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15 March 2025, Volume 60 Issue 3
    

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    Technical Reviews
  • AN Shengli, HUANG Lan, CHAI Yifan, CHEN Yuxin, PENG Jun, ZHANG Fang
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    The iron and steel industry occupies a crucial position in the process of economic and social development. With the continuous growth of China's iron and steel production, the subsequent treatment problem of steel slag has become increasingly prominent. Due to the problems of poor stability, high abrasion resistance and low cementation of steel slag, the treatment and resource utilization of steel slag are restricted, and a large amount of steel slag is piled up for treatment, which not only occupies land resources, but also harms the surrounding environment and residents' lives. In the context of "green sustainable development" and "carbon neutral", in order to meet the urgent needs of modern steel mills for environmental protection and resource reuse, the development of steel slag treatment and resource utilization technology is imperative. It reviews the research progress of steel slag treatment technologies and resource utilization, and introduces the current mainstream treatment technology of steel slag, including pretreatment process, steel slag modification process and wet treatment process. The technical characteristics of different treatment processes, resource recovery and potential application pathways of products are elaborated in detail, and the technical advantages of different treatment processes are analyzed. In addition, the exploration and research progress of steel slag in the field of environmental remediation are discussed and analyzed, pointing out the application potential of steel slag in this field and the future research direction. The resource utilization of steel slag in China is still facing many problems such as pre-treatment and technological breakthroughs for the expansion of high-quality application areas. The purpose is to analyze the overview of steel slag treatment technology and resource utilization, and to propose that the future research on steel slag, while focusing on the full use of sensible heat and the recovery of valuable resources such as iron, should focus on and strengthen the basic research on the regulation of the evolution of steel slag composition and physical phase. On this basis, new technologies should be developed in the direction of environmental remediation, preparation of new materials and high-value products to expand the high-quality utilization of steel slag and improve the comprehensive utilization rate of steel slag.
  • ZHUANG hangling, XIANG Jianghua
    Iron and Steel. 2025, 60(3): 13-25. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240518
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    Differential scanning calorimetry (DSC) is a precise technique for quantitatively analyzing thermophysical changes and thermal transition information in materials during thermal variations, characterized by high accuracy, rapid testing, and minimal sample requirements. The advancements in DSC have significantly broadened the scope of material property testing in steel and alloy research, facilitating a deeper investigation into the thermodynamics and kinetics of material thermal transitions. It commences with the fundamental theory of DSC, detailing its classifications and signal compositions, and offers a comprehensive overview of DSC's current applications in steel and alloy research. The advantages and limitations of DSC, particularly in the study of specific heat, phase transitions, precipitation and decomposition of secondary phases, and the glass transition in amorphous alloys are discussed. The integration of DSC with other techniques is also explored. Furthermore, it summarizes the current state of kinetic research utilizing thermal analysis data from DSC, including studies on activation energy and transition mechanisms in alloy phase transitions, as well as the development of kinetic models for alloy transformations. A comprehensive analysis of the thermophysical parameters of steels and alloys through DSC, combined with an in-depth understanding of the thermodynamics and kinetics of alloy phase transitions, is expected to provide robust theoretical support for the development, manufacturing, and application of alloy materials.
  • Raw Material and Ironmaking
  • WANG Xindong, ZHANG Wenqiang, GAO Bing, PAN Jian
    Iron and Steel. 2025, 60(3): 26-35. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240457
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    Compared with sintering production, pellet production is more energy-efficient and environmentally friendly. The burden structure with high proportion of pellet is an effective way for blast furnace to achieve low carbon and green ironmaking. It is the key to realize the industrial production of fluxes pellets in blast furnace for high proportion pellet smelting. The belt roasting machine to produce fluxes pellets has great technological advantages. The three 3 000 m3 blast furnaces in Tangsteel New District designedly adopted 50%-70% pellet structure, and two 624 m2 large-scale belt roasting machines were set up. In order to break the long-term technological monopoly for large-scale belt roasting machine abroad, the comprehensive research and development on the process technology and equipment of belt roasting machine was carried out in Tangsteel. Through the development of fine powder pretreatment, ore blending and roasting technology, the production technology of medium and high silicon flux pellets was mastered. With the design, manufacture and application research for the equipment localization, the localization of the core equipment of the large-scale belt roasting machine was realized to break the long-term monopoly of foreign countries. Through the development and application of intelligent technology, the efficient cooperation of pellet production line was obtained, and the production efficiency of belt roasting machine was significantly improved. Additionally, with the development and application of low energy consumption and low emission technology, the energy consumption and pollutant emission of the pelleting process were significantly reduced, the low-carbon and green production was realized. Apparently, the development and application of large-scale belt roasting machine in Tangsteel has achieved the full independent research, development and design of large-scale belt roasting machine and the localization of equipment for the first time, which has opened up a new situation for the promotion and application of belt roasting machine. To date, the production technology of flume pellets and the smelting technology of high proportion pellet in blast furnace have been mastered by Tangsteel. And these exploration and practice for burden structure in blast furnace of Tangsteel have played the good leading and demonstrative role in the popularization and application of burden structure with high proportion pellet in China.
