2021年, 第28卷, 第1期　刊出日期：2021-01-25

  

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  Gasification reactivity and kinetic parameters of coal chars for non-isothermal steam gasification

  Ya-jie Wang, Hai-bin Zuo, Jun Zhao, Guang-wei Wang

  钢铁研究学报(英文版). 2021, 28(1): 1-9.
  https://doi.org/10.1007/s42243-020-00463-4

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  The gasification reactivity and kinetic parameters of coal chars for non-isothermal steam gasification were investigated. One kind of lignite and three kinds of bituminous coals were used as the samples, and their coal ranks follow the ascending order: XB< KL<  ZJ<  GD. As characterized by the comprehensive gasification index, the gasification reactivity of coal chars follows the descending order: XB>KL>ZJ>GD. Through systematically analyzing factors affecting gasification reactivity, it was ascertained that the gasification reactivity is mostly determined by the carbonaceous structure. The gasification reactivity is inversely proportional to the coal rank, and the higher the coal rank, the lower the gasification reactivity. A new kinetic model was proposed to calculate the kinetic parameters, in which the reaction order was considered as an unknown kinetic parameter. The reaction order n follows the ascending order: XB< KL<ZJ <GD, which are n = 1.00, n = 1.34, n = 1.83, and n = 2.63, respectively. It is proved that the reaction order is proportional to the coal rank, and the higher the coal rank, the higher the reaction order.
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  Numerical investigation of breakup process of molten blast furnace slag through air quenching dry granulation technique

  Li-li Wang, Yu-zhu Zhang, Yue Long

  钢铁研究学报(英文版). 2021, 28(1): 10-18.
  https://doi.org/10.1007/s42243-020-00483-0

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  Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique. The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery. In order to gain deep insight into the granulation mechanism and visualize the breakup process, three-dimensional unsteady numerical simulation based on the k-x based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag (k is the turbulent kinetic energy, and x is the specific dissipation rate). The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface. The results show that a flat film is formed firstly under the effects of air impingement, recirculation zone and pressure gradients. Then, the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough. Finally, the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface. The droplets smaller than 3.00 mm account for 80%, with the average diameter of 1.95 mm.
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  Two-dimensional comprehensive mathematical model for electroslag remelting process with pipe electrode

  Wen‑jie Tong, Wan‑ming Li, Xi‑min Zang, Peng Wang, Hua‑bing Li, De‑jun Li

  钢铁研究学报(英文版). 2021, 28(1): 19-28.
  https://doi.org/10.1007/s42243-020-00426-9

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  Taking the electroslag remelting with pipe electrode (ESR-PE) and electroslag remelting with solid electrode (ESR-SE) as the research objects, a two-dimensional steady-state mathematical model of coupled electromagnetic field equation, energy equation, and flow equation was established. The distribution of its current density, Joule heat, flow field, and temperature field was compared and the difference of their molten metal pool was analyzed. The results show that compared with those of ESR-SE, current density distribution and Joule heating area of ESR-PE are mainly concentrated in the inner and outer wall areas of the electrode tip, while the Joule heat generated in the central area of the slag pool is less. In the ESR-PE, the slag flows from the outside of the electrode to the hollow area of the electrode, which makes the temperature distribution in the slag pool is more uniform. Affected by the Joule heating area and flow field, the heat of ESR-SE is concentrated below the electrode in the slag pool area and it transfers from the center to the periphery. However, in the ESR-PE, the heat is concentrated near the inner and outer walls of the electrode tip, and the heat is transferred from the periphery to the center of the slag pool. The molten metal pool depth of ESR-SE is 0.1188 m and that of ESR-PE is 0.0962 m. Compared with that of ESR-SE, the molten metal pool of ESR-PE is shallower and flatter.
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  Separation and enrichment mechanism of C54–TiSi₂ from hypoeutectic Ti–65 wt.% Si alloy during directional solidification via alternating electromagnetic fields

