2024年, 第31卷, 第12期　刊出日期：2024-12-25

  

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  Roadmap, current situation, and prospects of low-carbon development technologies in Chinese steel industry

  Hai-feng Wang, Jian Qiu, Xiao-dong Ping, Feng Wang, Li-jin Lu, Ji-cheng Zhou, Xiu-ping Li

  钢铁研究学报（英文版）. 2024, 31(12): 2879-2892.
  https://doi.org/10.1007/s42243-024-01359-3

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  Carbon dioxide (CO₂) emissions have become an important factor limiting the high-quality development of the Chinese steel industry. To achieve the goal of carbon peak and carbon neutrality, the strategic planning and technological layout of low-carbon development have been carried out by the Chinese steel industry and enterprises. Based on the summary and analysis of the technology roadmap of low-carbon development in the steel industry and an evaluation of the current research progress of low-carbon technologies, the prospects for the low-carbon development of the steel industry in the future were provided. The results indicate that some steel enterprises in China have already released their low-carbon development roadmaps with a focus on achieving carbon neutrality, which will be realized through advancements in system energy efficiency improvement, resource recycling, process optimization and innovation, breakthrough in smelting technology, product iteration and upgrading, and carbon capture, utilization, and storage (CCUS). The technology development of hydrogen metallurgy and CCUS has shown rapid progress. In the future, the Chinese steel industry must continue to prioritize low-carbon technology and promote the utilization of clean energy. The ratio of electric arc furnace steel should be increased gradually, and the development and application of CCUS technology should be promoted, to ensure the achievement of the “carbon peak and carbon neutrality” goal.
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  Effect of silica on crystallization process of calcium ferrite: thermodynamic and kinetic analysis

  Xu-chao Wang, Cheng-yi Ding, Xue-wei Lv, Hong-ming Long, Yu-xi Wu, Feng Jiang, Ren-de Chang, Sheng Xue, Qing-lin Chen

  钢铁研究学报（英文版）. 2024, 31(12): 2893-2902.
  https://doi.org/10.1007/s42243-024-01242-1

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  SiO₂ is the main component of gangue in sinters and a crucial constituent in the formation of the SiO₂-Fe₂O₃-CaO (SFC) system. The non-isothermal crystallization kinetics of the SFC system were investigated using differential scanning calorimetry. The crystallization process of SFC was studied under different cooling rates (5, 10, 15, and 20 K/min), and the crystalline phases and microstructures of the SFC crystals were verified through X-ray diffraction and scanning electron microscopy. The results indicate that when the SiO₂ content is 2 wt.%, increasing the cooling rate promotes the precipitation of CaFe₂O₄ (CF) in the SFC system, thereby inhibiting the precipitation of Ca₂Fe₂O₅ (C2F). In contrast to the CaO- Fe₂O₃ (C-F) system, the addition of SiO₂ does not alter the precipitation mechanisms of C₂F and CF. By further adding SiO₂, the precipitation of Ca₂SiO₄ (C₂S) significantly increases. Simultaneously, the CaO content in the liquid phase decreases. This leads to the crystallization process of the CF₄S (4 wt.% SiO₂) system bypassing the precipitation of C₂F and directly forming CF and CaFe₄O₇ (CF₂). In the case of the CF₈S (8 wt.% SiO₂) system, the crystallization process skips the precipitation of C₂F and CF, directly yielding CF₂. The crystallization process of both CF₂S (2 wt.% SiO₂) and CF is similar, comprising two reaction stages. The Ozawa method was used to calculate the activation energy for the crystallization of C₂F and CF as — 329 and — 419 kJ/mol, respectively. Analysis using the Malek method reveals model functions for both stages.
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  A new insight into iron ore oxidized pellets prepared by steel belt roasting process

  Tao Jing, Hao Lv, Min Gan, Xiao-hui Fan, Jing Li, You-xun Dai, Zhuo-qi Liu, Shi-xian Li

  钢铁研究学报（英文版）. 2024, 31(12): 2903-2914.
  https://doi.org/10.1007/s42243-024-01336-w