  • HAN Xiuli, DUAN Bowen, LI Mengqian, SI Tianhang, WANG Weiwei, RAO Mingjun
    Iron and Steel. 2025, 60(3): 36-44. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240540
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    The low-temperature reduction degradation index(IRD>3.15 mm) is a critical measure for assessing the quality of sinters. However, complicated test methods, high equipment requirements, and long test times are the existing problems. The thermoelectric coefficients of five representative high-basicity sinters from Hebei Province were systematically assessed using polarizing microscope and thermoelectric coefficient tester to identify a straightforward, eco-friendly, and effective testing approach. Moreover, the relationship between the thermoelectric properties of these sinters and IRD>3.15 mm was examined. The results show that the 5 typical high-basicity sinters have obvious thermoelectric properties, and the thermoelectric coefficient is mainly distributed in 60-270 μV/℃. Furthermore, a significant negative relationship is observed between the thermoelectric coefficient and IRD>3.15 mm. Due to the heterogeneity of the sinter structure, there is a variation in the thermoelectric characteristics across different sections of the same specimen. The area where the protogenetic granular hematite is concentrated has no thermoelectric property. The thermoelectric coefficient of the interlaced/erosion structure composed of silica-ferrite of calcium and aluminum (SFCA) and magnetite is mainly distributed in the range of 60-160 μV/℃, and the average thermoelectric coefficient is 114.77 μV/℃. The thermoelectric coefficient of the concentrated secondary skeleton crystalline hematite is significantly increased in the region of orientation, mainly distributed in 190-270 μV/℃, and the average thermoelectric coefficient is 221.81 μV/℃. The secondary skeleton crystalline hematite content is the key factor in determining the average value of the pyroelectric coefficient of the sinter. With the increase of the secondary skeleton crystalline hematite content, the average value of the pyroelectric coefficient of the sinter increases, and the IRD>3.15 mm decreases. There are obvious correlations among the sinter's average thermoelectric coefficient, secondary skeleton crystalline hematite content, and the low-temperature reduction disintegration index IRD>3.15 mm. The results provide a new idea for evaluating the low-temperature reduction pulverization properties of sinter and have guiding significance for applying mineral thermoelectric characteristics in the metallurgical field.
  • WU Yaming, HUANG Yun, TAO Linhe, WU Zhikang, CAI Xuebin, ZUO Haibin
    Iron and Steel. 2025, 60(3): 45-55. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240531
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    Reasonable operation of the furnace type is the key to its long life, stable operation, and sound economic and technical indicators for the blast furnace. Based on the production data of a certain steel plant's blast furnace, the blast furnace type optimization method was studied, providing scientific guidance for blast furnace operation. First, the Isolation Forest and Boxplot methods were adopted to identify and process noise in the data, and then Principal Component Analysis (PCA) was used for dimensionality reduction to eliminate noise and data redundancy, providing a high-quality data foundation for subsequent cluster analysis. Next, the application effects of two clustering algorithms, K-means and DBSCAN, were compared. The K-means algorithm achieved the best silhouette coefficient when the number of clusters was 14, indicating that the blast furnace type could be divided into 14 categories; the DBSCAN algorithm exhibited a lower Davies-Bouldin Index(DBI) when Neighborhood Radius (Eps) and Minimum Neighborhood Sample Count(min_samples) were 6.25 and 2, showing the best clustering effect and the ability to effectively identify clusters of any shape, especially suitable for handling the complexity and nonlinearity of blast furnace production data. To evaluate the advantages and disadvantages of different furnace types, an evaluation method for operating furnace types based on comprehensive production indicators was established, selecting coke ratio, fuel ratio, output, and iron loss as key performance indicators and assigning different weights. The results show that the fourth type of furnace type performs the best in terms of blast furnace operation indicators and can be used as the operating target for a reasonable furnace type. To achieve blast furnace type optimization, the implicit relationship between blast furnace operating parameters and furnace types was explored using the Random Forest method, determining the key feature parameters that affect furnace types, including burden matrix parameters, permeability index, gas utilization rate, and standard wind speed. By analyzing the evolution of furnace types and the trend of blast furnace parameters, it is found that the deterioration of furnace types is mainly related to the decrease in permeability, which leads to uneven airflow distribution, reduces gas utilization rate, and increases pressure drop. A new method for optimizing blast furnace type management is established, providing valuable data analysis and operational guidance for on-site personnel, helping to improve blast furnace operation level, reduce energy consumption and costs, and achieve long life, stable operation, and efficient production of blast furnaces.
