20 October 2024, Volume 36 Issue 10

    

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  Preface to the special issue of refractories for advanced steel smelting and high-temperature alloy smelting in 2024

  Journal of Iron and Steel Research. 2024, 36(10): 1245-1246.

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Reviews
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  Research progress on characterization and evaluation of refractory damage behavior based on machine vision/hearing

  LIU Chenchen, HUANG Ao, LI Shenghao, CHEN Xinyu, GU Huazhi

  Journal of Iron and Steel Research. 2024, 36(10): 1247-1266. https://doi.org/10.13228/j.boyuan.issn1001-0963.20240167

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  As an essential fundamental material in high-temperature industries such as metallurgy and building materials, refractories inevitably endure chemical corrosion and mechanical fracture (collectively referred to as "damage") under coupled thermal-chemical-mechanical conditions during the period of service, resulting in the deterioration and wear of high-temperature furnace linings and affecting quality of the products. Conducting postmortem testing analysis methods to evaluate damage behavior presents challenges, as direct observation of the in-situ degradation process of refractories within high-temperature and complex environments is not feasible. The paucity of process information, particularly regarding the condition of thermal-chemical-mechanical coupling, can potentially skew the analysis outcomes. The research progress in the application of machine vision/hearing technologies in characterizing and evaluating the damage behavior of refractories was reviewed. It indicates that the application of digital image correlation (DIC) and acoustic emission (AE) techniques, which achieve non-contact real-time monitoring of the full-field strain and acoustic emission signals of refractories, can characterize the degradation evolution process under multi-factor coupling conditions. These techniques provide a novel approach for accurately revealing the damage mechanisms and evaluating the service performance of refractories. This research aims to provide theoretical support for the development of superior refractories for high-quality product smelting and production.
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  Current status of lightweight refractories prepared from industrial solid wastes and their metallurgical applications

  MU Xin, LI Guangming, ZHANG Chengcheng, LIU Yongli, SONG Na, MA Beiyue1

  Journal of Iron and Steel Research. 2024, 36(10): 1267-1274. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230276

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  A large amount of industrial solid waste containing high aluminum-silicon content was generated in China every year, which was expected to become the raw material for the preparation of lightweight refractories in the metallurgical industry. The research status of industrial solid waste such as tailings, metallurgical slag, dust sludge, fly ash, and coal gangue in the preparation of lightweight aggregates was summarized. The performance advantages of preparing lightweight refractories by using artificial aggregates instead of natural aggregates were compared and summarized. The relevant research on the microporosity of lightweight aggregates and the homogenization of the matrix in the preparation of lightweight refractories was summarized, clarifying the rationality and development prospects of using industrial solid waste aggregates to prepare lightweight refractories. The need for developing new processes and technologies for preparing lightweight refractories from solid waste aggregates, as well as continuously improving the thermal insulation performance and slag resistance of aluminum-silicon lightweight refractories, was proposed to achieve efficient utilization of industrial solid waste resources and the lightweight and functional development of high-performance refractories in metallurgy.
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  Research progress of lightweight refractories for smelting of advanced steel

  ZHANG Wei

  Journal of Iron and Steel Research. 2024, 36(10): 1275-1289. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230248

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  Refractories, as the high-temperature furnace lining for the smelting of iron and steel, play a crucial role in improving thermal efficiency and reducing energy consumption in the industry. In recent years, the research on lightweight refractories for the smelting of advanced steel has been paid extensive attention. Thus, the research progress of lightweight refractories for the smelting of advanced steel based on the types of lightweight refractories were reviewed, in order to guide the design and development of long-lived lightweight refractories and promote the energy conservation and emission reduction in high-temperature furnaces for the smelting of advanced steel. The lightweight of refractories can be achieved by the introduction of lightweight aggregates or the design of a density gradient structure. Lightweight refractories have low thermal conductivity and bulk density and good thermal insulation properties, which can be directly used as working linings. The preparation technology, types, and damage mechanism of lightweight refractories still need to be further studied.
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  Research progress on purification technology of calcium removal from magnesite and development and application of magnesia-calcium-based refractories

  WU Sheng, HOU Qingdong, LUO Xudong, MA Beiyue, WANG Peng, MAN Yiran

  Journal of Iron and Steel Research. 2024, 36(10): 1290-1297. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230228

