2024年, 第31卷, 第9期　刊出日期：2024-09-25

  

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  Role of retained austenite in advanced high-strength steel: ductility and toughness

  Vung Lam Nuam, Hao Zhang, Ying-chun Wang, Zhi-ping Xiong

  钢铁研究学报（英文版）. 2024, 31(9): 2079-2089.
  https://doi.org/10.1007/s42243-023-01165-3

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  Enhancing the ductility and toughness of advanced high-strength steels is essential for the wide range of promising applications. The retained austenite (RA) is a key phase due to the austenite-to-martensite transformation and its transformation-induced plasticity effect. It is commonly accepted that slow RA-to-martensite transformation is beneficial to ductility; therefore, the RA fraction and stability should be carefully controlled. The RA stability is related to its morphology, size, carbon content, neighboring phase and orientation. Importantly, these factors are cross-influenced. It is noteworthy that the influence of RA on ductility and fracture toughness is not consistent because of their difference in stress state. There is no clear relationship between fracture toughness and tensile properties. Thus, it is important to understand the role of RA in toughness. The toughness is enhanced during the RA-to-martensite transformation, while the fracture toughness is decreased due to the formation of fresh and brittle martensite. As a result, the findings regarding to the effect of RA on fracture toughness are conflicting. Further investigations should be conducted in order to fully understand the effects of RA on ductility and fracture toughness, which can optimize the combination of ductility and toughness in AHSSs.
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  Identification of working conditions and prediction of FeO content in sintering process of iron ore fines

  Xiao-ming Li, Bao-rong Wang, Zhi-heng Yu, Xiang-dong Xing

  钢铁研究学报（英文版）. 2024, 31(9): 2090-2100.
  https://doi.org/10.1007/s42243-024-01220-7

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  The iron oxide (FeO) content had a significant impact on both the metallurgical properties of sintered ores and the economic indicators of the sintering process. Precisely predicting FeO content possessed substantial potential for enhancing the quality of sintered ore and optimizing the sintering process. A multi-model integrated prediction framework for FeO content during the iron ore sintering process was presented. By applying the affinity propagation clustering algorithm, different working conditions were efficiently classified and the support vector machine algorithm was utilized to identify these conditions. Comparison of several models under different working conditions was carried out. The regression prediction model characterized by high precision and robust stability was selected. The model was integrated into the comprehensive multi-model framework. The precision, reliability and credibility of the model were validated through actual production data, yielding an impressive accuracy of 94.57% and a minimal absolute error of 0.13 in FeO content prediction. The real-time prediction of FeO content provided excellent guidance for on-site sinter production.
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  CO₂ emission evaluation and cost analysis of oxygen blast furnace process with sintering flue gas injection

  Wei Zhang, Jia-meng Lei, Jing-qi Li, Guo-jun Ma, Henrik Saxén

  钢铁研究学报（英文版）. 2024, 31(9): 2101-2109.
  https://doi.org/10.1007/s42243-023-01141-x

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  In order to achieve ultra-low emissions of SO₂ and NO_x, the oxygen blast furnace with sintering flue gas injection is presented as a promising novel process. The CO₂ emission was examined, and a cost analysis of the process was conducted. The results show that in the cases when the top gas is not circulated (Cases 1-3), and the volume of injected sintering flue gas per ton of hot metal is below about 1250 m³ , the total CO₂ emissions decrease first and then increase as the oxygen content of the blast increases. When the volume of injected sintering flue gas per ton of hot metal exceeds approximately 1250 m³ , the total CO₂ emissions gradually decrease. When the recirculating top gas and the vacuum pressure swing adsorption are considered, the benefits of recovered gas can make the ironmaking cost close to or even lower than that of the ordinary blast furnace. Furthermore, the implementation of this approach leads to a substantial reduction in total CO₂ emissions, with reductions of 69.13% (Case 4), 70.60% (Case 5), and 71.07% (Case 6), respectively. By integrating previous research and current findings, the reasonable oxygen blast furnace with sintering flue gas injection can not only realize desulfurization and denitrification, but also achieve the goal of reducing CO₂ emissions and iron-making cost.
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  Low-temperature deNO_x performance and mechanism: a novel FeVO4/ CeO2 catalyst for iron ore sintering flue gas

