25 February 2026, Volume 38 Issue 2
    

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    Reviews
  • Effects of calcium treatment on non-metallic inclusions in Al-deoxidized steel
    LIU Zimeng, LI Wanming
    Journal of Iron and Steel Research. 2026, 38(2): 153-172. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250185
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    How to control Al2O3 oxide inclusions in Al-deoxidized steel has long been a challenging issue in metallurgical production. Calcium treatment can modify high-melting-point Al2O3 oxide inclusions into low-melting-point calcium aluminate (12CaO·7Al2O3), which effectively inhibits nozzle clogging and improves the hydrogen-induced cracking resistance of steel. However, parameters such as the timing and method of calcium addition directly affect the calcium yield and the degree of inclusion modification. Improper control may, on the contrary, exacerbate the nozzle clogging phenomenon. Therefore, the modification effect of calcium treatment on non-metallic inclusions in Al-deoxidized steel is reviewed. From the perspectives of kinetics and thermodynamics, the mechanism of action and key influencing factors are elaborated, including the effects of molten steel temperature, calcium addition method and timing, CaO/Al2O3 ratio of refining slag, as well as the contents of O, S and Al in molten steel on the compositional evolution and liquid phase fraction of inclusions. In addition,the technological optimization directions of calcium treatment is discussed, aiming to improve calcium utilization efficiency and inclusion control level, involving innovative approaches such as secondary calcium treatment, application of calcium-silicon iron, and calcium-magnesium alloy synergism.
    • Smelting and Working
  • Effects of K, Na, KF and NaF gases on hot-state properties and microstructure of coke
    SUN Quan, LUO Guoping, CAO Linxiang, WANG Ziwei, BAI Xiaoguang, LIU Shuguang, LIU Jingquan
    Journal of Iron and Steel Research. 2026, 38(2): 173-185. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250157
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    Aiming at the degradation mechanism of coke induced by K, Na, KF and NaF gases during blast furnace smelting, gas adsorption experiments on coke were conducted via the gas-phase adsorption method. Combined with characterization techniques including XRD and SEM-EDS, the influence laws of K, Na, KF and NaF gases on the hot-state properties and microstructures of coke were systematically investigated. The results show that coke surface particles are exfoliated under the action of K gas, while powder-like spalling of coke surface is induced by Na gas. In contrast, the number of pores in coke is significantly increased by KF and NaF gases. After the adsorption of K, Na, KF and NaF gases by coke, the interplanar spacing of the (002) crystal plane of graphite microcrystals is enlarged, whereas the microcrystalline stacking height and microcrystalline layer size are reduced, which severely impairs the orderliness and integrity of the microcrystalline structure. The degradation degree of the aforementioned gases on the microcrystalline structure is ranked as follows: K>Na>KF>NaF. The variation of microcrystalline structure leads to an increase in coke porosity, which in turn elevates the coke reactivity index (CRI) and reduces the coke strength after reaction (CSR). Among these gases, the effects of K and Na gases on coke porosity are significantly stronger than those of KF and NaF gases. Specifically, the influence of K gas is greater than that of Na gas, and the impact of KF gas exceeds that of NaF gas. When coke is adsorbed with 1% NaF gas, its hot-state properties (with CRI≤25% and CSR≥65%) still meet the requirements for blast furnace smelting. However, after the adsorption ofmass fraction of 1% K, Na, or KF gas, both CRI and CSR exceed the standard limits. Overall, the influence degree of various gases on the hot-state properties of coke follows the sequence: K>Na>KF>NaF. In addition, with the increase in gas adsorption capacity, the growth rate of CRI and the decline rate of CSR both exhibit a trend of marginal decrease.
  • High-temperature performance evolution and consolidation mechanism of zinc-bearing iron dust-mud agglomerates
    WANG Guangwei, TAO Xuan, ZHU Yongjun, WANG Chen, WEI Kang, NING Xiaojun
    Journal of Iron and Steel Research. 2026, 38(2): 186-194. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250151
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    Eight types of zinc-bearing iron dust and sludge generated from iron and steel production processes were used as main raw materials, and agglomerates were prepared by adding different types of binders. Under simulated rotary hearth furnace process conditions, the evolution law and influence mechanism of compressive strength of agglomerates during the roasting-reduction process were systematically investigated. Results indicated that inorganic binders could effectively stabilize the initial structure of agglomerates and promote the formation of low-melting-point compounds, thereby improving the compactness and high-temperature compressive strength of agglomerates (the high-temperature strength could reach 3 309 N at 1 250 ℃). However, the agglomerates pre-pared with inorganic binders exhibited poor room-temperature performance with a strength of only 331 N, and the gangue components introduced by binders would reduce the iron grade of agglomerates. Agglomerates prepared with organic binders showed excellent room-temperature performance, with the room-temperature compressive strength reaching 467 N. Nevertheless, intense pyrolysis reactions of organic components occurred during high-temperature roasting, leading to a significant increase in the porosity inside the roasted agglomerates and a substantial decrease in high-temperature compressive strength. Composite binders efficiently connected the key links of low-temperature strength maintenance and high-temperature strength regeneration of agglomerates, effectively alleviated the expansion phenomenon during the reduction process, significantly improved the compactness and overall strength of agglomerates throughout the whole roasting-reduction cycle, and thus demonstrated excellent potential for comprehensive application.