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  Magnesite is an important mineral resource for industrial production. Due to the restriction of production process, a large number of low-grade magnesite cannot be effectively utilized. In order to improve the operation rate of this kind of magnesite purification process, the mechanism of action of inevitable ions, collectors and inhibitors on dolomite separation in the flotation process of magnesite was summarized, the influence of calcination temperature and raw material particle size on dolomite purification in the thermal separation process of magnesite was summarized, and the advantages and disadvantages of flotation/thermal separation process was analyzed. Finally, the application progress of magnesia-calcium-based refractories prepared by purified magnesite in the field of steelmaking was introduced.
Refractories Research
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  Effects of C/MgO composite powders with different morphologies of carbon on properties of low-carbon MgO-C refractory materials

  DING Donghai, GUAN Yue, LI Guodan, XIAO Guoqing

  Journal of Iron and Steel Research. 2024, 36(10): 1298-1307. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230091

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  The combustion synthesized C/MgO composite powder (CN0) and CNTs/MgO composite powder (CN1) were added to the low carbon MgO-C refractories, and the enhancement effects of composite powders with different morphologies of carbon on low-carbon MgO-C refractories were compared. The effect of composite powders on bulk density, apparent porosity, cold crushing strength, cold modulus of rupture, oxidation resistance, thermal shock resistance and slag resistance of low carbon MgO-C refractories was studied. The results show that the addition of the composite powder can reduce the apparent porosity of the refractories, where the apparent porosity of the specimen CM6 (12.5%) with CNTs/MgO composite powder added is 8.1% lower than that of the reference specimen CM0 (13.6%) and 8.8% lower than that of C/MgO composite powder added specimen M6. In addition, the addition of CNTs/MgO composite powder significantly improves the thermal shock resistance and residual strength of the refractories, where M6 shows the highest residual strength ratio but the lowest residual strength and CM6 presents the highest residual strength (2.5 MPa), which is 13.6% higher than that of CM0 (2.2 MPa). Meanwhile, the slag resistance of low carbon MgO-C samples with CNTs/MgO composite powder added is improved, with the best corrosion index of 1.09, which is 21.6% less than CM0 and 6.0% less than M6. The addition of CNTs/MgO composite powder can improve the oxidation resistance of refractory materials. The oxidation index of CM6 is 56.44%, which is 11.81% lower than that of CM0.
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  Deformation measured with baseline calibration method and its application in determination of compressive strength of fireclay bricks at elevated temperature

  ZHU Qingyou, CHENG Xu, YU Chao, ZHU Hongxi, YIN Yucheng, DENG Chengji

  Journal of Iron and Steel Research. 2024, 36(10): 1308-1317. https://doi.org/10.13228/j.boyuan.issn1001-0963.20240127

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  The coupling effect between temperature and stress can cause excessive deformation of refractory materials, thereby endangering the stability of the furnace lining structure. Therefore, accurate measurement of deformation is essential for designing and predicting furnace lifespan. The load softening temperature and creep rate are the main methods for evaluating the high-temperature compression deformation of refractories at low stress levels. However, applying these methods directly to high stress levels may lead to issues such as bent pins, broken pins, and gasket deformation. To address this challenge, a baseline calibration method based on the displacement recording function of the pressure machine for evaluating high-temperature compression deformation of refractories was proposed, and the principle and rationality of this method were elaborated in detail. According to the softening temperature of fireclay bricks, the high-temperature compressive strength was measured at different temperatures, and the measurement deviation was compared. The minimum deviation was 3.2%. By using CT technology to detect the internal pore distribution of the sample after the experiment, the closed-cell porosity increased from 3.43% to 8.10%. Combined with phase and typical morphology analysis, it further indicates that the baseline calibration method has high accuracy and practicality. Based on the experimental results, the judgment criteria and definition of high-temperature compressive strength were proposed, providing theoretical support for the research of refractory materials and the design of high-temperature furnace linings.
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  Damage of refractory castables based on 3D mesoscopic stochastic model

  HUANG Yufei, SU An, YANG Xin, ZHANG Yuanlu, HE Zhijun

  Journal of Iron and Steel Research. 2024, 36(10): 1318-1325. https://doi.org/10.13228/j.boyuan.issn1001-0963.20240181

