2024年, 第31卷, 第5期　刊出日期：2024-05-25

  

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  Application of deep learning in iron ore sintering process: a review

  Yu-han Gong, Chong-hao Wang, Jie Li, Muhammad Nasiruddin Mahyuddin, Mohamad Tarmizi Abu Seman

  钢铁研究学报(英文版). 2024, 31(5): 1033-1049.
  https://doi.org/10.1007/s42243-024-01197-3

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  In the wake of the era of big data, the techniques of deep learning have become an essential research direction in the machine learning field and are beginning to be applied in the steel industry. The sintering process is an extremely complex industrial scene. As the main process of the blast furnace ironmaking industry, it has great economic value and environmental protection significance for iron and steel enterprises. It is also one of the fields where deep learning is still in the exploration stage. In order to explore the application prospects of deep learning techniques in iron ore sintering, a comprehensive summary and conclusion of deep learning models for intelligent sintering were presented after reviewing the sintering process and deep learning models in a large number of research literatures. Firstly, the mechanisms and characteristics of parameters in sintering processes were introduced and analysed in detail, and then, the development of iron ore sintering simulation techniques was introduced. Secondly, deep learning techniques were introduced, including commonly used models of deep learning and their applications. Thirdly, the current status of applications of various types of deep learning models in sintering processes was elaborated in detail from the aspects of prediction, controlling, and optimisation of key parameters. Generally speaking, deep learning models that could be more effectively implemented in more situations of the sintering and even steel industry chain will promote the intelligent development of the metallurgical industry.
论著
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  Difference in microstructural characteristics of stamp-charged coke and gravity-charged coke with approximate macroscopic performance

  Chong Zou, Zheng-yan Huang, Jian-yun Li, Bin Li, Shi-wei Liu, Yuan She

  钢铁研究学报(英文版). 2024, 31(5): 1050-1062.
  https://doi.org/10.1007/s42243-023-01118-w

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  The microstructural characteristics including optical texture, porosity and pore structure and chemical structure of stampcharged coke (SCC) and gravity-charged coke (GCC) with similar conventional macro-indicators were investigated, and the properties including micro-strength, reactivity of coke matrix and that after alkali enrichment were comparatively studied by various characterization methods. The anisotropic structure of SCC is composed of high content of fine mosaic texture, while the content of medium mosaic texture, coarse texture and fibrous texture is low. The statistical average shows that the fine mosaic average of SCC (24.89%) is 3.78 times the GCC average (6.58%), and the coarse mosaic average (1.24%) is only about 1/3 of the GCC average (3.43%). The porosity of SCC is lower than that of GCC, but tamping process does not lead to the fact that the number of closed pores of SCC is significantly lower than that of GCC. Although the structure of SCC is compact, its pore number is large and the pore wall is thin. Pores of coke with diameter less than 150 nm seem unaffected by tamping process. The aromatic structure of SCC was less ordered than that of GCC, which was speculated to be related to the addition of more low metamorphic coal in coking. The microscopic strength and structural strength of SCC are lower than those of GCC. The reactivity of coke matrix is affected by the specific surface area, but it is not the determining factor of its macro-reactivity. The improvement in dissolution reactivity of coke after potassium enrichment is independent of coke type.
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  Super-high bed sintering for iron ores: problems ascertainment

  Liang-ping Xu, Hui-bo Liu, Yu-chao Zhao, Qiang Zhong, Zhong-lin Dong, Guang-hui Li, Tao Jiang

  钢铁研究学报(英文版). 2024, 31(5): 1063-1070.
  https://doi.org/10.1007/s42243-023-01074-5

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  Super-high bed sintering process is an important development direction of iron ore sintering for its lower emission and higher yield. However, there is a lack of deep understanding of the uneven quality of super-high bed sintering products, and the deterioration of reduction disintegration performance, the thickening of hearth layer and the reduction in energy-saving effect are perplexing enterprises and researchers. To ascertain the problems of super-high bed sintering, ten sintering machines with the areas of 265, 280, 360, 550 and 660 m2 and bed depth above 900 mm were sampled and analyzed. The results showed that problems were mainly shown in the unevenness of chemical composition, macrostructure, mechanical strength and metallurgical performance. The chemical composition exhibits severe segregation in both horizontal and vertical directions, with basicity segregation reaching as high as 0.81. The uneven macrostructure of sinter is reflected in a 10% difference in porosity and mechanical strength increase in 16%–19% along the vertical direction. The reducibility and reduction disintegration performance gradually deteriorate along the bed depth, with a difference of 10.5% in reducibility and 7.3% in RDI_{-0.5 mm} (reduction disintegration index of sinter with size smaller than 0.5 mm).
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  Influence of oxygen-rich hot air composite gas medium on sintering performance and function mechanism