  • Strengthening iron ore pellet consolidation by collaborative optimization of ore blending and high-pressure roll grinding
    WEN Xiaoping, XIE Luben, LIU Baixiang, YANG Yongbin, WANG Lin, YANG Zhongyu
    Journal of Iron and Steel Research. 2026, 38(2): 195-204. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250146
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    Iron ore pellet production is recognized as an energy-intensive and high-emission industrial process, and its energy conservation and emission reduction represent a critical component for the iron and steel industry to achieve the “dual carbon” goals. Efforts are made herein to leverage the synergistic effect of high-pressure roll grinding pretreatment and optimized ore blending, thereby reducing the pellet induration temperature while ensuring product quality, so as to provide technical support for the green transition of the iron and steel industry. A systematic laboratory experimental approach was adopted. Firstly, six types of iron concentrates were pretreated using a high-pressure roll mill under a pressure of 14 MPa, and the effects of this process on raw material particle size, specific surface area and pelletizing performance were analyzed. Subsequently, green pellets were prepared by a disc pelletizer, and the preheating and induration processes were simulated in a horizontal tube electric furnace to explore the influence law of different process parameters on pellet strength. Finally, scanning electron microscopy was employed to analyze the microstructural changes of pellets, thus revealing the synergistic strengthening mechanism.Results demonstrate that high-pressure roll grinding can significantly improve the physical properties of iron concentrates. After two passes of roll grinding treatment, the proportion of the 5 mm size fraction in the blended ore can be increased to 75.45%, which effectively enhances particle surface activity and strengthens recrystallization interface reactions, thereby improving pellet strength. Meanwhile, two passes of high-pressure roll grinding can substantially reduce the pellet induration temperature from 1 200 to 1 100 ℃. On this basis, optimized ore blending was further applied to enhance pellet consolidation efficiency. Under the optimal ore blending ratio (5 wt.% ore A, 11 wt.% ore C and 7 wt.% ore D), the minimum induration temperature of pellets can be further reduced to 1 080 ℃, with the compressive strength reaching 3 189 N/P, which far exceeds the industrial standard of 2 500 N/P. Microstructural analysis indicates that the synergistic effect of high-pressure roll grinding and optimized ore blending significantly enhances the recrystallization and intergrowth degree of hematite, reduces internal pores and cracks of pellets, and thus greatly improves structural compactness. The synergistic mechanism of high-pressure roll grinding and optimized ore blending was clarified, and the dual optimization effects of this combined technology on reducing induration temperature and improving pellet strength were quantified via laboratory data.
  • Changes of gas-slag-metal multiphase flow characteristics at different stages during converter blowing process
    HOU Fuqing, LÜ Ming, LI Xinhang, GUO Hongmin, LIN Xueliang, LIANG Shaopeng
    Journal of Iron and Steel Research. 2026, 38(2): 205-215. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250159
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    Gas-slag-metal three-phase emulsification is promoted by blowing gas into the molten pool in converter steelmaking process. During the blowing process, slag formation, dephosphorization, decarburization and heating are achieved. In order to explore the changes in gas-slag-metal multiphase flow characteristics at different stages of converter blowing, a three-dimensional full-scale model of a 120 t top and bottom combined blowing converter was established. Based on parameters such as oxygen lance position, bottom blowing intensity, molten pool composition, and temperature during the blowing process, the stirring energy, jet characteristics, slag-metal interface characteristics, molten pool velocity, and wall shear stress changes at different stages were studied. The results show that in the early stage of blowing, the lance is positioned high, and the oxygen jet mainly acts on the slag phase. The slag surface fluctuation intensity is 1.27, the area where the molten metal surface velocity exceeds 1 m/s is 9.36 m2, and the stirring energy density of the molten pool is 2 333.21 W/t. In the middle and middle-late stages of blowing, the lance is lowered, the impact area of the oxygen jet decreases, and the bottom blowing intensity weakens. The jet′s action shifts from the slag surface to the molten metal, leading to an intense carbon-oxygen reaction. The slag surface fluctuation intensity increases, the area where the molten metal surface velocity exceeds 1 m/s decreases, and the stirring energy density of the molten pool decreases. In the late stage of blowing, the lance is lowered to 1.35 m, the bottom blowing intensity increases, and the jet impact depth on the molten pool further increases. The slag surface fluctuation intensity decreases to 1.32, the area where the molten metal surface velocity exceeds 1 m2 decreases to 8.15 m2, and the stirring energy density of the molten pool increases to 2 996.36 W/t. The wall shear stress in the gas-slag-metal three-phase interaction region is relatively concentrated. As blowing progresses, the maximum wall shear stress region gradually moves downward. In this region, the refractory material suffers severe erosion. From the early to the late stage of the blowing process, the maximum wall shear stress corresponding to the four stages is 2.80, 3.31, 3.56, and 3.81 Pa, respectively.