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  The study of damage to refractory castables at the mesoscopic scale is significant for revealing damage′s evolution process and mechanisms. With the help of computer-aided technology, a 3D mesoscopic stochastic model program for refractory castables was meticulously crafted using Matlab, and a 3D mesoscopic stochastic model conforming to the particle size distribution of refractory castables was established in combination with the Comsol Multiphysics modeling. The model, subsequently, was transferred into Abaqus, and the maximum principal stress criterion was used as the crack initiation criterion to study the whole process of damage evolution of refractory castables. It is found that this model can capture the micro-crack propagation behavior across microscopic to mesoscopic scales. In the application process of refractory castables, microcracks usually start at the defects of the matrix part and expand rapidly in the 45° direction around the aggregate. The stress distribution at the tips of adjacent cracks between the matrix and the presence of aggregate can affect the propagation path of cracks, causing them to deflect around the aggregate and bend away from the aggregate particles. The result is consistent with the actual damage and failure results.
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  Effect of pore structure characteristics of lightweight alumina on material properties

  GUO Tongshuang, DING Jun, DENG Chengji, YU Chao, ZHU Hongxi

  Journal of Iron and Steel Research. 2024, 36(10): 1326-1335. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230256

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  To investigate the impact of porosity on material properties during the lightweighting process, porous alumina specimens with varying pore structure parameters were meticulously fabricated. Subsequently, the specimen′s pore structure was meticulously characterized utilizing advanced techniques like mercury intrusion porosimetry and CT scanning technology. Employing the grey theory, the repercussions of alterations in pore structure on material properties were systematically explored. The outcomes underscore a consistent trend: as porosity escalates, the bulk density of porous alumina registers a corresponding gradual reduction. Additionally, the compressive strength and thermal conductivity of the porous alumina exhibit noteworthy declines in tandem with increasing porosity. Importantly, it was observed that the distribution of pore sizes, particularly those smaller than 1.5 μm, wields a profound influence over both compressive strength and thermal conductivity. Conversely, the pore size distribution exceeding 150 μm exerts a notably milder impact on material properties. In essence, our findings underscore the importance of augmenting the proportion of pores with sizes falling below 1.5 μm during the material lightweighting process, as this strategy proves most efficacious in enhancing the overall material performance.
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  Sintering properties and Cr⁶⁺ reduction mechanism of aluminum- chromium refractories in HIsmelt reduction of ironmaking

  LI Jingjie, ZHANG Han, ZHAO Huizhong, LI Yuqi

  Journal of Iron and Steel Research. 2024, 36(10): 1336-1342. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230351

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  HIsmelt ironmaking process is known for its short process, wide applicability of raw materials, and high purity of products. It is an efficient, low-carbon and green ironmaking process that utilizes aluminum-chromium refractory materials for furnace lining. Using tabular corundum and aluminum-chromium slag as raw materials, aluminum dihydrogen phosphate as a binder, and silica micropowder as an additive, a sample of regenerated aluminum-chromium refractory material for HIsmelt smelting reduction ironmaking was prepared by forming under 150 MPa pressure and firing at 1 600 ℃ for 3 h. The influence of silica micropowder on the sintering performance and chromium valence state transformation of the sample was studied. The results show that the addition of silica micropowder can promote the sintering process and formation of aluminum-chromium solid solution to avoid the generation of Cr⁶⁺ compounds. The lattice constant of the aluminum-chromium solid solution increases with the addition of silica micropowder. Meanwhile, silica micropowder can reduce Cr⁶⁺ to Cr³⁺, reducing the concentration of Cr⁶⁺ in the specimen. A small amount of mullite will be generated in situ after adding silica micropowder, which will influence the thermal shock resistance and thermal expansion coefficient of the specimen. The appropriate amount of silica micropowder is 2-3wt.%.
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  Influence of CaZrO₃ introduction types and magnesium oxide content on properties of synthesized MgO-CaZrO₃ refractory materials

  KONG Yibo, SUI Xinyuan, WANG Zhipeng, WANG Liguang, YU Jingkun, YUAN Lei, WEN Tianpeng

  Journal of Iron and Steel Research. 2024, 36(10): 1343-1351. https://doi.org/10.13228/j.boyuan.issn1001-0963.20240214