  Min Gan, Hao-xiang Zheng, Xiao-hui Fan, Zhi-yun Ji, Qiang Li, Ming Wu, Yi-fan Wang, Xiao-long Wang, Yu-feng Wu, Xu-ling Chen, Zeng-qing Sun, Xiao-xian Huang

  钢铁研究学报(英文版). 2024, 31(5): 1071-1081.
  https://doi.org/10.1007/s42243-023-01127-9

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  Hot air sintering technology is used to improve the quality and production efficiency of sintered ore. However, the current thick layer condition highlights the disadvantage of the low oxygen potential of the hot air sintering layer. Therefore, it is considered to use oxygen enrichment sintering to improve the environment of hot air sintering. Traditional sintering, hot air sintering, and oxygen-rich hot air sintering were compared through sintering cup experiments, and the influence of hot air and oxygen-rich hot air on sintering indexes was clarified. Hot air reduced the vertical sintering velocity, while improved the yield and tumbler index. Oxygen-rich hot air sintering contributed to improving the vertical sintering velocity while ensuring the quality of sintered ore, thus comprehensively improving production efficiency. Under the action of hot air, the highest temperature of the sintering layer increased and the high-temperature holding time was prolonged. After oxygen enrichment, the combustion efficiency of fuels in the upper layer of materials was promoted, which optimized heat distribution in the middle and lower layers of materials and increased the content of calcium ferrite in the sintered ore, thus strengthening the sintering process.
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  Proposing a machine learning approach to analyze and predict basic high-temperature properties of iron ore fines and its factors

  Qing-ke Sun, Yao-zu Wang, Jian-liang Zhang, Zheng-jian Liu, Le-le Niu, Chang-dong Shan, Yun-fei Ma

  钢铁研究学报(英文版). 2024, 31(5): 1082-1094.
  https://doi.org/10.1007/s42243-023-01096-z

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  The basic high-temperature properties of iron ore play a crucial role in optimizing sintering and ore blending, but the testing process for these properties is complex and has significant lag time, which cannot meet the actual needs of ore blending. A prediction model for the basic high-temperature properties of iron ore fines was thus proposed based on a combination of machine learning algorithms and genetic algorithms. First, the prediction accuracy of different machine learning models for the basic high-temperature properties of iron ore fines was compared. Then, a random forest model optimized by genetic algorithms was built, further improving the prediction accuracy of the model. The test results show that the random forest model optimized by genetic algorithms has the highest prediction accuracy for the lowest assimilation temperature and liquid phase fluidity of iron ore, with a determination coefficient of 0.903 for the lowest assimilation temperature and 0.927 for the liquid phase fluidity after optimization. The trained model meets the fluctuation requirements of on-site testing and has been successfully applied to actual production on site.
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  Energy saving analysis for CO2–O2 mixed injection technology in converter steelmaking

  Bao-chen Han, Chun-liang Gao, Ya-qiang Li, Dan Liu, Guang-sheng Wei, Rong Zhu

  钢铁研究学报(英文版). 2024, 31(5): 1095-1103.
  https://doi.org/10.1007/s42243-023-01170-6

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  Energy-saving in China’s iron and steel industry still relies on the development and improvement of short-term energy saving technologies. Therefore, a special converter smelting technology incorporating energy saving was proposed. To evaluate the energy-saving potential of the CO₂–O₂ mixed injection (COMI) technology, collected production data were used to develop an improved techno-economic model. Calculations reveal that the technology can save energy through auxiliary material consumption, sensible heat of solid by-product, iron loss reduction, and energy recovery. The application of COMI technology in an enterprise is cost effective, involving the energy saving potential of 0.206 GJ/t, the cost of conserved energy of - 48.83 yuan/GJ, and a simple payback period of 0.35 year for a 60-million-yuan investment. Sensitivity analysis shows that the investment cost and discount rate primarily influence the cost of conserved energy of the technology. As the discount rate increased, the cost of conserved energy also gradually increased. Overall, the COMI technology is an energy-saving technology with good development prospects.
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  Formation of free-surface vortex and vortex suppression by rotating stopper-rod at end of tundish casting