  Long Ding, He-xi Zhao, Ke Cheng, Li-xin Qian, Peng-yu Qi, Qi Shi, Hong-ming Long

  钢铁研究学报（英文版）. 2024, 31(9): 2110-2121.
  https://doi.org/10.1007/542243-024-01203-8

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  Developing deNO_x catalysts with lower activity temperatures range significantly reduces NH₃ selective catalytic reduction (SCR) operating costs for low-temperature industrial flue gases. Herein, a novel FeVO₄/CeO₂ catalyst with great lowtemperature NH₃-SCR and nitrogen selectivity was synthesized using a dipping method. Characterization techniques such as X-ray diffraction, Raman spectroscopy, specific surface and porosity analysis, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption, X-ray photoelectron spectroscopy, and the in situ diffused reflectance infrared Fourier transform spectroscopy were used to investigate the catalytic mechanism. An appropriate addition for FeVO₄ in the catalyst was 5 wt.% from the results, and the active substance content reached the maximum dispersal capacity of the carrier. The NO_x conversion exceeded 90%, and the nitrogen selectivity was more than 98% over this catalyst at 200-350 ℃. The activity was kept at 88% after 7.5 h of reaction at 200 ℃ for 7.5 h in 35 mg m^-3 SO₂ gas. The remarkable deNO_x activity, nitrogen selectivity, and sulphur resistance performances are attributed to the low redox temperature, the abundance of medium-strong acid and strong acid sites, the sufficient adsorbed oxygen, and the superior Fe²⁺ content on the surface. The Langmuir-Hinshelwood mechanism was observed on the FeVO₄/CeO₂ catalyst in the NH₃ selective catalytic reduction of NO_x.
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  Effect of ferrotitanium slag on microstructure and properties of Al₂O₃-SiC-C castables for iron runner

  Tu Long, Hua-zhi Gu, Mei-jie Zhang, Ao Huang, Lv-ping Fu, Ding Chen, Wen-dong Qiu, Mao-qi Ju

  钢铁研究学报（英文版）. 2024, 31(9): 2122-2132.
  https://doi.org/10.1007/s42243-023-01169-2

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  Ferrotitanium slag (FS) is a waste slag produced during the smelting of ferrotitanium alloys by thermite reduction. Its alumina content is high and can be used as alumina raw material. Iron runner castables containing different amounts of FS were prepared and characterized. The results show that the introduction of FS is beneficial to the sintering of the castables sample. When the FS concentration is 11.2 wt.%, the aggregate and matrix of the castables sample have a good combination, and the mechanical strength of the Al₂O₃-SiC-C castable reaches a maximum at room temperature. However, excessive introduction of FS generates a large amount of anorthite phase, which reduces the mechanical strength of the Al₂O₃-SiC-C castable at room temperature. In addition, the high-melting phase CaTiO₃ is formed in FS, which has good mechanical properties. Meanwhile, the cracks of FS are reduced, and the combination between phases is closer, thus significantly improving the hot modulus of rupture of the castable. When the FS concentration is not above 33.6 wt.%, the castables show good slag resistance. The TiO₂ in FS is transformed into TiC by carbothermal reaction, which is enriched at the boundary and prevents further reaction of the slag.
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  Effect of water loss during curing on hydration reaction and hydrates conversion in calcium aluminate cement-bonded castables

  Zhong-zhuang Zhang, Xiao-yu Wang, Song-zhu Chu, Jin-yan Zeng, Yuan-dong Mu, You-qi Li, Zhong-tao Luo, Guo-tian Ye

  钢铁研究学报（英文版）. 2024, 31(9): 2133-2141.
  https://doi.org/10.1007/s42243-023-01161-7