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  The steel belt roasting process has the advantages of low cost, small footprint, and high thermal efficiency, making it widely used in the smelting of ferroalloys such as ferrochrome, ferromanganese, and ferroniobium. However, its application in preparing iron ore oxidized pellets has not been sufficiently explored. The optimal thermal process conditions for magnesium-containing oxidized pellet preparation by steel belt roasting machine were investigated based on the roasting properties of high-magnesium iron concentrate and typical iron concentrate. The results indicate that, for the blending scheme of 70 wt.% high-magnesium iron concentrate and 30 wt.% typical iron concentrate, the appropriate preheating temperature for pellets is 950-975 °C and the suitable roasting temperature is 1250-1275 °C, during which the compressive strength of pellets can exceed 2500 N pellet^-1. During the steel belt roasting process, SO₂ is primarily released in the preheating zone, and the maximum exhaust gas temperature in the roasting zone can reach 637 °C. High-temperature sulfur-containing exhaust gas causes oxidation corrosion, sulfide corrosion, and deformation of the steel belt. To enhance the steel belt longevity, it is recommended to appropriately reduce the wind velocity in the preheating zone and roasting zone, while also decreasing the ratio of pellet bed height to hearth layer height. By adopting the system of “low wind velocity, thin pellet bed, fast steel belt speed,” the exhaust gas temperature can be reduced to 463 °C. The prepared pellet maintains a compressive strength of 2607 N pellet^-1 and exhibits excellent metallurgical properties.
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  Denitrification characteristics and reaction mechanism of Ce-doped Fe- based catalysts from modified metallurgical dust containing iron

  Zhi-fang Gao, Hong-ming Long, Xiang-peng Gao, Hao Zhang

  钢铁研究学报（英文版）. 2024, 31(12): 2915-2926.
  https://doi.org/10.1007/s42243-024-01293-4

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  Metallurgical dust (MD) was used as raw material to prepare rare earth Ce-doped Fe-based catalysts. The results show that the Ce_0.1/AMD-300 °C catalyst prepared from acid-modified diatomite (AMD) with m_Ce/m_MD = 0.1 (m_Ce and m_MD are the mass of Ce and MD, respectively) after being roasted at 300 °C can reach 99% NO_X removal rate in the wide temperature range of 230-430 °C and exhibits excellent SO₂ and H₂O resistance. The MD effectively removes alkali metal elements by the modification process, increases the specific surface area and optimizes the pore structure of MD. The doping of Ce element makes Fe-based catalysts have more surface adsorbed oxygen O_α and a higher Ce³⁺/Ce⁴⁺ ratio. Through ammonia temperature-programmed desorption and hydrogen temperature-programmed reduction, it was found that the strong interaction between cerium and iron promotes the formation of more oxygen cavities in the catalyst, thereby generating more active and easily reducible oxygen species and promoting the transformation of Brønsted acid site to Lewis acid site. The research results provide a theoretical basis for the preparation of efficient and inexpensive Fe-based catalysts from MD.
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  Effect of carbon concentration on melting behavior of steel scraps in hot metal baths

  Wei Liu, Cheng-song Liu, Cheng-jie Song, Yong Wang, Wan-jun Zhu, Hua Zhang, Hong-wei Ni

  钢铁研究学报（英文版）. 2024, 31(12): 2927-2939.
  https://doi.org/10.1007/s42243-024-01273-8