  Qing Fang, Peng Zhao, Hua Zhang, Wen-hao Zhou, Gang Yu, Jia-hui Wang, Hong-wei Ni

  钢铁研究学报(英文版). 2024, 31(5): 1104-1116.
  https://doi.org/10.1007/s42243-023-01150-w

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  A rotating stopper-rod technique was proposed to suppress the formation of free-surface vortex in the tundish. The large eddy simulation model coupled with volume of fluid model was developed to study the steel–slag–gas three-phase flow behavior. The critical slag entrapment height of the free-surface vortex and mass of residual steel were predicted at different rotating speeds (30, 60, 90 and 120 r/min) of the rotating stopper-rod. The numerical model was verified by water model experiment. The results showed that by rotating the stopper-rod in the opposite direction of the vortex above the submerged entry nozzle, the formation of vortex can be effectively disturbed and the critical height of the free-surface vortex can be reduced. Particularly for the 2nd strand, when the rotating speeds are 30, 60, 90 and 120 r/min, the critical height of the free-surface vortex above the 2nd strand is 7.3, 4.7, 6.3 and 7.4 cm, respectively. A reasonable rotating speed should be 60 r/min, which can reduce about 2 tons of residual steel. Other rotating speeds just can reduce about 1.6 tons of residual steel.
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  Numerical simulation of fluid flow and free surface fluctuations during wheel and belt casting process

  Kun Gao, Yan Peng

  钢铁研究学报(英文版). 2024, 31(5): 1117-1126.
  https://doi.org/10.1007/s42243-023-01116-y

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  The unstable fluid flow and severe free surface fluctuations in the wheel and belt caster can affect the quality of the cast bar. The lower level height tends to entrap inclusions in the molten metal. On the other hand, the higher level height makes the production process more dangerous due to the overflow of high temperature fluid from the mold. A computational model of the molten metal pouring process was established. The transient fluid flow and free surface fluctuations behavior were calculated using the three-dimensional large eddy simulation model and the volume of fluid model. The results show that the flow velocity of the main jet gradually decreases under the influence of the low kinetic energy fluid in the mold. There is an obvious oscillation in the tail of the jet, while the flow field is asymmetric in space. The jet is closer to the inside radius side due to the Coanda effect, and there is a recirculation zone on the inside radius and the outside radius respectively, according to the 10 s time-averaged results. Compared with the industrial observation and simulation results, the shape of the free surface is a wave that varies with time. In addition, the free surface height is lowest and the flow velocity is highest in the region near the jet.
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  Effect of solidification mode on microstructure evolution and properties of magnesium alloy with long-period stacking ordered phase

  Hao Li, Hong-mei Chen, Xu Zhang, Qian-hao Zang, Jing Zhang2, Di Feng, Yan-xin Qiao, Yu-hang Guo

  钢铁研究学报(英文版). 2024, 31(5): 1127-1138.
  https://doi.org/10.1007/s42243-023-01071-8

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  The solidification methods of electromagnetic stirring (EMS) and non-electromagnetic stirring were employed to prepare Mg–6Gd–3Y–xZn–0.6Zr (x = 1, 1.5, 2, 3) alloys. The evolution of alloy microstructures and the changes in properties were analyzed for different Zn contents. It has been observed that in alloys without electromagnetic stirring, as the Zn content increases, the alloy structure gradually refines. The primary second phase transitions from Mg5RE phase to long-period stacking ordered (LPSO) phase, resulting in improved hardness and elongation. In alloys subjected to electromagnetic stirring, there is a relatively higher content of the second phase, primarily consisting of LPSO phase. After applying electromagnetic stirring, the quantity and the type of LPSO phase in the alloy change. The alloy structure becomes more uniform with electromagnetic stirring, resulting in increased hardness and reduced hardness gradients within the grains. The mechanical properties of alloys with electromagnetic stirring are superior to those without electromagnetic stirring.
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  Correlation between longitudinal crack occurrence and mold heat transfer in continuous casting based on process data mining

