel on its mechanical properties, the Fe-0.12C-10.16Mn-1.87Al steel annealed at 650 ℃ for 1 h and 4 h was taken as the research object. The influence of deformation temperature （25 ℃ and -15 ℃） on the micromechanical behavior during the deformation process of medium-Mn steel was studied by in-situ synchrotron-based high-energy X-ray diffraction （HE-XRD） technology. The results show that with the extension of annealing time and the decrease of deformation temperature, the stability of austenite decreases and its rate of transformation to martensite during the deformation process accelerates. The contribution degrees of the relative flow stress of each phase were calculated by using the mixing law. Under different annealing times and deformation temperatures, austenite and ferrite were the main load bearers in the early stage of deformation, while the contribution of martensite to flow stress increased in the later stage of deformation. The work hardening rate of the specimen was decomposed into four components, the change rate of corresponding stress of austenite, the load partitioning between austenite and martensite, the formation rate of martensite, and the load partitioning between austenite and ferrite. The results show that with the extension of annealing time and the decrease of deformation temperature, the contribution of martensite formation rate related to the TRIP（transformation-induced plasticity） effect and the load partitioning between austenite and martensite increase, while the contribution proportion of the phase stress change rate of austenite decreases. Through quantitative evaluation and superposition analysis of each component, the calculated work hardening rate is basically consistent with the trend of work hardening rate determined experimentally. Theoretical and technical support for an in-depth understanding of the composition corresponding load partitioning mechanism related to the TRIP effect in medium-Mn steel can be provided.
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  Effect of cross-section microstructure and variant selection on low temperature impact toughness of thick plate after welding

  QIN Hao, ZHANG Liqin, HU Lei, ZHAN Zilong, WANG Xikai

  Iron and Steel. 2025, 60(11): 188-200. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250306

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  During thick plate welding, significant differences in cooling rates and elemental distribution across different thickness sections result in varied microstructural characteristics within the coarse-grained heat-affected zone （CGHAZ）. The microstructural evolution and low-temperature impact toughness （-60 ℃） of CGHAZ are investigated. The CGHAZ is analyzed at the 1/4-thickness and 1/2-thickness positions within an 80 mm-thick joint made of EH690 high-strength steel. This joint was produced by submerged arc welding （SAW）. Using OM（optical microscope）, SEM（scanning electron microscope）, EBSD（electron back scattering diffraction）, and TEM（transmission electron microscope） techniques, the influence of cooling rate, elemental segregation, and welding thermal cycles on microstructure morphology was systematically analyzed. Results show that the 1/4-thickness position, with a higher cooling rate, forms fine lath bainite （LB） and predominantly island-like M/A constituents, exhibiting a higher high-angle grain boundary （HAGB） line density [（1.53±0.13） μm²] and superior impact energy （220 J）. In contrast, the 1/2-thickness position, due to slower heat dissipation and elemental enrichment from multi-pass welding cycles, develops coarse LB and more fine acicular M/A constituents, with a lower HAGB line density [（1.18±0.12） μm²]; additionally, stress concentration caused by fine recrystallized grains near prior austenite grain boundaries reduces impact energy to 160 J. EBSD characterization revealed that the block unit fraction and variant pairing are critical factors determining toughness differences, with a higher block fraction and a predominance of variant pairs（ V1/V2） observed at the 1/4-thickness position. The mechanisms of microstructure evolution and variant selection in CGHAZ at different thicknesses are clarified by this study, providing theoretical guidance for optimizing thick plate welding processes. The mechanisms of microstructure evolution and variant selection in the CGHAZ at different thicknesses are clarified, providing theoretical guidance for optimizing thick plate welding processes.
Metallurgical Process Engineering
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  Application and practice of intelligent operation control technology in steel manufacturing processes

  GUO Liang, ZHENG Zhong, LIU Xueying, YANG Yongjie, YANG Zhipeng, ZHANG Shiyu, WANG Yongzhou, WANG Ying

  Iron and Steel. 2025, 60(11): 201-214. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250296