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  To reveal the intricate mechanisms underlying the melting and dissolution processes of scraps in the iron ladle, the melting characteristics of three carbon steels with different C concentrations at the bath temperatures of 1623 and 1723 K were studied. Upon immersing scraps into the molten metal, the liquid metal immediately froze around the submerged parts of scrap cylinders. Whereafter, the solid shell completely melted at both bath temperatures after the immersion time of 5 s. The maximum thickness of solidified steel shells significantly decreased with increasing the bath temperature. The findings also suggested that the melting rate of scrap cylinder exhibited a positive correlation with the C concentration in the scrap and the bath temperature. Quantitatively, the mass transfer coefficients of C for the low carbon (0.18 wt.%), medium carbon (0.32 wt.%), and high carbon (0.61 wt.%) concentrations in the scrap cylinders at 1723 K were determined by a kinetic model, which were 8.78×10^-5, 9.57×10^-5 and 10.00×10^-5 m s^-1, respectively, and those corresponding values decreased to 3.87×10^-5, 4.49×10^-5 and 3.54×10^-5ms^-1at 1623 K. However, there was little difference observed among the heat transfer coefficients of hot metal for the three carbon steels, which were estimated to have an average value of 16.36 and 18.82 kW m^-2 K^-1 at the experimental temperatures of 1623 and 1723 K, respectively. The results from the experiments and mathematical models showed good consistency at both bath temperatures, providing feasible guidance for efficient melting of steel scraps in the iron ladle.
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  Application of XGBoost and kernel principal component analysis to forecast oxygen content in ESR

  Yu-xiao Liu, Yan-wu Dong, Zhou-hua Jiang, Qi Wang, Yu-shuo Li

  钢铁研究学报（英文版）. 2024, 31(12): 2940-2952.
  https://doi.org/10.1007/s42243-024-01205-6

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  A model combining kernel principal component analysis (KPCA) and Xtreme Gradient Boosting (XGBoost) was introduced for forecasting the final oxygen content of electroslag remelting. KPCA was employed to reduce the dimensionality of the factors influencing the endpoint oxygen content and to eliminate any existing correlations among these factors. The resulting principal components were then utilized as input variables for the XGBoost prediction model. The KPCA- XGBoost model was trained and proven using data obtained from companies. The model structure was adapted, and hyperparameters were optimized using grid search cross-validation. The model performance of the KPCA-XGBoost model is compared with five machine learning models, including the support vector regression model. The findings demonstrated that the KPCA-XGBoost model exhibited the highest level of prediction accuracy, indicating that the incorporation of KPCA significantly enhanced the regression prediction performance of the model. The accuracy of the KPCA-XGBoost model was 82.4%, 97.1%, and 100% at errors of ±1.5 x 10^-6, ±2.0 x 10^-6, and ±3 x 10^-6 for oxygen content, respectively.
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  Influence of silica fume on drying shrinkage of alkali-activated carbon steel slag

  Jin-yan Liu, Xiao-tong Deng, Qiang Ren, Sen Liu, Zhi-bin Ma

  钢铁研究学报（英文版）. 2024, 31(12): 2953-2970.
  https://doi.org/10.1007/s42243-024-01325-z

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  Drying shrinkage is an important factor affecting the durability of alkali-activated materials. The drying shrinkage of alkali-activated carbon steel slag and the effect of silica fume substitution were studied. The drying shrinkage test lasted for 300 d. The compressive strength, flexural strength, Vickers hardness, mass recovery and drying shrinkage recovery of the samples after drying shrinkage were tested. The hydration products and microstructure were characterized by X-ray diffraction, mercury intrusion porosimetry, thermogravimetry-differential thermogravimetry, and scanning electron microscopy-energy dispersive spectroscopy. The results show that although the chemical expansion compensates for the drying shrinkage in 42 d, the drying shrinkage increases continuously within 300 d. Silica fume affects drying shrinkage by refining pore size and increasing matrix microhardness. Solid surface tension and capillary pressure are the driving forces for drying shrinkage in the early and middle to late stages, respectively. The evolution of drying shrinkage is also influenced by chemical expansion, matrix microhardness and macropore collapse.
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  Statistical study of mechanical responses of ordinary refractory ceramics under cold crushing condition with discrete element modeling

  Wei-liang Du, Sheng-li Jin

  钢铁研究学报（英文版）. 2024, 31(12): 2971-2980.
  https://doi.org/10.1007/s42243-024-01344-w