  • Steelmaking
  • GAO Zhizhe, LÜ Ming, HOU Nana, HAO Yijie, WEI Guoli, HOU Fuqing
    Iron and Steel. 2025, 60(3): 56-65. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240525
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    The smelting tasks at blowing stage in converter vanadium extraction process are different,and the composition and temperature of the molten pool are constantly changing,which makes the working conditions such as oxygen supply lance position and flow rate change at different stages of smelting,resulting in different stirring characteristics of the molten pool at different stages of blowing. The stirring energy model of converter molten pool was established,and the effects of temperature,oxygen supply flow and bottom blowing on the stirring energy of molten pool in different blowing stages were studied. It is found that the energy density of top blowing stirring in each stage of converter vanadium extraction process is significantly smaller than that of bottom blowing stirring,and the CO bubble stirring energy generated by chemical reaction only accounts for 0.41%-1.74%. With the smelting process,the top blowing stirring energy density decreases from 165.30 W/t to 144.63 W/t,and then gradually increases to 192.84 W/t. The stirring energy density produces by CO bubbles is up to 15.21 W/t. The stirring energy density produced by bottom blowing nitrogen gradually increases from 786.92 W/t to 865.57 W/t. In the smelting process,the stirring energy of the molten pool is reasonably increased by changing the top blowing lance position and bottom blowing flow rate at different stages,and the carbon loss can be effectively reduced. On this basis,the effects of different Mach number,oxygen flow rate,lance position and bottom blowing intensity on the impact characteristics and mixing time of molten pool were studied by 1∶3 water model experiment. With the progress of blowing,the impact depth of the molten pool is 61-90 mm under the condition of Mach number of 1.97,and the impact range of the molten pool is 19.93%-29.41%. The change degree of impact diameter is 37.41%-42.54%. The longest mixing time is 54 s and the shortest is 39 s. The process system of vanadium extraction from converter is optimized. In addition,when the bottom blowing intensity is greater than 0.09 m3/(min·t),the mixing time of the molten pool is significantly reduced. When the bottom blowing intensity reaches 0.12 m3/(min·t),the stirring intensity of the molten pool decreases. When the bottom blowing flow rate increases to 0.15 m3/(min·t),the mixing time of the molten pool reaches a minimum of 27 s. In order to reduce the mixing time of the molten pool,the bottom blowing intensity can be appropriately increased to improve the efficiency of vanadium extraction. It is beneficial to achieve vanadium extraction and carbon conservation in the converter by adjusting the lance position and gas supply intensity at different stages of vanadium extraction and blowing,and reasonably controlling the stirring characteristics of the molten pool.
  • SONG Jintao, CHEN Chao, WANG Tianyang, GENG Mengjiao, RONG Zhiren, REN Dekang, WANG Jia, FAN Jinping
    Iron and Steel. 2025, 60(3): 66-77. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240538
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    Two types of turbulence inhibitors, namely cylindrical turbulence inhibitor and impact pad, were used in a 6-strand tundish with side-arranged inlet of a steelmaking plant. In order to evaluate the metallurgical effect of the two types of tundish during the ladle changeover process, the flow field distribution of the two type of tundishes and the slag entrapment situation in the water model, evolution of inclusions during the ladle changeover process were studied by industrial sampling, physical model, and numerical simulation methods. Particle image velocimetry (PIV) was applied to measure the flow field distribution and velocities at the water oil interface. The morphology, size, and composition of inclusions in the two type of tundishes during the ladle changeover process were explored by industrial sampling and Scanning Electron Microscopy-Energy Dispersion Spectrometer (SEM-EDS). The results show that the velocity spatial distribution inside the tundish is uneven, with higher velocity in the impact zone and lower velocity at the edge strand. There is an upward backflow in the tundish with a cylindrical turbulence inhibitor. At a normal casting rate of 2.65 t/min, the maximum fluid velocity at the water oil interface of both types of tundish is around 50 mm/s, indicating a relatively stable water oil interface. When rapidly refilling (5 t/min) after ladle change, a circulation is formed near the wall in the impact zone of the tundish with a cylindrical turbulence inhibitor, and a strong horizontal flow that paralleling to the liquid surface towards the outlet is formed. The maximum velocity at the water oil interface is 285.16 mm/s, and the slag eye area is 735.42 cm². A large number of large-sized oil droplets are entrained in the impact zone. For the tundish with an impact pad, the impact zone forms an upward flow field along the wall, with a maximum velocity of 186.54 mm/s at the water oil interface and a slag eye area of 399.27 cm². Small oil droplets are entrained in the impact zone, forming a water oil mixture. The sampling results before and after the ladle change show that no large-sized (≥50 μm) inclusions are found in both types of tundish at the end of casting of the previous heat. After the liquid level rise to the normal working level, a large-sized inclusion with a size of 240.32 μm is found in the tundish with a cylindrical turbulence inhibitor. The average size of the inclusion increases from 13.18 μm to 29.88 μm, and the proportion of large-sized (≥50 μm) inclusions is 24%. The mass fraction of CaO in the inclusion increases significantly. However, no inclusions with a size larger than 100 μm are found in the tundish with an impact pad, and the average size of inclusions remains basically unchanged. The proportion of large-sized (≥50 μm) inclusions is 6.7%. Overall, the metallurgical effect of the impact pad is superior to that of the cylindrical turbulence inhibitor.