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  Free water available in calcium aluminate cement (CAC)-bonded castables is crucial for the hydration of CAC and the conversion of hydration products in the curing and drying processes, as both the hydration and conversion reactions are dissolution-precipitation reactions. To elucidate the effect of different levels of free water loss upon the hydration of CAC, the conversion of hydration products and the mechanical strength of the CAC-bonded castables, the CAC-bonded castables were subjected to sealed and unsealed curing conditions at 50 ℃ and drying at 110 ℃. The results demonstrate that the fast removal of free water during unsealed curing would hinder the conversion from 2CaO·Al₂O₃·8H₂O to 3CaO·Al₂O₃·6H₂O and consequently prevent the deterioration of strength. As a comparison, although sealed-cured samples have less water loss and high degree of hydration of CAC, they still show lower strength than the unsealed samples after curing. The following drying process further accelerates the hydration of residual calcium aluminate clinkers for both the sealed and unsealed samples, but still does not favor the conversion from 2CaO·Al₂O₃·8H₂O to 3CaO·Al₂O₃·6H₂O in the unsealed-cured samples.
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  Effect of blade tilt angle on fluid flow characteristics in spray-blowing agitation composite process: a simulation

  Chao Lv, Hai-wei Zhang, Tao Yang, Hong-liang Zhao, Zhao-xiang Ji

  钢铁研究学报（英文版）. 2024, 31(9): 2142-2155.
  https://doi.org/10.1007/542243-024-01204-7

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  Aiming at the paddle tilt angle of the spray-blowing agitation composite process, the four-blade stirring and blowing composite desulfurization agitator was chosen as the research object, and the computational fluid dynamics numerical simulation was used to investigate the changes in flow field velocity, turbulent kinetic energy magnitude, and distribution caused by the blade tilt angle. Furthermore, the impact of blade tilt angle on the flow fragmentation behavior of individual bubbles and the coalescence process of multiple bubbles at different positions was studied. Under the same stirring and blowing process parameters, with the increase in the blade tilt angle of the agitator, the velocity of the flow field and the average turbulent kinetic energy inside the agitator decreased, and the bubble fragmentation speed decreased while the merging speed accelerated. The turbulent kinetic energy at the agitator bottom was greater when the blade tilt angle was 3.2° compared to when it was 13.2°, while the turbulent kinetic energy at the agitator upper part was relatively smaller. The results for single bubbles represented the state and trajectory of the bubble fragmentation process, and the results for multiple bubbles illustrated the state and trajectory of the bubble aggregation process.
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  A thermodynamic model for predicting activity of CaO-SiO₂-Al₂O₃- MgO-TiO₂-V₂O₃-FeO slags during electric furnace smelting process

  Jian-fa Jing, Shuai Wang, Yu-feng Guo, Feng Chen, Ling-zhi Yang, Jian-feng Yang, Fu-chun Xu

  钢铁研究学报（英文版）. 2024, 31(9): 2156-2172.
  https://doi.org/10.1007/s42243-024-01186-6

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  To optimize the comprehensive utilization of vanadium titanomagnetite by direct reduction-smelting processes, it is essential to acquire titanium slag with a higher TiO2 content of 45-60 wt.%. A thermodynamic model was developed based on the ion and molecule coexistence theory, specifically targeting the CaO-SiO₂-Al₂O₃-MgO-TiO_2-V₂O₃-FeO slag system. The impact of slag composition on the smelting of vanadium titanomagnetite was assessed, and the thermodynamic model was utilized to identify the optimal high-titanium slag. The results revealed that increasing the basicity, MgO content, and FeO content within the slag effectively suppressed the reduction of titanium and silicon oxides. Furthermore, the calculated activity coefficient of TiO2 decreased with higher basicity, MgO, and FeO levels. While an increase in basicity significantly enhanced the reduction of vanadium oxides, the effects of MgO and FeO contents on vanadium oxide reduction were comparatively less significant. Notably, higher basicity and FeO content promoted the formation of calcium titanates, whereas an elevated MgO content favored the formation of magnesium titanates. The smelting results indicated that a lower V₂O₃ content and higher TiO₂ activity corresponded to a smaller titanium mass fraction in the iron alloy, while the opposite trend was observed for vanadium.
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  Numerical simulation of nozzle structure to improve eccentric mold electromagnetic stirring in a round bloom mold

  Jian-li Wang, Yong-kun Yang, Jia-yu Zhu, Wei-an Wang, Liang Niu, Xiao-ming Li

  钢铁研究学报（英文版）. 2024, 31(9): 2173-2185.
  https://doi.org/10.1007/s42243-024-01192-8