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  Ordinary refractory ceramics are multi-phase materials, and their inhomogeneous microstructures induce the scatter of properties. The definition of a reasonable number of samples is important to obtain representative results from experiments and simulations, and this reasonable number might be property or microstructure relevant. Stochastic discrete element (DE) simulations of cold crushing tests with homogeneous interface properties were performed. Three minimum DE size ranges were used to represent matrix variation at different levels. Statistical methods, i.e., Kolmogorov-Smirnov (K-S) test, t-test, and correlation analysis, were utilized to study the influences of minimal number of samples on mechanical properties and crack density. It revealed that a relatively small number of samples are sufficient to obtain representative cold crushing strength (CCS) and Young's modulus, whilst a large number of samples are favourable when the fracture energy and crack density under cold crushing conditions are of interest. The analysis also showed that the fracture energy under cold crushing condition generally correlates positively with CCS, and the static Young's moduli determined from the stress- piston displacement curves with different definitions are divergent, caused by contact compliance and premature cracking. The data from the stress-strain curves recorded directly on the sample are required for the accurate static Young's modulus calculation.
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  Improvement on central porosity of large-sized round bloom by solidification end reduction during continuous casting

  Peng Lan, Liang Li, Jia-quan Zhang

  钢铁研究学报（英文版）. 2024, 31(12): 2981-2996.
  https://doi.org/10.1007/s42243-024-01362-8

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  A three-dimensional finite element model coupled with heat transfer, shrinkage accumulation and high temperature deformation was established for ø690 mm round bloom in continuous casting, and it was verified by surface temperature, shell thickness, contour shape and porosity size by measurement. The compensation area of the shrinkage zone increases as the reduction amount increases. The compensation effect by the reduction of the unit with liquid core is about two times higher than others with fully solid matrix at a given reduction amount. A mathematical method to determine the reduction parameters for large-sized round bloom during continuous casting was proposed by the multi-rollers strategy. For the ø690 mm round bloom, the suitable reduction parameters for Nos. 2-6 units are suggested as 15, 15, 10, 10, 10 mm with a casting speed of 0.26 m min^-1 to close the shrinkage with a diameter of about 17.5 mm in average. The industrial test on the reduction of large-sized round bloom for LZ50 steel was carried out. A total amount of 65-70 mm reduction was realized in the bloom for different casting speeds. The maximum diameter of the central porosity is about 16.3 mm in the longitudinal section at the casting speed of 0.24 m min^-1, and it decreases to 7.3 mm after 65 mm reduction. Meanwhile, the maximum diameter of the central porosity is about 18.7 mm at 0.26 m min^-1, while it decreases to 4.1 mm by a reduction of 70 mm. Finally, the difference of the solidification end reduction on round bloom and rectangular or square bloom is theoretically compared. Low deformation resistance and high bulge effect were found in round bloom compared to rectangular bloom. According to the results about solidification contraction accumulation and reduction efficiency in round bloom, the suitable reduction zone to control the central porosity during continuous casting is suggested to be 0.5-1.0.
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  Effect of heating temperature on microstructure and properties of Ti/steel clad plates with corrugated interfaces

  Ping-ju Hao, Yuan-ming Liu, Yi-yang Zhang, Tao Wang, Qing-xue Huang, Zhen-guo Wang

  钢铁研究学报（英文版）. 2024, 31(12): 2997-3006.
  https://doi.org/10.1007/s42243-024-01366-4

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  To solve the problems of severe interface oxidation at high temperature, low interface bonding strength at low temperature, and severe plate shape warping in the traditional flat rolling process for preparing Ti/steel clad plates, a new corrugated-flat rolling (CFR) process is adopted to prepare Ti/steel clad plates with corrugated interface. The study investiagtes the effects of different heating temperatures on the interface morphology, mechanical properties and corrosion resistance. Ti/steel clad plates prepared by CFR process have a distinct corrugated three-dimensional interface. The diffusion range of interface elements and the thickness of solid solution diffusion layer change with different heating temperatures. The tensile-shear strength of the clad plate increases first and then decreases with the increase in heating temperature, peaking at 327 MPa at 900 °C. The tensile strength is less affected by heating temperature, and the maximum tensile strength is achieved at a heating temperature of 800 °C, with a value of 766 MPa. During the fracture process of the clad plates, the steel exhibits plastic fracture characteristics, while Ti exhibits a mixture of plastic and brittle fracture characteristics. The overall corrosion resistance of Ti surface in the clad plate is good. As the heating temperature increases, the polarization resistance of Ti surface decreases, the current density in the passivation zone increases, and the active sites and energy required for the formation of the passivation film decrease.
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  Inclusion characteristics and acicular ferrite formation in 1.8%Nilow carbon Al-killed steel with MgO nanoparticles addition