  Zhi-qiang Peng, Zi-bing Hou, Kai Yi, Kun-hui Guo, Dong-wei Guo, Guang-hua Wen

  钢铁研究学报(英文版). 2024, 31(5): 1139-1152.
  https://doi.org/10.1007/s42243-023-01109-x

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  The correlation between the longitudinal crack occurrence and integrated heat transfer of the mold with data mining methods was investigated. Firstly, three kinds of support vector machine models based on principal component analysis with different input features were established to explore the effect of integrated heat transfer on the accuracy of the prediction model for the longitudinal crack. The results show that the accuracy was improved while features including mean and standard deviation of integrated heat transfer were added. Then, the difference in integrated heat transfer between defect and normal samples under the same process parameters was quantitatively compared. Compared with normal samples, the temperature difference of cooling water for defect samples decreased by 0.65%, and the temperature difference fluctuation increased by 31.1%. Finally, the literature data were used to provide support for the quantitative correlation according to defect formation mechanism. A new criterion for the prediction of longitudinal crack and a discovering method for correlation between product quality and process parameters in the manufacturing industry have been provided.
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  Reaction mechanism between Al2O3–MgO refractory materials and rare earth high-carbon heavy rail steel

  Yi Wang, Guang-jie Song, Ping Shen, Jian-zhong He, Da-xian Zhang, Jian-xun Fu

  钢铁研究学报(英文版). 2024, 31(5): 1153-1163.
  https://doi.org/10.1007/s42243-023-01147-5

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  Submerged entry nozzle (SEN) clogging is a major problem affecting the production quality of rare earth steel, and finding a suitable refractory outlet can significantly reduce production costs. To explore the relationship between refractory composition and interface interaction, unprotected coated Al₂O₃–MgO refractories and SiO₂-coated Al₂O₃–MgO refractories were added to rare earth high-carbon heavy rail steel under laboratory conditions, and the Al₂O₃–MgO refractory was found to be more suitable. The results show that, from the epoxy resin side to the refractory side, the contour of the refractory interface reaction layer can be divided into two main layers: an iron-rich reaction layer and an iron-poor reaction layer. Calculations based on the spherical model suggest that the adhesion force is proportional to the size of the refractory particles and inclusions, and the same result applies to the surface tension. Controlling the inclusions at a smaller size has a specific effect on alleviating the erosion of refractories. Combined with the erosion mechanism of Al₂O₃–MgO refractories, the interface reaction mechanism between Al₂O₃–MgO refractories and molten steel was proposed, which provides ideas for solving SEN clogging.
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  Effect of stress-relief annealing on thermal fatigue cracks for die-casting die steels

  Zhi-xiong Bai, Xiao-chun Wu

  钢铁研究学报(英文版). 2024, 31(5): 1164-1176.
  https://doi.org/10.1007/s42243-023-01138-6

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  The effect of stress-relief annealing at different stages of thermal fatigue tests on crack growth was investigated using a self-built thermal cycle setup. The results showed that annealing could limit crack expansion effectively. It reduced dislocation density and released the accumulation of residual stress. In addition, the strain accumulation in carbides was reduced by this process. It was also found that double annealing was even more effective at inhibiting crack expansion compared to single stress-relief annealing. After 1000 cycles, the maximum crack length was reduced by 31.1% and 45.2% for the samples after using the optimal single and double annealing processes, respectively. For single stress-relief annealing, earlier annealing provides more benefit in delaying crack expansion. However, effective double stress-relief annealing requires a suitable time interval between the annealing steps. Besides, after 800 cycles, surface hardness decreased significantly accompanied by an increase in the size and number of carbides, and cracks expanded predominantly along grain boundaries.
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  Intelligent representation method of image flatness for cold rolled strip

  Yang-huan Xu, Dong-cheng Wang, Hong-min Liu, Bo-wei Duan

  钢铁研究学报(英文版). 2024, 31(5): 1177-1195.
  https://doi.org/10.1007/s42243-023-01068-3