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  A three-dimensional mathematical model coupling electromagnetic, flow, heat transfer, and solidification has been developed to investigate the effect of eccentric mold electromagnetic stirring (EM-EMS) on the flow and heat transfer of molten steel in round blooms with different cross sections. The uneven distribution of the flow field caused by EM-EMS was improved by changing the straight submerged entry nozzle (SEN) to a four-port SEN. The symmetry index was determined by the velocity distributions on the left and right sides of the center cross section of mold electromagnetic stirring (M-EMS), which quantitatively evaluated the symmetry of EM-EMS on the flow field. In the presence of EM-EMS, the maximum temperature difference of ø500 mm and ø650 mm round blooms between the inner and outer curves amounted to 63 and 26 K, respectively. The maximum distinction between the solidified shells in the inner and outer curves was 11.5 and 5.3 mm, respectively. After using the four-port SEN, the temperature and the shell distribution on the inner and outer curves for the ø500 mm round bloom were almost the same. The symmetry indices of ø500 mm and ø650 mm round blooms were increased from 0.55 and 0.70 to 0.77 and 0.87, respectively. The four-port SEN can be used to mitigate the negative impact of EM-EMS on the steel flow field.
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  Analysis model of internal residence time distribution for fluid flow in a multi-strand continuous casting tundish

  Qiang Yue, Yue Li, Zi-ming Wang, Ben-chen Sun, Xiu-zhen Wang

  钢铁研究学报（英文版）. 2024, 31(9): 2186-2195.
  https://doi.org/10.1007/s42243-024-01189-3

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  The external residence time distribution (RTD) curve is extensively used to characterise fluid flow within the single-strand continuous casting tundish. Dead volume fraction determination typically relies on the external RTD curve to reveal macroscopic fluid flow behaviour. Based on the external RTD to effectively assess dead volume fractions and other fluid characteristics under conditions of internal non-uniform flow, an internal RTD was introduced. In a smooth pipe under laminar flow conditions, the dead region occupies 25% of the total volume, which is defined as the space between the pipe wall and a radius of 0.866 R₀ (where R₀ is the radius of pipe). Under turbulent flow conditions, the dead region only occupies 0.38% of the reactor’s internal volume, spanning from the pipe wall to a radius of 0.00189 R0. The results obtained using the external RTD method are consistent with the theoretical analysis. Experimental trials involving water were conducted to examine the flow of molten steel within a five-strand tundish. Subsequently, an analysis approach employing internal RTD was employed to evaluate fluid mixing within a multi-flow continuous casting tundish. Using the internal RTD method, the analysis revealed that the whole dead zone volume fraction of the intermediate package decreased from 26.9% to 18.9% after the addition of the flow control device. The dead volume fraction can be accurately depicted by utilising the internal mean RTD function. The association between the internal RTD function and the external average RTD can be effectively employed to scrutinise the response curve of the tracer within a system exhibiting uneven flow distribution.
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  Microstructure evolution and its influence on thermoplasticity of wide and thick continuous casting slab with heavy reduction

  Tian-ci Chen, Xin Hu, Tan Zhao, Cheng Ji, Miao-yong Zhu

  钢铁研究学报（英文版）. 2024, 31(9): 2196-2206.
  https://doi.org/10.1007/s42243-024-01188-4

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  After the heavy reduction (HR) process was carried out at the solidification end of the continuous casting slab, the austenite grains were refined by recrystallization, which improved the thermoplasticity of the slab. However, the reduction in deformation during the HR process initiated stress concentration at the slab surface, and the crack risk increased. To effectively evaluate the risk of slab surface cracks under these complex conditions, the effect of the HR on the austenite recrystallization and thermoplasticity of a microalloyed slab surface was investigated by 15-pass reduction thermal simulation according to the wide and thick slab continuous casting process. The softening fraction was introduced as a global internal variable to quantitatively analyze various recrystallized re-refined grains. After the critical strain reaches the critical strain of dynamic recrystallization, a variety of recrystallization modes alternately occur. Among them, the contribution rate of dynamic crystallization to the later refinement reaches more than 50%. The contribution rates of static recrystallization and metadynamic recrystallization to grain refinement are almost the same. The thermoplasticity of the slab surface first increases and then decreases with increasing reduction pass. It was verified by transmission electron microscopy that the main reason for the decrease in thermoplasticity is that the dislocation multiplication rate increases, resulting in a sharp increase in stress and a decrease in thermoplasticity.
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  Understanding thermal compression and deformation behavior of 3.15 wt.% Si non-oriented electrical steels prepared by sub-rapid solidification