  Meng Sun, Yang Li, Zhou-hua Jiang, Shuai Ma, Yong-shuai Ji, Yun-qie Mao, Chang-yong Chen, Yu-cheng Wang, Rui Yang

  钢铁研究学报（英文版）. 2024, 31(12): 3007-3021.
  https://doi.org/10.1007/s42243-024-01240-3

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  The effect of adding MgO nanoparticles (0%, 0.01%, 0.05%, and 0.10%) on the inclusion and acicular ferrite (AF) formation in 1.8%Ni low carbon Al-killed (LCAK) steel was explored. The inclusion analysis reveals that MgO nanoparticles react with dissolved Al or Al₂O₃ inclusions and finally change to fine MgAl₂O₄ wrapped by MnS in the case of adding 0.05% MgO nanoparticles. In contrast, MgO nanoparticles are agglomerated and form Mg-bearing inclusion clusters in the case of 0.10% or reduced to high Al₂O₃ inclusions by dissolved Al in the case of 0.10%. The microstructure observations show that the AF formation was promoted in the case with addition of 0.05% MgO nanoparticles. The process of inclusion-inducing AF nucleation is essentially characterized via the high-temperature confocal scanning laser microscopy experiment. dmin (d denotes disregistry) of Al₂O₃/α-Fe, MgAl₂O₄/α-Fe, and MnS/α-Fe is evaluated to be 11.5%, 6.5%, and 7.4%, respectively. The high AF fraction in the case of 0.05% MgO addition can be attributed to the low disregistry of MnS-MgALOVferrite and Mn-depleted zone adjacent to the MnS layer. Based on the results, 0.05% was recommended as the proper addition amount of MgO nanoparticles in 1.8%Ni LCAK steel.
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  Revealing dislocation activity modes during yielding and uniform deformation of low-temperature tempered steel by acoustic emission

  Jie Li, Jia-zhi Zhang, Li-yang Zeng, Shuai Wang, Xiang-yu Song, Nai-lu Chen, Xun-wei Zuo, Yong-hua Rong

  钢铁研究学报（英文版）. 2024, 31(12): 3022-3036.
  https://doi.org/10.1007/s42243-024-01253-y

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  The distinctive distribution of acoustic emission (AE) characteristic parameters generated during tensile testing of low- temperature tempered AISI4140 steel was investigated. Two clusters of acoustic emission signals were distinguished using power-law distribution fitting and k-means clustering methods. These clusters were identified as resulting from dislocation motion during yielding and dislocation entanglement during uniform plastic deformation. The conclusion is further confirmed by transmission electron microscopy images at different strains. In particular, the unique “arch-shaped⁵⁵ distribution of the acoustic emission energy during yielding implies a change in unusual dislocation motion modes. The effect of carbide precipitation was qualitatively discussed as not considering the primary cause of the formation of this archshaped distribution. The evolution of dislocation motion modes during yielding of low-temperature tempered martensite was elucidated by comparing the significant difference in cumulative energy values during yielding of annealed and low- temperature tempered specimens. Dislocations emit from Frank-Read or grain boundary sources and slip along short free paths, contributing to the initial increase in AE signals energy. Subsequently, the primary source of acoustic emission energy “arch-shaped” peak during yielding was generated by the avalanche behavior of accumulated dislocations, leading to the accelerated dislocation motion.
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  Effect of electric current on secondary phase dissolution and elements migration behavior of a Ni-based single crystal superalloy