  • CHEN Guojun, LIU Xiaofeng, WANG Jujin, CHEN Lutao, REN Ying, BAO Guangtuan, ZHANG Lifeng
    Iron and Steel. 2025, 60(3): 78-85. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240555
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    To study the effect of w((CaO))/ w((Al2O3)) in the refining slag on the molten steel during the secondary refining process, the w((CaO))/ w((Al2O3)) was adjusted through industrial trial. The change of the sulfur content in steel was analyzed. The results shows that the desulfurization ability of the refining slag with the w((CaO))/ w((Al2O3)) of 2.0 is better than that of refining slag with the w((CaO))/ w((Al2O3)) of 1.6. The melting temperature, solid phase fraction, viscosity, and sulfide capacity of the refining slag with different w((CaO))/ w((Al2O3)) are calculated. When the w((CaO))/ w((Al2O3)) in the refining slag exceeded 1.8, the refining slag transitions from the liquid phase to a semi-liquid phase, and the solid phase fraction of the refining slag increases continuously at 1 873 K. The influence of viscosity kinetic factor on the desulfurization ability of slag was considered. A dimensionless desulfurization index of Sindex was proposed to represent the desulfurization ability of the refining slag. It is revealed that with the increase of w((CaO))/ w((Al2O3)) in the refining slag, the viscosity of the slag first decreases and then increases. When the w((CaO))/ w((Al2O3)) is 1.8, the viscosity η reaches a lowest level. With the increase of w((CaO))/ w((Al2O3)) in the refining slag, the sulfur capacity Cs gradually increases. With the increase of w((CaO))/ w((Al2O3)) in the refining slag, the value of Sindex first increases and then decreases. When the w((CaO))/w((Al2O3))of the slag is 2.0, the value of Sindex reaches a highest level. It is suggested that control the w((CaO))/w((Al2O3)) of the slag within the 1.8 to 2.0 is more beneficial for improving the desulfurization ability of the slag. Finally, the Sindex of CaO-Al2O3-SiO2-5.68%MgO refining slag at 1 600 ℃ was calculated. In the liquid region of the refining slag, the Sindex increases with a higher w((CaO))/ w((Al2O3)) in the refining slag, which is beneficial to improve the desulfurization efficiency of the molten steel.
  • Metal Forming
  • WANG Bo, WU Hongjie, SUN Ligen, XIAO Pencheng, ZHU Liguang, ZHANG Caidong
    Iron and Steel. 2025, 60(3): 86-94. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240496
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    IF steel is widely used in automobile panel and home appliance panel manufacturing due to its excellent deep drawing performance. Therefore, there are strict requirements for its surface quality, and surface quality defects caused by large-size inclusions are still inevitable problems in the production process. According to the size and distribution of large size inclusions in IF steel, the deformation characteristics of large size inclusions in different positions and sizes during rolling process were studied. The laboratory hot rolling experiment was carried out by the method of prefabricating inclusions in the slab, and the corresponding finite element model was established. The correctness of the model was verified by experiments. At the same time, according to the on-site rolling process, a rolling process evolution model of large-scale inclusions in the surface layer of IF steel slab was established. The deformation law of inclusions with diameters of 0.1, 0.5 and 1.0 mm at different depths from the surface was analyzed. It is found that the closer to the surface, the greater the length change of inclusions along the rolling direction. The deformation rates of inclusions with a diameter of 0.1 mm from the surface of 5, 10 and 15 mm are 11.353,9.884 and 7.859, respectively. The deformation rates of inclusions with a diameter of 0.5 mm are 9.124,8.016 and 7.411, respectively. The deformation rates of inclusions with a diameter of 1.0 mm are 7.906,7.156 and 6.830, respectively. By comparing the deformation law of inclusions with different diameters at the same position, it can be found that the larger the diameter of inclusions with the same depth, the smaller the deformation rate. The deformation rates of inclusions with diameters of 0.1, 0.5 and 1.0 mm from the surface layer 5 mm are 11.353,9.124 and 7.906, respectively. The inclusions deformation rates of 10 mm from the surface layer are 9.884,8.016 and 7.156, respectively. The inclusions deformation rates of 15 mm from the surface layer are 7.859,7.411 and 6.830, respectively. At the same time, it is found that the deformation of inclusions is not obvious when the total reduction rate is less than 30% at the initial stage of rolling, and with the increase of the reduction rate for the rolled piece thickness, the inclusions are obviously elongated along the rolling direction.