  Hui-hui Wang, Wan-lin Wang, Hua-long Li, Sheng-jie Wu, Pei-sheng Lyu, Bao-jun Zhao, Chen-yang Zhu

  钢铁研究学报（英文版）. 2024, 31(9): 2207-2216.
  https://doi.org/10.1007/s42243-024-01303-5

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  Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels. However, research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel, particularly at varying strain rates, has yet to be fully understood. The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.% Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated. The findings reveal that increasing the deformation temperature enhances grain recrystallization, while the peak stress decreases with higher temperature. Furthermore, a lower strain rate favors dynamic recrystallization and reduces thermal stress. It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel, and the thermal activation energy is calculated to be 204.411 kJ/mol. In addition, the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.% Si non-oriented electrical steel were established.
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  Theoretical and numerical research on effect of tension mechanisms in strip flatness electromagnetic control rolling mills

  Ting-song Yang, Tie-heng Yuan, Wen-quan Sun, An-rui He, Chun-tao Qu

  钢铁研究学报（英文版）. 2024, 31(9): 2217-2235.
  https://doi.org/10.1007/s42243-024-01195-5

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  To achieve stable rolling, the influence of a tension mechanism of a large diameter ratio roll system on the rolling process of a strip flatness electromagnetic control rolling mill is studied. Through the analysis of the rolling deformation zone, the deformation zone composition form of a large diameter ratio roll system and a calculation formula of neutral angle under tension are proposed. To analyze the effect of front and post tensions on the rolling characteristic and the strip flatness control characteristic, a three-dimensional rolling finite element (FE) model of a large diameter ratio roll system with the function of roll profile electromagnetic control is established by FE software and verified by a strip flatness electromagnetic control rolling mill. Based on the model, the strip thickness characteristic, metal transverse flow, strip flatness state, and adjustment range of the loaded roll gap are analyzed for different front and post tensions setting values. The results show that changing the front or post tension setting values can improve the single-pass reduction rate of a large diameter ratio roll system and have little effect on the flatness control ability of the strip flatness electromagnetic control rolling mill.
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  Finite element model simulation and back propagation neural network modeling of void closure for an extra-thick plate during gradient temperature rolling

  Shun-hu Zhang, Wen-hao Tian, Li-zhi Che, Wei-jian Chen, Yan Li, Liang-wei Wan, Zi-qi Yin

  钢铁研究学报（英文版）. 2024, 31(9): 2236-2247.
  https://doi.org/10.1007/542243-023-01148-4

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  The void closure behavior in a central extra-thick plate during the gradient temperature rolling was simulated and a back propagation (BP) neural network model was established. The thermal-mechanical finite element model of the gradient temperature rolling process was first developed and validated. The prediction error of the model for the rolling force is less than 2.51%, which has provided the feasibility of imbedding a defect in it. Based on the relevant data obtained from the simulation, the BP neural network was used to establish a prediction model for the compression degree of a void defect. After statistical analysis, 80% of the data had a hit rate higher than 95%, and the hit rate of all data was higher than 90%, which indicates that the BP neural network can accurately predict the compression degree. Meanwhile, the comparisons between the results with the gradient temperature rolling and uniform temperature rolling, and between the results with the single-pass rolling and multi-pass rolling were discussed, which provides a theoretical reference for developing process parameters in actual production.
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  Modeling of strain-induced γ→α’ phase transformation for 201Cu metastable austenitic stainless steel and its verification in rolling processes

  Li-xia Xu, Long-hui Zhou, Hong-yun Bi, E Chang, Feng-li Sui

  钢铁研究学报（英文版）. 2024, 31(9): 2248-2254.
  https://doi.org/10.1007/542243-023-01152-8