  Ying-ju Li, Ce Zheng, Xiao-hui Feng, Qiu-yan Huang, Tian-jiao Luo, Yuan-sheng Yang

  钢铁研究学报（英文版）. 2024, 31(12): 3037-3047.
  https://doi.org/10.1007/s42243-024-01266-7

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  The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution heat treatment of the Ni- based single crystal superalloy. The results showed that the electric current solution heat treatment improved microstructural homogenization as well as the distribution of alloying elements, especially for the refractory metal W and Mo. The microsegregation ratios for Mo and W after electric current solution heat treatment at 1230 °C for 4 h are near those without electric current at 1250 °C for 4 h. The electric current accelerated the y⁰ phase dissolution process, and the c' phase could be completely dissolved at a lower treatment temperature or within a shorter treatment time under electric current solution heat treatment with direct current. A microcosmic current model was proposed to analyze the effect of the electric current on the solution heat treatment of the Ni-based single crystal superalloy.
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  Preparation of Si₃N₄-TiN-SiC composite by partial substitution of Ti-Si-Fe alloy for Si under N₂ atmosphere

  Lu-yan Yao, Jin-hua Zhang, Bing-qiang Han, Yue-e Ni, Chang-ming Ke

  钢铁研究学报（英文版）. 2024, 31(12): 3048-3057.
  https://doi.org/10.1007/s42243-024-01196-4

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  Si₃N₄-TiN-SiC composites were prepared by partial substitution of the Ti-Si-Fe alloy extracted from high-titanium blast frnace slag for Si under nitrogen atmosphere. The nitridation, microstructure and mechanical properties of the composites were investigated in detail. The results show that Ti-Si-Fe alloy facilitated the nitridation of Si and full nitridation of Si was achieved in the compacts with 3.6-5.4 wt.% Ti-Si-Fe alloy additive, and thus, densification and mechanical performances of the composites were improved obviously. Propagating of microcracks induced by the volume expansions accompanying with the conversion of Ti₅Si₃ and TiSi₂ to nitrides at 950-1050 °C built new N₂(g) transport channels in the compacts. In the following up nitridation process, adequate N₂(g) was transported through these channels into the compacts to fundamentally enhance contact of N₂ with Si, facilitate and ensure the complete nitridation of internal Si. Moreover, the Ti-Si-Fe-Mn-N eutectic liquid played an important role in the formation of bothα- and p-Si₃N₄, and the Fe in the Ti-Si- Fe alloy was of great importance for the formation of fibrous Si₃N₄ by the reaction between SiO(g) and N₂(g)
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  Compositional correlations to intrinsic magnetic properties in binary and Ti-alloyed MnAl magnetic alloys

  Shuang Zhao, Ying Dong, Yu-xiao Jia, Yi-chen Xu, Yu-ye Wu

  钢铁研究学报（英文版）. 2024, 31(12): 3058-3068.
  https://doi.org/10.1007/s42243-024-01239-w

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  MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives, which have attracted extensive attentions in recent decades. We reported the evolution in phase formation and intrinsic magnetic properties of τ-phase in binary MnAl alloys with the variation in Mn:Al ratios. Ferromagnetic τ-phase can be generated within the compositional range of Mn_50+xAl_50-x (x = 1-8), and pure τ-phase can only be obtained in the alloys with x = 4-7. With Mn:Al ratio increasing, saturation magnetization M_s and magnetocrystalline anisotropy constant K₁ are gradually weakened due to the incremental antiferromagnetic Mn-1d atoms, but Curie temperature of τ-phase is gradually increased induced by the strengthened d-d hybridization of Mn_1a-Mn_1d. An attempt of doping traces of Ti was carried out in order to eliminate the negative antiferromagnetic interaction derived from Mn-1d atom. Ti atoms tend to occupy 1d sites and replace the Mn-1d atoms due to the relatively fewer valence electrons compared with Mn, resulting in the reduction in Mn_1a-Mn_1d antiferromagnetic interactions, which is demonstrated by the higher M_s of Mn_55-yAl₄₅Ti_y(y=1) than that of Mn₅₅Al₄₅. However, with further substitution of Mn by Ti, unfavorable κ-phase is unavoidably generated. Finally, the occupation preference and the corresponding influences on local magnetic interactions as well as the magnetizations of the different alloying atoms including interstitial element C, 3d atoms Ti, Co and Cu, and main-group element Ga are systematically summarized, in order to offer the guidance of designing MnAl permanent magnets with ideal magnetic properties.
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  Effect of distance between heat sources on droplet transfer behavior and weld formation of AH36 during laser and CWW GMAW arc hybrid welding