  • LI Xiaohua, LI Xu, YUAN Hao, HAN Yuejiao, WANG Qinglong, WANG Pengfei
    Iron and Steel. 2025, 60(3): 95-103. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240533
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    In the production of high-quality strip, the phenomenon of performance difference in the wide direction of hot-rolled high-strength strip has a greater negative impact on its quality stability control in the cold rolling process, which is one of the main reasons for restricting the accuracy of strip shape control of this type of product, and also one of the bottlenecks restricting the further thinning of the specifications for this type of the strip. For such problems, taking 1 780 mm strip cold rolling mill as a prototype, a three-dimensional cold rolling simulation model of high-strength strip was established based on the elastic-plastic finite element method, taking into account the differences in the distribution of the wide direction for performance of the rolled strips. The calculated value of thickness distribution in the wide direction and the measured thickness distribution had a high degree of consistency. The relative error between calculated value and measured value of rolling force in the stable rolling stage was controlled with in ±6%, and the relative error between caculated value and measured value of center thickness in wide direction was controlled with ±0.2%. Through the numerical simulation of wide direction performance differentiation, the influence of wide direction performance difference on the three-dimensional deformation of rolled metal, rolling pressure distribution and strip shape regulation were analyzed, and the influence of such differences on the plate convexity and strip shape were described. The results show that the three-dimensional distribution of rolling force between the work rolls and the strip in the contact deformation zone is highly similar to the distribution trend of original mechanical properties of the strips, while the rolling force of the homogeneous model is nearly consistent throughout the strip width range. The inherent differences in the wide direction performance result in an asymmetric influence of the actuators on the adjustment of the crown and flatness. The strip shape control becomes more challenging as the difference in deformation resistance between the center and the edge of the strip increases, and becomes more difficult as the average deformation resistance in the wide direction of the strip increases. Under the same conditioning process, the flatness actuators are less capable of conditioning the shape of strips with primitive differences in wide direction properties than that of homogeneous strips, which ultimately leads to deviations in strip shape conditioning.
  • LUO deng, ZHU Tuo, GAO Hailiang, XIAO Daheng, LI Yanmei, YE Qibin
    Iron and Steel. 2025, 60(3): 104-116. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240482
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    Controlled rolling controls the austenite state, which is essential for the microstructure and properties of direct-quenched high-strength steel. EH500 high-strength steel was focused on to examine how variations in controlled rolling parameters affect its microstructure and mechanical properties following online direct quenching. After controlled rolling at different temperatures, the steel plates were directly quenched starting at 780, 820 and 860 ℃, followed by tempering heat treatment at 550 ℃.Results show that as the direct quenching temperature increases, the microstructure changes from banded to uniform distribution, with the volume fraction of ferrite decreasing from 60% to 20% and bainite increasing from 40% to 80%. The grain size increases from 5.0 µm to 5.4 µm, and the high-angle grain boundary density increases from 0.34 µm-¹ to 0.41 µm-¹. The texture components evolve from deformation textures {113}〈110〉 and {332}〈113〉 to rotated cube texture, with the texture intensity significantly decreasing from 8.92 to 3.26 and 2.64. Tempering has a weak effect on the microstructure morphology, ferrite-to-bainite ratio, grain size, and texture component types, but it transforms martensite/austenite constituents into carbides, increases the high-angle grain boundary density to 0.37-0.42 µm-¹, and reduces the texture intensity to 3.88, 2.71, and 1.82. Increasing the direct quenching temperature can raise the yield strength from 438,509 and 529 MPa, but lower the impact energy at -40 ℃ from 87 J to 84 J and 56 J. After tempering at 550 ℃, the yield strength increases to 526, 556 and 560 MPa, while the impact energy at -40 ℃ improves to 237, 266 and 256 J, respectively, all meeting the strength and impact toughness requirements for EH500 steel.
  • Materials
  • LIU Man, ZHOU Mingxing, CHEN Zhenye, YIN Weifan, XU Guang
    Iron and Steel. 2025, 60(3): 117-124. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240552
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    At present, the classical K-M(Koistinen-Marburger) model is commonly used to describe the martensite transformation kinetics in steel, but the accuracy of the model is closely related to the composition of the steel. Based on quenching experiments with different cooling rates, the martensite transformation kinetics of common medium-carbon high-silicon quenching-partitioning(Q&P) steels were studied by expansion method and metallography method. Meanwhile, an improved martensite transformation kinetic model suitable for medium-carbon high-silicon Q&P steels was established based on the traditional K-M model and verified. The results show that under different cooling rates, the martensite transformation kinetic curves of medium-carbon high-silicon Q&P steel are "S" shape, not "C" type. The phase transformation process is divided into the acceleration period at the beginning, the high-speed period in the middle, and the deceleration period in the end, which may be caused by the self-tempering phenomenon of martensite. In addition, the martensite formed near the martensite start temperature is relatively coarse, and carbon atoms diffuse from the supersaturated martensite to the surrounding unconverted austenite at the relative high temperature. The carbon enrichment of austenite increases the stability of remaining austenite, and the supercooling degree for the further martensite transformation needs to be further increased, thus reducing the martensite start temperature of the remaining austenite. The equation of martensite transformation kinetics index β is a constant of 1-2. The sensitivity of β value to quenching temperature depends on the carbon content of steel. When the carbon content increases, the sensitivity of β value to quenching temperature decreases significantly and can be basically ignored. The rate parameter α is a cubic polynomial function of the quenching temperature. With the increase of cooling rate, the rate parameter α gradually decreases, indicating that the martensitic transformation may be a time-dependent phase transformation. The equation index β gradually increases with cooling rate, which is related to the suppression of austenite plastic accommodation on martensite transformation. Considering the instantaneous dynamics of martensite transformation, the improved K-M model has a better match with the experimental data than the traditional K-M model.