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  To model the strain-induced γ→α’ phase transformation for the Cr-Mn metastable austenitic stainless steel, the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size of ø5 mm 9 10 mm were compressed at strains of 0.2-0.6 in the temperature range of 25-150 ℃ and in the strain rate range of 0.1-5.0 s^-1 . The flaky samples were prepared by wire cutting from the cylindrical samples and the volume fraction of the strain-induced a0 phase was detected in the test point of the flaky samples. The volume fraction changing with the process parameters was modeled, and the critical temperatures and the critical strains to prevent γ→α’ phase transformation were calculated as other different process parameters changed. The linear fitting goodness of the model between the calculated volume fraction values and the tested ones is 0.986 and the validity of the model was verified by application in cold and warm rolling experiments.
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  Mechanisms of strength-plasticity enhancement and stress-induced phase transition in a medium-carbon low-alloy steel

  Meng-wei Lu, Xin Chen, Wen-xi Liu, Yu-ru Chen, Qi Li, Kai Wang, Zu-min Wang, Yuan Huang

  钢铁研究学报（英文版）. 2024, 31(9): 2255-2270.
  https://doi.org/10.1007/542243-023-01153-7

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  A medium-carbon low-alloy steel with designed chemical composition was investigated. The steel exhibits an excellent product of strength and elongation value of 31,832 MPa% through quenching and partitioning treatment, with a tensile strength of 1413 MPa and elongation of 22%. X-ray diffraction analysis and transmission electron microscopy characterizations confirm that the retained austenite in the specimens undergoes stress-induced phase transformation to the martensite and hexagonal phases, namely the transformation-induced plasticity (TRIP) effect is triggered. This TRIP effect, triggered by the stress-induced phase transition of retained austenite, is responsible for the excellent mechanical properties obtained in the steel. For further investigating the stress-induced phase transition mechanism, thermodynamic methods are applied. Gibbs free energy of face-centered cubic-Fe, ε-Fe, ω-Fe and body-centered cubic-Fe associated with the stressinduced phase transition was calculated using molecular dynamics simulations, and a calculation method of strain energy in thermodynamic units for the stress-induced martensitic transformation is presented. The final results reveal the process and thermodynamic mechanism of stress-induced martensitic transformation in medium-carbon steels, in which the hexagonal phase can participate in the process as an intermediate product.
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  Hot deformation behavior and hot-metal-gas-forming process of V micro-alloyed high manganese steel

  Yong-gang Yang, Wang-nan Zuo, Mei Xu, Chang-hui Yuan, Jiang Chang, Lei Qi, Zhen-li Mi

  钢铁研究学报（英文版）. 2024, 31(9): 2271-2280.
  https://doi.org/10.1007/542243-023-01136-8

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  The hot deformation behavior of a newly designed V micro-alloyed high manganese steel (HMnS) was investigated in order to guide the development of the hot-metal-gas-forming process. Single-pass hot compression experiments were conducted in the temperature range of 950-1100 ℃ and the strain rate range of 0.05-10 s^-1 , and the stress-strain curves and the corresponding softening mechanism of the V micro-alloyed HMnS were analyzed. Results show that two types of stress-strain curves, representing the work hardening (WH)-dynamic recovery (DRV)-dynamic recrystallization (DRX) mechanism and the WH-DRV mechanism, respectively, occur during the deformation process. Moreover, the WH-DRV- DRX mechanism gradually transforms into the WH-DRV mechanism with the increasing strain rate and decreasing deformation temperature. Two types of constitutive models considering the softening mechanism difference were established and verified by additional hot-deformation experiments. Hot processing map of the HMnS was established and correlated well with the microstructure evolution result. Based on the constitutive models and processing map, the optimal processing parameter range and flow stress of HMnS for the hot-metal-gas-forming were determined.
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  Pitting corrosion initiated by SiO₂-MnO-Cr₂O₃-Al₂O₃-based inclusions in a 304 stainless steel

  Jin-zhen Hu, Shi Li, Ji Zhang, Ying Ren, Li-feng Zhang

  钢铁研究学报（英文版）. 2024, 31(9): 2281-2293.
  https://doi.org/10.1007/s42243-023-01101-5