  Kui‑song Zhu, Jing‑fei Hu, Wen‑hui Ma, Kui‑xian Wei, Yong‑nian Dai

  钢铁研究学报(英文版). 2021, 28(1): 29-37.
  https://doi.org/10.1007/s42243-020-00365-5

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  The effects of directional solidification parameters and the coupling of directional solidification parameters and alternating electromagnetic fields on separation and enrichment of the C54–TiSi₂ phase were investigated in a directionally solidified hypoeutectic Ti–65 wt.% Si alloy. The results indicated that by increasing the pull-down velocity at a given position within the ingot, the cooling rate, growth rate, and temperature gradient of ingot could be increased. At a pull-down velocity near 5 μm/s, the temperature gradient, cooling rate, and growth rate decreased with increasing the thickness of the C54–TiSi₂- rich layer. Electromagnetic fields enhanced mass transfer at pull-down velocities of 5, 10, 15, and 20 μm/s, with resulting enriched layer thicknesses of 15, 10, 10, and 5 mm, respectively. By increasing the percentage of Ti in the Ti–Si alloy from 25 to 35 wt.%, the thickness of the C54–TiSi₂-rich layer was increased from 2.5 to 3.3 cm. However, the maximum C54–TiSi₂ content obtained experimentally in this layer decreased from 92.06 to 79.49 mass%.
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  Comparison study of slag corrosion resistance of MgO–MgAl₂O₄, MgO–CaO and MgO–C refractories under electromagnetic field

  Xin‑ming Ren, Bei‑yue Ma, Shi‑ming Li, Hong‑xia Li, Guo‑qi Liu, Wen‑gang Yang, Fan Qian, Shi‑xian Zhao, Jing‑kun Yu

  钢铁研究学报(英文版). 2021, 28(1): 38-45.
  https://doi.org/10.1007/s42243-020-00421-0

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  To illuminate the corrosion behavior of MgO-based refractories under electromagnetic field (EMF), herein, the slag corrosion and penetration resistance of MgO–MgAl₂O₄, MgO–CaO, and MgO–C refractories were investigated using the rotary immersion slag resistance test at 1873 K for 1 h. The results showed that the order of the good slag resistance of as-tested refractories was MgO–C > MgO–CaO > MgO–MgAl₂O₄. The EMF accelerated the corrosion and penetration of slag to the refractories, which caused the molten slag to be easier into the refractories by natural convection and Marangoni effect. In addition, the MgO–C refractories did not show an overwhelming advantage in slag resistance because EMF impeded the formation of the dense protection layer. Consequently, in view of the present results, the MgO–C refractories are still the most promising slag line material for refining furnace among MgO–MgAl₂O₄, MgO–CaO, and MgO–C refractories.
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  Metadynamic recrystallization behaviors of SA508Gr.4N reactor pressure vessel steel during hot compressive deformation

  Shi-bin Qiao, Zheng-dong Liu, Xi-kou He, Chang-sheng Xie

  钢铁研究学报(英文版). 2021, 28(1): 46-57.
  https://doi.org/10.1007/s42243-020-00410-3

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  The metadynamic recrystallization (MDRX) model is established, and the coefficients determined by multiple linear regression analysis are used to describe the microstructure evolution of SA508Gr.4N steel. The effects of compression temperature of 950–1150 ℃, strain rate of 0.001–0.1 s^-1, pre-strain of 0.3–0.6, initial austenite grain size (IAGS) of 136–552 lm, and interval time of 1–300 s on the MDRX kinetics and microstructure evolution were analyzed, using twopass compression test method on Gleeble thermo-mechanical simulator. The results show that MDRX kinetics and austenite grain size are strongly dependent on compression temperature and strain rate, MDRX volume fraction increases with increasing compression temperature and strain rate, and the grain size decreases with increasing strain rate and decreasing compression temperature, while less affected by the pre-strain and IAGS. Meanwhile, the values predicted using MDRX model and the ones calculated from experiment are compared, and the results show that the proposed model can give a reasonable estimate of MDRX behavior for SA508Gr.4N steel.
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  Simulation and verification of core–shell MC carbide design in Fe–C–Ni–V–Ti steel

  Chen‑chong Wang, Chun‑guang Shen, Zhen Zhang, Wei Xu

  钢铁研究学报(英文版). 2021, 28(1): 58-65.
  https://doi.org/10.1007/s42243-020-00451-8

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  Thermodynamic theory was used to calculate the formation temperature and site fraction of MC carbides in Fe–C–Ni–V–Ti system. The calculation results showed the theoretical formation conditions of core–shell MC carbides. One-step and two-step heat treatment processes were used in Fe–C–Ni–V–Ti alloy to, respectively, obtain homogeneous and core–shell MC carbides, which was consistent with the thermodynamic calculation results. The transmission electron microscopy observations showed that the core–shell MC carbide obtained by the two-step heat treatment process contained homogeneous (Ti, V)C as the core and basically VC as the shell. The mechanical test results proved that compared with homogeneous MC carbides, core–shell MC carbides could improve the basic mechanical properties of the alloy because VC shell greatly increased the bonding strength and separation work of Fe/MC interface. Thus, the core–shell MC carbide with a VC shell structure can be a better grain refiner and can be used in steels with a high standard of fracture toughness.
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  Microstructure evolution of ultra-high-strength twinning-induced plasticity (TWIP) steel under dynamic loading