  Yun-tao Chen, Zhi-dong Yang, Zheng-xuan Ni, Jiang-min Xu, Shan-wen Dong, Guo-xiang Xu, Shu-jin Chen

  钢铁研究学报（英文版）. 2024, 31(12): 3069-3079.
  https://doi.org/10.1007/s42243-024-01224-3

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  In order to analyze the influence of the distance between heat sources (D_LA) On the welding process, the effects of D_LA On the droplet transfer behavior, weld formation characteristics and weld formation mechanism of AH36 in laser and cable- type welding wire gas metal arc welding arc hybrid welding were studied. Real-time photography was conducted using a high-speed camera to determine the droplet transfer and arc behaviors; the surface morphology and macroscopic crosssection of the weld obtained from the experiment were observed and analyzed. The arc height decreases with the increase in the D_LA, the arc width shows the opposite change, and the welding current decreases. The allure of the laser to the arc increases with the increase in the D_LA. The frequency of droplet transfer increases with the increase in the D_LA, but the growth rate decreases. The continuous increase in the D_LA leads to the tendency of the droplet size to decrease first and then increase, and the minimum value is obtained when the D_LA is 4 mm. The D_LA has obvious influence on the weld formation. The weld penetration and reinforcement change similarly, increasing first and then decreasing as the D_LA increases, and the laser area of the weld also increases first and then decreases.
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  Microstructural and nanomechanical behavior of friction stir welded dissimilar joint of AA2219-T6/AA2195-T8 alloys

  Di-chao Wu, Fei-fan Wang, Shen Li, Wen-qin Wang, De Wang, Yu-long Li, Tan Miao

  钢铁研究学报（英文版）. 2024, 31(12): 3080-3094.
  https://doi.org/10.1007/s42243-024-01272-9

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  To achieve the new strategy of low cost and outstanding property, friction stir welding (FSW) was used to join AA2219-T6 alloy and AA2195-T8 alloy. The relationship between macro/microstructure and nanomechanical properties was established by using a nanoindentation instrument. During FSW, the grains in stir zone were refined by recrystallization, and the main mechanism of recrystallization was continuous dynamic recrystallization and geometric dynamic recrystallization. The overall micro-hardness value of AA2195 alloy was higher than that of AA2219 alloy due to the strength of the material, and the decrease in hardness value is attributed to the dissolution and coarsening of precipitation. Each zone of the dissimilar joint showed obvious indentation size effect, and the highest nano-hardness values of 2219-base metal (BM) and 2195-BM zones were 1.42 and 1.71 GPa, respectively. The nano-hardness is closely related to the precipitation behavior and follows the same law as the distribution of micro-hardness. The creep mechanism was mainly dislocation slip. The combined action of grain boundary, dislocation, and coarse precipitation can affect creep resistance, in which coarse precipitation plays a dominant role.
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  Effect of isothermal martensite and bainite transformation on microstructure and properties in a medium-carbon high-strength Q&P steel

  Ya-jun Liu, Jun-yu Tian, Man Liu, Xiao-long Gan, Sheng Liu, Guang Xu

  钢铁研究学报（英文版）. 2024, 31(12): 3095-3108.
  https://doi.org/10.1007/s42243-024-01216-3