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  Real flatness images are the bases for flatness detection based on machine vision of cold rolled strip. The characteristics of a real flatness image are analyzed, and a lightweight strip location detection (SLD) model with deep semantic segmentation networks is established. The interference areas in the real flatness image can be eliminated by the SLD model, and valid information can be retained. On this basis, the concept of image flatness is proposed for the first time. An image flatness representation (IFAR) model is established on the basis of an autoencoder with a new structure. The optimal structure of the bottleneck layer is 16 × 16 × 4, and the IFAR model exhibits a good representation effect. Moreover, interpretability analysis of the representation factors is carried out, and the difference and physical meaning of the representation factors for image flatness with different categories are analyzed. Image flatness with new defect morphologies (bilateral quarter waves and large middle waves) that are not present in the original dataset are generated by modifying the representation factors of the no wave image. Lastly, the SLD and IFAR models are used to detect and represent all the real flatness images on the test set. The average processing time for a single image is 11.42 ms, which is suitable for industrial applications. The research results provide effective methods and ideas for intelligent flatness detection technology based on machine vision.
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  Fracture mechanism of inclusions in thick plate center under tensile loading

  Lei Hu, Li-qin Zhang, Feng Hu, Guo-hong Zhang, Kuan Zheng

  钢铁研究学报(英文版). 2024, 31(5): 1196-1209.
  https://doi.org/10.1007/s42243-023-01064-7

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  Segregation of solute atoms in the center of thick plates of the tempered steel can cause an inhomogeneous structural transformation and generate micron-sized inclusions, which leads to lamellar tearing of thick plate and decreases the plasticity and toughness. The formation and fragmentation mechanisms of micron-sized inclusions, like MnS and (Nb, Ti)C, in the center of thick plates were investigated by using thermodynamic calculations, finite element simulations, and electron backscatter diffraction characterization techniques. The results show that micron-sized inclusions nucleate and grow in the liquid phase, and under tensile loading, they exhibit three fragmentation mechanisms. The local stress during the fragmentation of inclusions is lower than the critical fracture stress of adjacent grains, and phase boundaries can effectively impede crack propagation into the matrix. The existence of a low proportion of high-angle grain boundaries (58.1%) and high Kernel average misorientation value (0.534° ) in the segregation band promotes inclusions fragmentation and crack propagation. The difference in crack initiation and propagation direction caused by the morphology of inclusions and physical properties, as well as different matrix arrest abilities, is the main reasons for the diversity of inclusion fragmentation.
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  Effect of oxide inclusions on MnS precipitates and tensile mechanical property of high-strength low-alloy steel

  Xiao-yong Gao, Hong Wei, Li-feng Zhang

  钢铁研究学报(英文版). 2024, 31(5): 1210-1220.
  https://doi.org/10.1007/s42243-023-01131-z

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  The key role of oxide inclusions on the microstructure and mechanical property of a high-strength low-alloy steel was investigated. The field emission scanning electron microscope equipped with energy-dispersive spectrometry was used to characterize MnS precipitates. Oxide inclusions play an important role in the shape control of MnS precipitates. More oxides fovored to decrease the size and the aspect ratio of MnS precipitates. With less oxide inclusions in the steel, approximately over 16.7% MnS precipitates were with aspect ratio a>5 and pure MnS precipitates accounted for 75.9% in number. However, with more oxide inclusions in the steel, only 7.4% MnS precipitates were with a>5 and pure MnS precipitates accounted for 60.1% in number. Refinement of MnS by oxide inclusions improved the strength and inhibited the anisotropy. More oxide inclusions in the steel increased the yield strength and tensile strength of the steel in both longitudinal and transverse directions, and lowered the anisotropy of the mechanical property.
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  Evolution of MnO–SiO2–Al2O3–MgO inclusions during heat treatment at 1100 C

  Xu-bo Lei, Jian-li Li, Qiang Zeng, Hang-yu Zhu, Yue Yu

  钢铁研究学报(英文版). 2024, 31(5): 1221-1231.
  https://doi.org/10.1007/s42243-023-01157-3