  • WANG Wei, KE Deqing, LI Hang, PAN Yingjun, YANG Wenbin
    Iron and Steel. 2025, 60(3): 125-137. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240423
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    The regulation of carbides in cold work die steel remains a critical concern in the industry. In order to improve the performance of domestic die steel and extend its service life, carbonitrides in Cr8 cold work die steel in domestically produced electroslag remelting state was investigated. Comprehensive analysis of the precipitated phases of the test steels was performed by using scanning electron microscopy (SEM), electron probe microscopy (EPMA), and high-resolution transmission electron microscopy (HRTEM) and etc. The phase diagrams of the test steel under equilibrium solidification conditions were calculated using the Thermo-Calc-TCFE7 database. Based on the Wagner and Scheil model, solubility product of carbonitrides at different temperature intervals and precipitation temperature of carbonitrides from test steels under non-equilibrium solidification conditions were calculated. The results reveal that the precipitates of electroslag remelting state of Cr8 cold work die steel contain M7C3(M=Cr,Fe), MC(M=V), M2C(M=Mo), M23C6(M=Cr, Fe), M6C(M=Mo, Fe), TiN-VC type carbonitrides. Among these, TiN is first precipitated in the liquid phase and is the nucleation core of the precipitated carbides. The eutectic carbide Cr7C3, VC and Mo2C precipitates along the grain boundary in the liquid phase at 1 618, 1 560, 1 528 K at the solid-liquid front, and the size is greater than 5 μm. The secondary carbide Cr23C6 inside the grain is finally precipitated in the solid phase at 1 083 K, which is nano-scale carbide with a size less than 500 nm. In addition, the coarser sizes of eutectic carbides Cr7C3, VC, and Mo2C precipitated in the solid-liquid two-phase region at grain boundaries is attributed to the rate of carbide growth is greater than the rate of nucleation influenced by the supercooling of the solid-liquid front. Therefore, increasing the solidification rate, nucleation rate and forging and heat treatment temperature is an effective way to control the size of eutectic carbides in steel. Promoting the uniform precipitation of secondary carbides M23C6 and M6C can improve the comprehensive mechanical properties of Cr8 cold work die steel. The study result provides an effective theoretical basis for the improvement of the heat treatment process and the control of the second phase of Cr8 cold work die steel.
  • LIU Jilong, WANG Heng, ZHOU Lixin, WAN Wuxia, GAO Jifeng, XU Gaoyong, SUO Jinping
    Iron and Steel. 2025, 60(3): 138-146. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240476
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    Introducing irreversible hydrogen trap into steel is a common method to improve the hydrogen embrittance resistance of structural steel. In order to reveal the hydrogen trap characteristics of TiN precipitated phase interface in high strength steel based on α-Fe matrix, based on the microscopic analysis of TiN/α-Fe interface, the hydrogen trap properties of 0.21Ti-0.08N-Fe (mass fraction,%) materials with different TiN/α-Fe interface misfit were characterized by thermal desorption spectroscopy, and the hydrogen adsorption strength of the hydrogen trap at the TiN/α-Fe interface was simulated by first principles simulation calculations to explore the mechanism of hydrogen adsorption at the hydrogen traps on the interface. The results show that the characteristics of desorption peaks at low temperature are very similar in the four samples with different TiN/α-Fe interfaces. The peak at middle temperature is positively correlated with the content of semi-coherent interface in the sample, and the peak at high temperature is positively correlated with the content of TiN/α-Fe interface in the sample. The sample with the most coherent TiN/α-Fe interfaces has the most irreversible traps, and the binding ability of different interfaces to hydrogen atoms is in the order of coherent interface>semi-coherent interface>non-coherent interface. The simulation calculation results show that the octahedral gap, mixed tetrahedral gap and pure iron tetrahedral gap are all effective binding sites for hydrogen atoms on the coherent TiN/α-Fe interface with B-N orientation relationship, and the octahedral gap has the lowest hydrogen binding energy (-0.10 eV). The hydrogen binding energy of the mixed tetrahedral gap closer to the interface (-0.04 eV) is lower than that of the pure iron tetrahedral gap (-0.01 eV). The variation of atomic spacing and charge density distribution around the interstitial gap before and after hydrogen atoms are dissolved shows that the stress field generated by lattice mismatch at the α-Fe side of the interface can promote the binding of the three interstitial gaps, especially the octahedral gap, to the hydrogen atoms, which can effectively hinder the diffusion of hydrogen in the steel. The properties of TiN/α-Fe interface in steel can be controlled by proper heat treatment, the content of irreversible hydrogen trap can be increased, and the hydrogen diffusion coefficient can be reduced, which is beneficial to improve the hydrogen embrittance resistance of microalloyed structural steel.