  • Design optimization of plasma generator for refractory metal purification
    DU Mengshuai, PENG Junlei, HE Shengya, YU Sheng, LI Chuanjun
    Journal of Iron and Steel Research. 2026, 38(2): 216-228. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250167
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    High-purity refractory metals are recognized as critical raw materials supporting the development of the advanced electronic information industry. However, mainstream purification methods such as electron beam melting and plasma arc melting are generally plagued by technical limitations, including limited removal efficiency of gaseous impurities and high susceptibility of electrodes to contamination. Inductively coupled plasma melting (ICPM) technology is proven to effectively overcome these drawbacks, thus emerging as a highly efficient and clean purification approach. As the core component of ICPM equipment, the rationality of the structural design of the plasma generator directly determines the stability and continuity of the ICPM purification process. Therefore, numerical simulations are first carried out via Fluent software to optimize the key structural parameters of the generator. Results demonstrate that a stable and symmetrical vortex zone as well as an optimal flow field with uniform cooling can be formed inside the generator when the number of central gas inlet holes is set to 8, the incident angle of the inlet holes is 8°, and the diameter of the cooling gas inlet slot is 6 mm. Furthermore, a magneto-thermal-fluid multi-field coupling model is established by means of COMSOL software to investigate the influence laws of process parameters (including coil power, central gas flow rate and cooling gas flow rate) on the plasma temperature field and flow field. It is found that the enhancement of coil power and central gas flow rate can significantly strengthen the plasma jet intensity and elevate its temperature. In contrast, a critical threshold exists for the cooling gas flow rate; beyond this threshold, a further increase in the flow rate will instead lead to the reduction of plasma jet intensity and temperature. Results of experimental verification indicate that the plasma generator designed achieves stable operation, and the measured morphology of the plasma torch shows high consistency with the simulation results. Conclusions drawn from the work are expected to provide scientific basis and technical support for the engineering design of plasma generators for ICPM equipment.
  • Application of compound control strategy based on temperature fluctuation in hot tandem rolling AGC system
    LI Xuezhi, LI Boqun, WANG Peng, CUI Yang
    Journal of Iron and Steel Research. 2026, 38(2): 229-238. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250168
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    The advancement of rolling technology relies on robust technical support, while the current control level has entered a critical turning point. The control effect based on traditional control theories has approached its limit, and numerous key technical problems have not yet been completely resolved. Therefore, it is imperative to introduce brand-new control theories and methods to achieve leapfrog improvement in control performance. In the hot-rolled strip production process, the automatic gauge control of the finishing rolling process occupies a core position, and its control accuracy directly determines the quality and qualification rate of the finished strip. To address the influence of temperature fluctuations on the stability of the exit thickness of incoming materials and the positive feedback problem existing in the traditional gauge feedback control, a hardness feedforward control strategy is proposed. Taking the Ansteel 1700 ASP production line as the application object, the influence coefficients of load distribution on various process indicators are calculated and analyzed; meanwhile, based on the increment equations of thickness, rolling force and crown, the roll gap adjustment values of the F3—F6 stands are determined. In hot rolling field practice, the hardness feedforward control of the F3 and F4 stands and the hardness over-compensation control of the F5 stand are successfully realized. In addition, a nonlinear PID control strategy is introduced into the monitoring AGC system, which features a wide parameter tuning range and strong engineering practicability. Statistical analysis of production data of different rolling specifications shows that after the implementation of the composite control strategy, the strip thickness accuracy is improved by approximately 1% compared with the original level, indicating that the control system has good prospects for popularization and application.