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  To investigate the evolutionary behavior of the MnO–SiO₂–Al₂O₃–MgO inclusions during heat treatment, water quenched samples were isothermally held at 1100 C for 120 min in Ar and air atmosphere, and the obtaining samples were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer. It showed that 3MnO Al₂O₃ 3SiO₂ and MnO SiO₂ were detected in the 5 wt.% MgO system after isothermal holding in Ar atmosphere, while MgO ・Al₂O₃, MnO・SiO₂ and Mn₇O₈・SiO₄ were detected in air atmosphere. The evolutionary behavior of the 10, 15 and 20 wt.% MgO systems after isothermal holding in different atmosphere were consistent. Oxygen affected the solid phase transformation of the low MgO content systems. The calculation results of FactSage 8.1 showed that MgO・Al₂O₃ was formed in the 5 wt.% MgO system with air atmosphere. The solid phase transformation was accompanied by grain coarsening during the isothermal holding process. The differences in the solid phase transformation in different atmosphere of the 5 wt.% MgO system indicated that it was a gas-phase transport grain coarsening mechanism. The enrichment of Al element in the liquid phase region at the grain edges, the homogeneous distribution of Mg element and the disappearance of the liquid phase within the crystal revealed that other MgO content systems were liquid–solid transport grain coarsening mechanism.
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  Synergistic effects of multiscale TiC and dual-phase structure on tensile properties of particle-reinforced steel

  Ye Jia, Xiang-tao Deng, Qi Wang, Cheng-ru Li, Hao Wu, Zhao-dong Wang

  钢铁研究学报(英文版). 2024, 31(5): 1232-1245.
  https://doi.org/10.1007/s42243-023-01110-4

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  The conventional melting methods were used to obtain in situ TiC particle-reinforced dual-phase steel, followed by hot rolling and heat treatment processes. The aim was to investigate the effect of TiC particles on the fracture behavior of dualphase steel at different annealing temperatures, by analyzing the microstructure and tensile behavior of the multiscale TiC particle-reinforced dual-phase steel. The results showed that TiC particles precipitated in the as-cast microstructure of dualphase steel were distributed along the grain boundaries. During hot rolling, the grain boundary-like morphology of the micron-sized TiC particles was disrupted, and the particles became more refined and evenly distributed in the matrix. The tensile tests revealed that the strength of the TiC particle-reinforced dual-phase steel increased with increasing martensite content, while the elongation decreased. These results were similar to those of conventional steel. The addition of 1 vol.% multiscale TiC particles improved the strength of the dual-phase steel but did not affect elongation of the steel. Cracks and holes were primarily concentrated around the TiC particles rather than at the interface of martensite and ferrite. The main causes of crack sprouting were TiC particle interface cracking and TiC particle internal fragmentation. Overall, the study demonstrated the potential of multiscale TiC particle-reinforced dual-phase steel as a strong and tough material. The refined distribution of TiC particles in the matrix improved the strength of the material without compromising its elongation. The results also highlighted the importance of careful selection of reinforcement particles to avoid detrimental effects on the fracture behavior of the material.
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  Effect of heat treatment on microstructural evolution, mechanical properties and tribological properties of H13 steel prepared using selective laser melting

  Li-xiong Han, Yan Wang, Shi-feng Liu, Zhao-hui Zhang, Wei Liu, Xin Yang, Dang-shen Ma, Jian Zhou, Ying-kang Wei

  钢铁研究学报(英文版). 2024, 31(5): 1246-1259.
  https://doi.org/10.1007/s42243-023-01065-6

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  H13 tool steel was successfully prepared by selective laser melting (SLM) technology. The effects of heat treatment on the microstructure, mechanical properties, and tribological properties of SLMed H13 steel were investigated. The heat treatment process involved a solution treatment and a double aging treatment of the deposited H13 tool steel prepared bySLM.The aim is to optimize the microstructure and mechanical properties of SLMed H13 steel. Due to the rapid heating and cooling effects of SLM, carbide precipitation in the deposited H13 steel was not uniform and residual stresses were present. The purpose of the solution treatment is to dissolve the solution at a high temperature to eliminate the residual stresses and defects introduced by the SLM-forming structure. The solution treatment and first aging treatment produced the precipitation of small carbides at the grain boundaries and inside the crystals, which increased the hardness of SLMed H13 steel. The hardness increased from 538 ± 4.0 HV of the as-deposited sample to 548 ± 5.8 HV of samples after the first aging treatment. Accordingly, the ultimate tensile strength and the elongation at break decreased from 1882 MPa and 11.5% in the as-deposited sample to 1697 MPa and 7.9% in those after the first aging treatment, respectively. Furthermore, the friction coefficient and wear rate in the as-deposited sample decreased from 0.5160 and 2.36 × 10^–6 mm^-3 N^-1 m^-1 to 0.4244 and 1.04 × 10–6 mm^-3 N^-1 m^-1, respectively. However, the distribution of carbides inside the crystals was not uniform. The second aging treatment adjusted the morphology of carbide precipitation and made it more uniform, but the precipitation of carbides grew and settled at the bottom of the grain boundaries. The hardness decreased to 533 ± 6.7 HV compared with that with the first aging treatment, but the ultimate tensile strength and plasticity reached a balance (1807 MPa, 14.05%). Accordingly, the friction coefficient and wear rate also showed a stable and decreasing trend (0.4407, 0.98 9 10–6 mm-3 N-1 m-1).
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  Multi-performance evaluation of high-throughput accelerated corrosion test for high-strength low-alloy 921A steel