  • ZHANG Kaixin, XIAO Guizhi, WANG Fan, ZOU Yutianqi, ZOU Dening, ZHANG Wei
    Iron and Steel. 2025, 60(3): 147-155. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240520
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    Concentrated solar power plants usually use a mixture of NaNO3 and KNO3 molten salt as the heat transfer fluid for the thermal storage system. The high-temperature corrosion resistance of 304 austenitic stainless steel used for the thermal storage system structure in the molten salt environment is particularly important. The influence of microalloying element Nb on the steel mainly lies in the refinement of grains, precipitation strengthening, and improvement of toughness. However, the mechanism of 304 austenitic stainless steel's high-temperature corrosion in molten salt under Nb is not clear, which is worth further research. Two groups of test steels containing 0.49Nb and 0Nb were subjected to a 0-200 h molten salt corrosion test at 565 ℃ under a constant temperature molten salt immersion method, and the corrosion mass loss was measured and the corrosion rate was calculated. The corrosion layer and base material organization were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). The research results show that when the corrosion time is 200 h, the corrosion rates of 0Nb and 0.49Nb are 178.1 μm/a and 133.9 μm/a, respectively, indicating that adding Nb element can improve the resistance to molten salt corrosion. Both samples form a double corrosion product layer on the surface, with the inner layer mainly being FeCr2O4 and the outer layer being Fe2O3 and Fe3O4. The internal stress generated by Fe oxides is easy to produce defects or cause the corrosion layer to peel off, leading to the intrusion of oxidizing ions in the molten salt and the deterioration of the protective properties of the Fe oxide layer. Nb has a low content in the corrosion layer and forms uniform and dispersed NbC in the steel matrix, inhibiting the precipitation of Cr carbide at grain boundaries, while the precipitation of Cr carbide at grain boundaries is prone to causing intergranular corrosion, and intergranular corrosion will introduce more stress into the corrosion layer. The corrosion layer of the steel sample without Nb is thicker and has more cracks, indicating that the addition of Nb element can improve the high-temperature corrosion resistance of 304 austenitic stainless steel in molten salt.
  • Environmental Protection and Energy
  • WANG Yifan, YU Qinghai, LI Yafei, LUO Yunfei, DING Long, LI Yongtao, LONG Hongming
    Iron and Steel. 2025, 60(3): 156-165. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240527
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    The iron ore sintering process primarily depends on coke and coal for energy, leading to significant emissions of volatile organic compounds (VOCs) in the sintering flue gas. These emissions pose risks to both the atmospheric environment and human health. Current research has mainly focused on the total emissions and composition of VOCs in sintering flue gas, but there is limited research on the emission characteristics of VOCs during the sintering process. Utilizing sintering pot experiments and VOC emissions from the windbox ducts of a sintering machine, the characteristics of VOC emissions during the sintering process were investigated. It explored the impact of pulverized coal and coke on VOC emission patterns and assessed the effect of fuel structures on VOC emissions. The findings show that VOCs are emitted continuously throughout the sintering process, with emission concentrations ranging from 100 to 200 mg/m3, attributable to variations in process parameters among different sintering machines. Non-methane hydrocarbons (NMHCs) constitute approximately 10% of the total VOC mass concentration. The release of VOCs in the sintering process can be categorized into four stages. In stage I, VOC levels are relatively high, primarily due to the incomplete combustion of ignition gas. In stage II, VOC emission concentrations increase slightly but remain relatively stable. In stage III. as the over-wet zone in the sinter bed disappears, VOC levels decrease significantly, and NMHCs absorbed in the over-wet zone are released in high concentrations. In stage IV, the sintering cycle concludes, and VOC levels approach zero. When using coke as fuel, the total VOC and NMHC concentrations in the sintering flue gas are significantly lower compared to pulverized coal. However, the proportion of NMHCs within the total VOC emissions is higher when coke is used. The primary components of NMHCs include toluene, ethyl lactate, benzene, acetone, and n-pentane, with aromatic compounds being the dominant constituents. It specifically examines the emission concentrations and trends of VOCs, total volatile organic compounds (TVOCs), and NMHCs during the four stages of the sinter production process. It identifies the primary sources of VOCs in iron ore sintering and offers guidance for reducing VOC emissions in sinter production facilities.