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  Steel enterprises face pressing challenges, including overcapacity, significant market fluctuations, weak profitability, imbalanced capacity structures, and high consumption of resources and energy. The adoption of intelligent means to optimize production operation and control is of critical importance for achieving cost reduction, efficiency improvement, and sustainable development characterized by energy conservation and low-carbon emissions. The regulation of steel production relies on the "program" optimization within production planning and scheduling technology to ensure the dynamic order, collaborative continuity, and operational optimization of material flow. Through a study conducted at Jingtang Steel Company, focusing on intelligent control technology for optimizing the steel manufacturing process with production planning and scheduling at its core, an intelligent management and optimization method is proposed. This method centers on rapid order fulfillment and follows the framework of "customer order-production order-planning and scheduling-production scheduling". Tailored to the equipment layout and product manufacturing characteristics of Jingtang Company, the study analyzes the technical features of operational optimization related to manufacturing process optimization control and production planning and scheduling. It introduces a multi-process production batch planning coordination method for medium and heavy plate production lines, encompassing inventory digestion, production order conversion processing, furnace and casting group planning based on slabs, and rolling period planning. The study establishes models for steelmaking-continuous casting-hot rolling operation planning, alongside steel plant production scheduling and dynamic scheduling models, forming a multi-level and multi-process collaborative optimization technology oriented toward order delivery. Engineering application practices of intelligent control technology in the production process of medium and heavy plate production lines demonstrate that this technology enables intelligent control across the entire process of production operation optimization, achieving unified command and multi-process coordination. The operational efficiency of the model is 10.65 times higher than that of the manual experience-based decision-making assisted by the information system. This significantly improves the production efficiency and economic benefits of the entire process, highlighting the technological advantages of the intelligent transformation and upgrading of steel enterprises.
Environmental Protection and Energy
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  Effect of temperature on process mineralogy of titanium-containing blast furnace slag

  LIU Lina, FANG Jun, LIU Xiangshuo, DING Jiacheng, LIU Lei, LIU Jianwei

  Iron and Steel. 2025, 60(11): 215-222. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250287

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  Titanium-containing blast furnace slag contains a significant amount of titanium, but its dispersed distribution across various minerals poses challenges for comprehensive utilization. To investigate the enrichment of titanium and the crystallization behavior of titanium-bearing minerals in titanium-containing blast furnace slag, it employed process mineralogy theory and utilized testing methods such as a transmitted/reflected polarizing microscope, X-ray diffractometer, and electron probe to conduct quantitative analyses of the microstructure, mineral composition, and perovskite grain size of titanium-containing blast furnace slag under different temperature conditions, and systematically studied the occurrence state and migration patterns of titanium. The results indicate that the basic phase composition of titanium-containing blast furnace slag consists of perovskite, primary spinel, secondary spinel, pyroxene, and glassy material. The crystallization temperature of perovskite and primary spinel is above 1 350 ℃, while that of pyroxene is between 1 250 ℃ and 1 300 ℃. As the temperature decreases from 1 350 ℃ to 1 100 ℃, the mass fraction of perovskite first increases and then decreases, and its grain size first coarsens and then refines. At 1 300 ℃, the perovskite mass fraction reaches a maximum of 45.55%, and the mass fraction of particles larger than 20 μm reaches 41.91%. The pyroxene content increases significantly, while the spinel content decreases slightly. The microstructure of high-titanium blast furnace slag is spotted structure, and the perovskite grain size becomes more uniform as the temperature decreases, with no significant change in morphology, primarily exhibiting needle-like and dendritic aggregates. Titanium elements are primarily present in perovskite and secondary spinel, followed by distribution in glassy material, pyroxene, and primary spinel. Titanium elements in the slag migrate from perovskite to other minerals as temperature decreases. Comprehensive analysis indicates that 1 300 ℃ is the optimal temperature for perovskite enrichment and coarsening, providing a theoretical basis for the efficient extraction of titanium from titanium-containing blast furnace slag.
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  Crushing and heat exchange mechanism of blast furnace slag under coupling effect of centrifugal force and air

  ZHEN Changliang, GAO Guangyu, CHENG Cuihua, ZHAO Kai, WAN Xinyu

  Iron and Steel. 2025, 60(11): 223-233. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250307