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  To prepare high-performance MgO-CaZrO₃ refractory materials, pre-synthesized calcium zirconate was used as the raw material, and different contents of magnesium oxide were added during the process. The effects of CaZrO₃ introduction types and magnesium oxide content on the phase composition, microstructure and physical properties were studied through techniques such as X-ray diffraction, physical property analysis, and scanning electron microscopy. The results show that the presence ofMgO promotes the transformation of calcium zirconate to the intermediate product Ca_0.15Zr_0.85O_1.85 to a certain extent. During the high-temperature sintering process, newly generated CaZrO₃ could lead to the increase in interfacial reactions and the sintering densification would be greatly improved. When the pre-synthesized CaZrO₃ was introduced as well as 30 mass% of MgO was added, the obtained MgO-CaZrO₃ refractories possessed excellent properties. For the obtained MgO-CaZrO₃ refractories, the main phases were MgO, CaZrO₃, and Ca_0.15Zr_0.85O_1.85, where the average grain size of CaZrO₃ was 1.5-2.5 μm andthat of MgO was 2.5-3.5 μm. According to the analysis of densification parameters, the apparent porosity was 2.56%, the bulk density was 3.85 g/cm³, the linear shrinkage rate was 15.43%, and the compressive strength at room temperature was 376 MPa. Correspondingly,the MgO-CaZrO₃ refractories were obtained with excellent properties when the synthesized CaZrO₃ was introduced as well as 30 mass% of MgO was added. The main phases for the prepared MgO-CaZrO₃ refractories were also MgO, CaZrO₃, and Ca_0.15Zr_0.85O_1.85. The average grain size of CaZrO₃ and MgO increased to 2-4 μm and 9-11 μm, respectively. Meanwhile, the densification also increased, where the apparent porosity was 0.90%, the bulk density was 4.87 g/cm³ and the linear shrinkage rate was 17.47%. The room-temperature compressive strength exhibited a decrease tendency with a value of 250 MPa at this time.
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  Influence of calcium aluminate cement contents on properties and microstructure of light-fired corundum-spinel purging plugs

  CHEN Yu′e, ZHANG Peixiong, ZUO Xiaotan, ZHAO Li, WANG Enhui, HOU Xinmei

  Journal of Iron and Steel Research. 2024, 36(10): 1352-1360. https://doi.org/10.13228/j.boyuan.issn1001-0963.20230284

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  Calcium aluminate cement (CAC) contents and heat treatment temperature were the main factors affecting strength and thermal shock resistance (TSR) of light-fired steel ladle. The influence of heat treatment temperature (110-1 600 ℃) and CAC contents (1 wt.%-9 wt.%) on microstructure, phase composition, cold modulus of rupture (CMOR), cold crushing strength (CCS), high-temperature modulus of rupture (HMOR) and TSR of corundum-spinel castable were comprehensively studied. The results show that the CMOR and CCS of samples fired at 110-1 000 ℃ increase with the increase in CAC contents, whereas the CMOR and CCS of samples fired at 1 400 ℃ and 1 600 ℃ increase and subsequently decrease. The obtained samples with 5 wt.% CAC content have the highest CMOR and CCS values. The HMOR of sample fired at 1 600 ℃ increases firstly and then decreases with the increase in CAC contents (the HMOR is the best at 5 wt.%). The sample with 7 wt.% CAC contents obtains the optimal TSR performance. Therefore, the appropriate CAC addition of corundum-spinel light-fired ladle purging plugs is 5-7 wt.%.
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  Effect of thermal shock resistance of magnesia-carbon refractories by spherical MgO-C composite aggregate

  ZHAO Haohao, HAN Bingqiang, WEI Jiawei, MIAO Zheng, ZHONG Hutang

  Journal of Iron and Steel Research. 2024, 36(10): 1361-1368. https://doi.org/10.13228/j.boyuan.issn1001-0963.20240145

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  At present, the high carbon content in magnesia carbon refractories used in steel ladles can cause the carburization of the refractories into the molten steel and result in refractories with a high thermal conductivity, leading to significant heat loss. Reducing the carbon content will significantly decrease the thermal shock resistance of the material, while changing the way the carbon source is introduced can improve the performance of the material and provide possibilities for carbon reduction. In view of the above problems, a new method was proposed to the prepare spherical magnesium-carbon composite aggregates by the pellet granulation method and replace flake graphite to improve the thermal shock resistance of the material. The results show that the mechanical properties and thermal shock resistance of the materials are improved after the introduction of the spherical magnesium-carbon composite aggregate into the magnesium-carbon refractories. The flexural strength and fracture energy of the best substitution amount of refractories after heat treatment at 1 100 ℃ and 1 550 ℃ are increased by 27.93%, 15.17% and 4.12%, 8.84%, respectively. The thermal shock resistance and residual strength are increased by 9.15% and 0.8 MPa, respectively. Moreover, the crack propagation after thermal shock showed more through aggregate fracture, mainly due to the introduction of microcracks by the addition of spherical magnesium carbon composite aggregate and the tighter bonding between the aggregate and matrix caused by the in-phase sintering of the aggregate and matrix.