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  The effect of the amount of isothermal martensite and bainite on the microstructure and properties in a medium-carbon quenching and partitioning (Q&P) steel was investigated by designing the different Q&P treatment parameters. The results show that the amount of isothermal martensite increased gradually with the increase in quenching time. The increase in isothermal martensite amount improved the product of strength and elongation (PSE) of Q&P steels. In addition, the increase in carbides amount and the recovery in prior martensite with longer partitioning time led to an increase in PSE first and then, a decrease. It implies that a higher PSE could be obtained by the selection of a suitable partitioning time. Furthermore, the effect of bainite transformation during partitioning on PSE was investigated by designing the different partitioning temperatures, including 300, 400 (below bainite starting temperature, Bs) and 480 °C (above Bs). The results show that compared with the samples partitioned at temperature above Bs, the bainite transformation was only detected when the samples were partitioned at temperature below Bs. The bainite transformation amount increased with the decreasing partitioning temperature, leading to the inhibition of carbides precipitation and more stable RA and thus, resulting in the highest PSE.
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  Effect of Ta content on high temperature oxidation and hot corrosion resistance of DZ411 superalloy

  Peng Peng, Yi-fan Ma, Zi-jie Liu, Su-jun Lu, Yuan-li Xu, Xu-dong Zhang, Zhi-kun Ma

  钢铁研究学报（英文版）. 2024, 31(12): 3109-3119.
  https://doi.org/10.1007/s42243-024-01201-w

  摘要 ( ) PDF全文 ( )   可视化   收藏

  In order to elucidate the mechanism of the effect of Ta content on the high temperature behaviour of the alloys, the high temperature oxidation and thermal corrosion experiments were carried out on the three alloys with different Ta contents (2.72, 3.10 and 4.00 wt.%). The results of high temperature oxidation and hot corrosion show that because Ta has a higher valence state than Al, it can reduce the indiffusion of O, and the rate at which Ta diffuses within the alloy matrix is relatively slow since it has a larger atomic radius. As a result, the diffusion of the Al element is inhibited as the Ta content increases. Therefore, adding Ta inhibits the formation of Al₂O₃ in the surface oxide and promotes the formation of Cr₂O₃. Thus, Ta promotes oxidised film growth on the sample surface, which inhibits the diffusion of S, O and other elements into the matrix. Additionally, Cr₂O₃ is not easy to dissolve in molten salt, which ultimately makes the alloy have high oxidation resistance and thermal corrosion resistance.
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  High-temperature corrosion resistance of Fe-Cr-Mo amorphous coating for water wall protection of USC boiler

  Zhao Zhang, Cheng Zhou, Fang-zhou Jin, Yong-feng Cai, Yi-fan Ni, Cheng-hao Fan, Dan Song

  钢铁研究学报（英文版）. 2024, 31(12): 3120-3134.
  https://doi.org/10.1007/s42243-024-01237-y

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  A novel Fe-Cr-Mo amorphous coating, a high-temperature corrosion-resistant material for water wall protection of power plant ultra-supercritical boilers, has been prepared via arc spraying. A systematic study was conducted to evaluate the high- temperature corrosion behavior of this coating, and its resistance to corrosion at high temperatures was scientifically assessed. The results indicate that the thickness of Fe-Cr-Mo amorphous coating is approximately 350 im, exhibiting typical amorphous characteristics as confirmed by X-ray diffraction and transmission electron microscope characterization. During each stage of the 750 °C corrosion test, the oxygen content of the amorphous coating was significantly lower than that of the contrast coating (PS45 alloy coating), indicating a superior corrosion protection effect at high temperature. After 100 h of continuous testing, the corrosion mass gain of the amorphous coating was only 28.62% that of PS45 coating and 3.89% that of T12 steel substrate, indicating significantly depressed high-temperature corrosion kinetics. The excellent high-temperature corrosion resistance of Fe-Cr-Mo amorphous coating is primarily attributed to the stable Fe/Cr oxide film generated by the metastable state of the amorphous state, which serves as an excellent barrier. Furthermore, under the influence of heat in a high-temperature environment, the amorphous structure gradually transforms into a nanocrystalline structure. In contrast, the oxide film of the amorphous/nanocrystalline coating has low thermal stress, leading to better adhesion with the coating and resistance to cracking and peeling, thus providing excellent sustained protection.