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  The influence of the aluminum content on the pitting corrosion of a 304 stainless steel by a Cl^- solution was investigated. The number, area, and composition of non-metallic inclusions were modified by the addition of aluminum in the steel, which was responsible for the variation of the corrosion degree of the 304 stainless steel. Inclusions detection, corrosion test, electrochemical test, thermodynamic calculation, and first-principles calculation were performed to evaluate the pitting corrosion of the stainless steel. The initiation of the pitting corrosion by three types of inclusions, including (Mn, Si, Cr, S)O, (Mn, Al, Cr)O, and Al₂O₃ were in-situ observed. After corroding for 880 min, the corrosion index of (Mn, Si, Cr, S)O, (Mn, Al, Cr)O, and Al₂O₃ was 0.38%, 0.02%, and 0.00% min^-1 , respectively. With the increase in aluminum content in the steel, the pitting potential of the stainless steel was 0.131, 0.304, and 0.338 V, respectively, indicating that a higher aluminum content in the steel was beneficial to improving the pitting corrosion resistance of the 304 stainless steel.
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  Corrosion mechanism of Zn-Al-Mg-coated steel in simulated polluted marine atmosphere

  Pei-dong Ning, Li-yuan Xiao, Jin Wang, Qian-qian Liu, Kui Xiao

  钢铁研究学报（英文版）. 2024, 31(9): 2294-2307.
  https://doi.org/10.1007/s42243-024-01210-9

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  The corrosion behaviour of zinc-aluminium-magnesium-coated steel in a simulated polluted marine atmospheric envi-ronment was investigated. Therefore, an indoor ageing acceleration test was carefully designed by simulating a polluted marine environment. The objective was to in-depth investigate the corrosion mechanism of Zn-Al-Mg-coated steel exposed to a simulated polluted marine environment. The experiments were carried out by scanning electron microscopy for micro-morphological characterization, X-ray diffraction, electrochemical impedance spectroscopy and electrodynamic polarization curves for the aged samples. The analysis of the results obtained after an indoor accelerated ageing test shows that Zn-Al-Mg coatings generate insoluble Zn₅Cl₂(OH)₈·H₂O and Zn₄SO₄(OH)₆ during the corrosion process, which hinders the diffusion of corrosive substances into the substrate, and the insoluble substances are structurally dense and thus inhibit further corrosion. Therefore, this effectively inhibits the occurrence of further corrosion, and thus, Zn-Al-Mg coating can significantly extend the service life of Zn-Al-Mg-coated steel.
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  Microstructure and microtexture evolution characteristics of a powder metallurgy Ni-based superalloy during static recrystallization

  Zhi-qiang Li, De-cheng Wang, Yue-wen Zhai, Chao Jiang, Le-yu Zhou, Zhi-guang Zhou, Hui-zhen Wang, Zi-bo Zhang, Lin Yan, Li-ping Wang, Guang Yu

  钢铁研究学报（英文版）. 2024, 31(9): 2308-2325.
  https://doi.org/10.1007/s42243-024-01217-2

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  Static recrystallization (SRX) characteristics of a powder metallurgy superalloy were investigated by isothermal compression at 1080-1170 C under strain rates of 0.01-0.1 s^-1 , strains of 0.1, 0.22, or 0.5, and holding time of 0-300 s. The impacts of temperature, strain rate, holding time, and strain on the SRXed grain size, volume fraction, and microtexture were explored by electron backscatter diffraction technique. It was found that temperature played a key role in these processes. As SRX progressed, the <110> fiber parallel to the axis compression direction gradually weakened and was replaced by the <001> fiber because <001> was the preferred recrystallization orientation and grain growth direction for the Ni-based superalloy. Moreover, high temperatures and low strain rates promoted the formation of the <001> fiber. Three nucleation mechanisms during SRX process were found: grain boundary bulging, primary twin assistance, and subgrain coalescence. Grain boundary bulging occurred under all process conditions; however, at low temperatures and high strain rates, the latter two mechanisms could provide additional nucleation modes. In addition, SRX size and volume fraction models were established.