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  The traditional water quenching process for blast furnace slag suffers from issues such as water resource waste, environmental pollution, and low efficiency in heat recovery, which cannot meet the demands of modern industry for green and efficient development. Against this backdrop, the dry granulation technology of blast furnace slag, with its advantages in environmental friendliness and high heat recovery efficiency, has become a hot direction for upgrading the blast furnace slag treatment technology. A three-dimensional dynamic numerical simulation of the blast furnace slag granulation process and heat recovery was conducted using the fluid dynamics software Fluent, based on the centrifugal force and air coupling granulation mode. It visually presents the continuous evolution process of the blast furnace slag from spreading to stretching, breaking, and granulation under the combined action of centrifugal force and cooling air. Under different key parameters such as the turntable speed and air velocity, the characteristics of the particle size distribution of the granulated blast furnace slag and the system heat exchange efficiency were analyzed to reveal the internal mechanism and heat transfer laws of the dry granulation process of blast furnace slag. The research results show that the turntable speed has a significant impact on the granulation effect. When the turntable speed increases from 2 000 r/min to 4 000 r/min, the average particle size of the granulated blast furnace slag decreases from 3.20 mm to 2.55 mm. On this basis, with the turntable speed fixed at 4 000 r/min, when the tangential air velocity increases from 100 m/s to 500 m/s, the average particle size of the granulated blast furnace slag further decreases from 2.83 mm to 2.39 mm. When the inlet air velocity increases from 100 m/s to 500 m/s, the air outlet temperature rises from 357 K to 986 K, and the increase in air velocity significantly enhances the heat exchange process. When the inlet air velocity is 500 m/s, the theoretical heat exchange efficiency can reach up to 73.12%. Notably, in the above dry granulation process of blast furnace slag, when the turntable speed is 4 000 r/min and the tangential air velocity is less than 200 m/s, the average particle size of the granulated blast furnace slag is slightly larger than that without tangential air loading, indicating that the tangential air has a negative impact on the granulation of blast furnace slag at this time.
Equipment Technology
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  Effects of AGD beams′ arrangement on abrasive wear of screw blades in a COREX furnace

  JIA Shuya, RONG Wenjie, QI Fengsheng, LI Baokuan

  Iron and Steel. 2025, 60(11): 234-245. https://doi.org/10.13228/j.boyuan.issn0449-749x.20250377

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  The COREX process is currently a relatively mature technology for industrial use in non-blast furnace ironmaking processes. The areal gas distribution （AGD） beams are important components in the COREX shaft furnace that ensure the uniform distribution of reducing gas and regulate the flow direction and velocity of the gas. However, the existence of AGD beams will change the movement characteristics of materials in the furnace, thereby affecting the wear behavior of the screw discharger. Therefore, this research project focuses on studying the effect of different AGD beams' arrangement on the abrasive wear of screw blades in a COREX shaft furnace, based on the discrete element method （DEM）, combined with the Hertz-Mindlin non-slip contact model and the Archard Wear model, it systematically explores the distribution characteristics of particle velocity, pressure on the screw blades and wear amount during the discharge process under different arrangements of AGD beams . The results show that, in the shaft furnace without AGD beams, the overall descending process of particles is relatively stable. In the shaft furnaces equipped with AGD beams, the particles above the beams exhibit a lag in their descent, whereas the burden particles surrounding the beams show an advancement in their falling process. In the shaft furnace without AGD beams, the wear distribution among different blades is relatively uniform; in the shaft furnace with AGD beams, the wear amount of the screw blades directly below the AGD beams is smaller. Compared with other arrangements, the overall wear amount of the screw blades in the shaft furnace with four AGD beams is smaller. The pressure and the abrasive wear on the screw blades are both concentrated on the inner and outer edges of the blades. The wear firstly appears in the middle section of each blade, and the wear amount in this section is relatively large. Based on the research findings, in practical production, priority should be given to the cross-arrangement mode of four AGD beams. Secondly, it is recommended that wear-resistant materials should be used in the areas of the blades prone to wear.