    • Materials Research
  • Effect of strip entry temperature on interfacial layer and coating microstructure of galvanized sheet
    ZHANG Kunlong, QIU Liang, LU Jun, WANG Shuize
    Journal of Iron and Steel Research. 2026, 38(2): 239-250. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250166
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    Experiments were carried out to investigate the influence of strip entry temperature on interface reaction and microstructure of alloyed coatings. Industrial IF steel and DP980 steel were used as substrates to simulate hot galvanizing process in a zinc bath containing 0.13%(mass fraction)Al. The experimental results showed that the leakage plating of DP980 steel was severe and became more pronounced with increasing temperature, with the least severe leakage plating at 470 ℃. The IF steel coating quality remained good under all conditions. When the temperature is low, the interface forms dense and fine ζ phase. With the increase of temperature, the ζ phase coarsens and the δ phase increases. The peak value of interface aluminum enrichment decreases with the increase of temperature, and the enrichment degree of IF steel is higher. The interface aluminum enrichment of DP980 steel is weak due to the dense Mn/Si oxide on the surface. After alloying annealing, the interface aluminum enrichment of the low temperature sample is strong, and the alloying is incomplete; with increasing the pot temperature, the iron content of the coating increases, and the iron content is the best at 470 ℃. At 530 ℃, there is too thick Γ phase over-alloying. Experiments show that temperature of strip into pot affects the quality of the coating and the degree of alloying by regulating the interface aluminum enrichment and Fe-Zn phase transformation.
  • Dissolving behavior of carbide in Nb-Mo-V-Ti and Nb-Mo-V microalloyed high-strength invar steel
    LIU Xueting, CHEN Shuai, LI Jiachong, DI Yanjun, YU Yanchong
    Journal of Iron and Steel Research. 2026, 38(2): 251-265. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250156
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    The low thermal expansion properties of invar steel make it widely used in precision instruments, aerospace components and other fields, but the low strength limits its further development. Adding alloying elements to invar steel and inducing the precipitation of carbide second phase through solid solution-aging can significantly improve the mechanical properties of invar steel.Solid solution-aging is a key prerequisite for precipitation, and carbide dissolution behavior in this process is particularly important. The alloying elements Nb, Mo, V and Ti were added to invar steel, and the carbide dissolving behavior was analyzed and the mechanism was investigated by scanning electron microscopy and high-temperature laser confocal microscopy. The results show that there are two types of carbides in Nb-Mo-V-Ti and Nb-Mo-V invar steels. The larger carbide particles with an average size greater than 5 μm, formed during the solidification process, are called as the primary carbides. The smaller carbides with an average size of less than 1 μm, precipitated from the matrix, are called as the secondary carbides. Both types of carbides are compositeprecipitation phasesof (Nb, Mo, V)C or (Nb, Mo, V, Ti)C corresponding to their respective components. The thermodynamic results and HT-CSLM observation indicate that the dissolution temperature of the primary carbides is close to the solidification transition temperature of the invar steel, so that it is difficult to dissolve. The secondary carbides realize the basic dissolution after heating and prolonging the holding time, and from this, Ti has a hindering effect on the dissolution of the carbides, which makes the carbides have a higher thermal stability. In addition, the Johnson-Mehl-Avrami-Kolmogorov equation is used to characterize the dissolution kinetics of the secondary carbides, and the dynamics model is experimentally verified to be able to predict the dissolution fraction of the secondary carbides better.
  • In situ observation of reheated austenite grain growth and bainite transformation in DH36 ship plate steel
    QIN Yulong, ZENG Jie, WANG Zichao, WANG Wanlin, XIAO Xiong, YANG Yan
    Journal of Iron and Steel Research. 2026, 38(2): 266-275. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250152
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    The evolution of microstructure during heating, holding, and cooling stages directly determines the mechanical properties of steels. To achieve effective microstructural control during slab hot rolling, the high-temperature confocal laser scanning microscope is used for in situ observation of austenite grain growth behavior in DH36 ship plate steel during heating/holding stages and phase transformation evolution under different cooling rates. The results demonstrate that austenite grain size increases significantly with the elevated heating temperatures and prolonged holding time.When the heating temperature is in the range of 1 150-1 200 ℃, the average austenite grain size is 30.6-42.4 μm. When the heating temperature is raised to 1 250 ℃, the austenite grains grow significantly, reaching an average size of 253.4 μm.The grain growth exhibited a two-stage pattern: rapid growth during the initial holding period (0-5 min), followed by a significant decrease in the growth rate until it stabilized (5-30 min). A kinetic model for austenite grain growth was established based on these findings. Furthermore, room-temperature microstructures show marked variations under different cooling rates (360 and 720 ℃/min). At 360 ℃/min, granular bainite dominates the microstructure, while increasing to 720 ℃/min yields predominantly lath bainite. Bainite primarily nucleates along austenite grain boundaries, with additional nucleation modes observed including intragranular nucleation at inclusions and nucleation at broad sides of pre-existing bainite plates.