  Cong-cong Du, Ming-hua Qin, Zhan-fang Wu, Dong-ling Li, Lei Zhao, Xiang-yang Li, Hai-zhou Wang,

  钢铁研究学报(英文版). 2024, 31(5): 1260-1278.
  https://doi.org/10.1007/s42243-023-01058-5

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  The corrosion behavior of high-strength low-alloy 921A steel in a simulated marine atmospheric environment was studied using a high-throughput experimental method. The corrosion behavior, corrosion morphology, and corrosion products of 921A steels were analyzed using various techniques, including corrosion mass loss method, polarization curve, white-light interferometry, scanning electron microscopy, energy-dispersive spectrometry, microbeam X-ray fluorescence spectrometry, X-ray diffraction technique, and X-ray photoelectron spectroscopy. The test results indicated that 921A steel exhibits better corrosion resistance than Q450NQR1 steel in simulated harsh atmospheric environments, as evidenced by a lower corrosion mass loss rate throughout the corrosion tests. The corrosion products of both steels consisted of α-FeOOH, Fe₃O₄, and γ-FeOOH, with α-FeOOH being more prevalent in the rust layer of 921A steel than in Q450NQR1 steel. The inner rust layer of 921A steel also exhibited an appositional enrichment region of Cr, Ni, Mo, and V, leading to its superior corrosion resistance compared to that of Q450NQR1 steel. The efficacy of high-throughput accelerated corrosion experimental methods was highlighted for evaluating the corrosion resistance of steel materials in harsh environmental conditions. The findings suggest that 921A steel exhibits better corrosion resistance compared to Q450NQR1 steel and has the potential to be more suitable in harsh marine atmospheric environments. The characterization of the rust layer structures and composition reveals the parallel enrichment of certain elements in the inner rust layer of 921A steel, which enhances its corrosion resistance.
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  Effects of two silicone resin coatings on performance of FeSiAl magnetic powder cores

  Jia-qi Liu, Zheng-qu Zhu, Pu Wang, Yi-fan Li, Jing Pang, Jia-quan Zhang

  钢铁研究学报(英文版). 2024, 31(5): 1279-1288.
  https://doi.org/10.1007/s42243-023-01105-1

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  Two silicon resins with excellent thermal stability, JH1123 and JH7102, are used as the insulated agents and binders for the gas-atomized FeSiAl powder, and corresponding magnetic powder cores (MPCs) are fabricated. The insulation capability and application prospects of the two silicon resins are evaluated by comparing the magnetic properties of the coated powder and MPCs. The scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy results show that uniform insulation layers are both formed on the powder surfaces. JH1123 has stronger binding ability, and the JH1123-coated powder exhibits severe agglomeration, with d₅₀ (average particle size) approximately twice that of the JH7102-coated powder. Both as-prepared MPCs exhibit outstanding soft magnetic properties. Wherein, the permeability of FeSiAl@JH1123 is up to 74.0, which is 35.5% higher than that of FeSiAl@JH7102 because JH1123 can further improve the density of the MPCs. As for FeSiAl@JH7102, it has better direct current bias and lower core loss of 716.9 mW cm^-3 at 20 mT and 1000 kHz due to its lower coercivity and greater antimagnetic saturation ability. A comprehensive comparison shows that FeSiAl@JH1123 is suitable for medium and high frequency applications, while FeSiAl@JH7102 is more suitable for high frequency applications. This indicates that the use of JH1123 and JH7102 silicon resins for binding and insulated coating not only simplifies the preparation process of MPCs, but also enables the controlled production of MPCs for different applications.