  • WANG Lin, LUO Guoping, HAO Shuai, AN Shengli, CHAI Yifan, ZHANG Zhiming, LI Xiaoli
    Iron and Steel. 2025, 60(3): 166-177. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240477
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    In order to realize the efficient treatment and resource utilization of steel slag, it aims to use blast furnace slag as a "modifier" to modify high basicity steel slag,improve the physical properties of steel slag, optimize the mineral composition of steel slag,and reveal the influence mechanism of slag microstructure on viscosity. The experimental raw materials and modified slag were analyzed by high temperature physical property tester,X-ray diffractometer(XRD),scanning electron microscope(SEM-EDS)and Raman spectroscopy(Raman). The results show that with the increase of the basicity(1.6-2.4)of the mixed slag,the melting temperature decreases first and then increases. When the basicity is 2.0,the high-temperature physical properties are the best. At this time,the proportion of blast furnace slag is 35.19%(mass fraction),the melting temperature is 1 383.30 ℃,the melting time is 1.05 s,and the viscosity(temperature more than 1 405 ℃) is lower than 0.25 Pa·s.The homogeneous reaction effect is good,and the structure of each mineral is clear and evenly distributed. It is mainly composed of gehlenite(Ca2Al2SiO7),magnesium pyroxene(Ca3MgSi2O8), cementitious minerals dicalcium silicate(Ca2SiO4)and tricalcium aluminate(Ca3Al2O6),which realizes calcium stabilization and enrichment of cementitious materials. In addition,with the increase of basicity from 1.6 to 2.0,the high polymerization degree units in the slag microstructure undergoes a depolymerization reaction,and the relative content of the low polymerization degree unit QSi0 increases,which simplifies the microstructure and reduces the polymerization degree parameter n(BO/T)e(the average number of bridging oxygen per tetrahedron in the network structure)to a minimum value of 0.87.When the basicity increases from 2.0 to 2.4,the role of [AlO4] in network construction is enhanced,the number of high polymerization degree units QAl3 and QAl4 increases,and the n(BO/T)e value increases to 1.69. The calculated value of n(BO/T)e is in good agreement with the experimental results of viscosity. This study can provide reference for the research on the viscosity of blast furnace slag quenched and tempered steel slag,the optimization of the phase composition and structure of steel slag,and is expected to promote the resource utilization of iron and steel solid waste(blast furnace slag,steel slag).
  • ZHANG Lu, ZHOU Xianlin, LUO Yanhong, WAN Junying, LI Liuying, CHEN Tiejun, JIANG Jiaying, YU Zhengxiong
    Iron and Steel. 2025, 60(3): 178-186. https://doi.org/10.13228/j.boyuan.issn0449-749x.20240536
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    Steel slag tailings are the main solid waste produced in the steelmaking process. With the increase of steel production, the stock of steel slag tailings is increasing year by year, which has a great impact on the environment. The content of basic oxides such as CaO in steel slag tailings is high. One of the most important ways to use it is to replace part of the sintering flux to return to sintering, but it cannot be determined whether the steel slag tailings participate in sintering and mineralization. The influence mechanism of steel slag tailings on sintering and mineralization is unknown. Therefore, with the help of the basic characteristics test method of high temperature sintering, the influence of using steel slag tailings and Ca(OH)2 reagent to adjust the basicity on the basic characteristics of high temperature sintering was studied, and the sintering cup experiment to verify whether the steel slag tailings were involved in the sintering reaction was carried out. The process mineralogy analysis of sinter was carried out by X-ray diffraction and metallographic microscope, and the related mechanism of steel slag tailings participating in mineralization was revealed. The results show that the assimilation temperature of the sintering raw material with steel slag tailings decreases and the liquid phase fluidity index increases. The main factor is that the steel slag tailings contain SiO2. When the content of SiO2 increases, the low melting point compounds of olivineincrease correspondingly, which will promote the formation of silicate low melting point system, so as to increase the amount of liquid phase and enhance the strength of the bonding phase. At the same time, the Al2O3 in the steel slag tailings will promote the formation of composite calcium ferrite, which is conducive to obtaining the best bonding phase, and the amount of calcium ferrite increases significantly. When steel slag tailings are used as flux, under the condition of basicity 1.82, the drum strength of sinter reaches 65.5%, and the yield reaches 82.8%. In the microstructure of sinter, hematite and magnetite are mostly porphyritic structure, and calcium ferrite is mostly acicular. The dicalcium silicate is mostly willow leaf-like, and the calcium ferrite and magnetite are interwoven and embedded in the structure, indicating that the addition of steel slag tailings in sintering can promote the sintering mineralization reaction.