  • Effect of tempering process on microstructure and impact toughness of 35Cr16Cu3Mo2VN steel
    YAN Yitong, LI Quan, GONG Zhihua, BAO Hansheng, LI Wei
    Journal of Iron and Steel Research. 2026, 38(2): 276-285. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250124
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    The 35Cr16Cu3Mo2VN martensitic stainless steel was subjected to tempering treatment, and the effects of different tempering temperatures (500-650 ℃) on its microstructure and mechanical properties were systematically analyzed. The results indicated that as the tempering temperature increased, the impact toughness of the tested steel significantly rose from 2 to 17 J before reaching a stable level, while the hardness decreased monotonically. A critical transition occurred at 530 ℃, where the tested steel exhibited a notable increase in toughness while maintaining a hardness of 55HRC, achieving optimal overall performance. Within the tempering temperature range, the impact toughness of the 35Cr16Cu3Mo2VN steel is improved.On the one hand, this is due to the synergistic effect of the precipitation and growth of M2C carbides, along with the reduction in the size ofM23C6 carbides.On the other hand, the transformation of the matrix microstructure. The decrease in hardness with increasing the tempering temperature was due to carbon precipitation and agglomeration at high temperatures, which reduced the solid solution strengthening effect of carbon and thus was harmful for the material′s hardness.
  • Effect of welding current on microstructure and mechanical properties of Q690D high-strength steel welded joints
    LIU Chenglong, SUN Youping, HOU Guoqing, HE Jiangmei, LI Wangzhen
    Journal of Iron and Steel Research. 2026, 38(2): 286-298. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250169
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    Welding experiments were conducted on 10 mm-thick Q690D high-strength steel using CO2 gas shielded welding. The effects of welding current on the microstructure and properties of welded joints were investigated by means of optical microscopy, scanning electron microscopy, and SmartLab SE X-ray diffractometer. The results show that the microstructures of different regions in the welded joint vary significantly, where the weld metal zone is dominated by acicular ferrite, while the coarse-grained heat-affected zoneand fine-grained heat-affected zone consist of lath martensite and bainite. Meanwhile, the partially recrystallized heat-affected zone exhibits significant softening, which is attributed to the ferrite-bainite mixed microstructure and low dislocation density. As the welding current increases, the recrystallization degree and dislocation density in the weld metal zone first increase and then decrease. At the optimal welding current of 260 A, the welded joint achieves the best mechanical properties. Although the microhardness distribution shows regional differences, the average hardness remains at a relatively high level. The tensile strength and elongation reach 724.50 MPa and 16.08%, respectively. The fracture surface displays a large number of dimples, but quasi-cleavage features are also observed locally, indicating that the joint fracture mode is a ductile-brittle mixed fracture.
  • Analysis of hot ductility of Ni-Cr-Al alloy
    WANG Dehong, ZHANG Yijie, CHEN Linjun, DING Jian, XIA Xingchuan
    Journal of Iron and Steel Research. 2026, 38(2): 299-304. https://doi.org/10.13228/j.boyuan.issn1001-0963.20250194
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    The thermal tensile test of cast Ni-Cr-Al alloy within the temperature range of 950-1 200 ℃ and strain rate of 0.25 s-1 was conducted by using Gleeble-3800 thermal simulation test machine, and the evolution law of hot ductility was analyzed by combining fracture morphology and microstructure. The results show that tensile strength decreases with the increase in the temperature, and reduction of area increases first and then decreases. The reduction of area at the temperature range of 1 000-1 150 ℃ is more than 75%, which shows excellent hot ductility. The microstructure shows that the ductility is poor at 950 ℃ due to low temperature, the ductility is improved with the increase in the temperature, and the formation of recrystallized organization is conducive to ductility enhancement at 1 050-1 150 ℃. However, the ductility deteriorated drastically at 1 200 ℃, which was attributed to the segregation of P and Zr elements at grain boundaries, leading to the weakened grain boundaries and the initiation of intergranular cracks.
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