  Qi‑hang Pang, Mei Xu, Zhen‑li Mi, Juan Cui, Jing Guo

  钢铁研究学报(英文版). 2021, 28(1): 66-75.
  https://doi.org/10.1007/s42243-020-00457-2

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  To prepare ultra-high-yield strength twinning-induced plasticity (TWIP) steel and reveal its work hardening mechanism at different strain rates from the microcosmic range, the microstructure evolution mechanism of Fe–20Mn–0.6C TWIP steel was investigated at strain rates of 10^-4–103 s^-1 using a high-speed tensile testing machine and a transmission electron microscope. The results show that the strain rate and deformation had a significant effect on the twin morphology of TWIP steels. At a strain rate of 102 s^-1, secondary deformation twins were developed, which intersected with the initial deformation twins and increased the resistance of dislocation movement, as well as the plasticity. TWIP steel at a strain rate of 102 s^-1 had a higher twin formation speed than that at 100 s^-1. At the same amount of deformation, the twin boundary fraction was higher and increased linearly at a strain rate of 102 s^-1, while the rule of twin growth at 100 s^-1 was conformed to S-curve change of DoseResp model.
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  Constitutive modeling and analysis on high-temperature flow behavior of 25 steel

  Wei Wei, Chao-long Yuan, Ren-dong Wu, Wei Jiao, Ding-chuan Liang

  钢铁研究学报(英文版). 2021, 28(1): 76-85.
  https://doi.org/10.1007/s42243-020-00445-6

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  The constitutive relationship is the basis for studying the material processing technology and controlling the quality of products. Data and models of the plastic flow behavior of materials are often required during the manufacturing process. Therefore, establishing constitutive models with high precision and generalization and enriching material database is of great significance for optimizing processing technology and product quality of the material. Based on the Gleeble thermal compression test results, the essential relationship of 25 steel between the flow stress and thermal–mechanical state variables, such as temperature, strain rate, and strain, is quantitatively discussed for the first time. Combined with the Zener–Hollomon parameter and considering the influence of strain compensation, the constitutive model of 25 steel is built by the hyperbolic-sine equation over the full strain range. In the modeling process, the influence of strain on material constants is characterized by polynomial fitting. The selection basis of polynomial order is discussed in-depth, and the inconsistency between calculation accuracy and fitting effect is clarified. Finally, the accuracy of the model is analyzed, and the generalization and applicability are discussed. It is proved that the developed model can accurately predict the flow behavior of materials in the full strain range.
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  Ratcheting behavior of notched stainless steel samples subjected to asymmetric loading cycles

  A. Shekarian, A. Varvani‑Farahani

  钢铁研究学报(英文版). 2021, 28(1): 86-97.
  https://doi.org/10.1007/s42243-020-00465-2

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  The ratcheting response of 316 stainless steel samples at the vicinity of notch roots under single- and multi-step loading conditions is evaluated. Multi-step tests were conducted to examine local ratcheting at different low–high–high and high–low–low loading sequences. The stress levels over loading steps and their sequences highly influenced ratcheting magnitude and rate. The change of stress level from low to high promoted ratcheting over proceeding cycles while ratcheting strains dropped in magnitude for opposing sequence where stress level dropped from high to low. Local ratcheting strain values at the vicinity of notch root were found noticeably larger than nominal ratcheting values measured at farer distances from notch edge through use of strain gauges. Ratcheting values in both mediums of local and nominal were promoted as notch diameter increased. To assess progressive ratcheting response and stress relaxation concurrently, the Ahmadzadeh-Varvani (A-V) kinematic hardening rule was coupled with Neuber’s rule enabling to calculate local stress at notch root of steel samples. Local stress/strain values were progressed at notch root over applied asymmetric stress cycles resulting in ratcheting buildup through A-V model. The relaxation of stress values at a given peak-valley strain event was governed through the Neuber’s rule. Experimental ratcheting data were found agreeable with those predicted through the coupled framework.
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  Role of carbon in modifying solidification and microstructure of a Ni?based superalloy with high Al and Ti contents

  Guang‑di Zhao, Xi‑min Zang, Wen‑ru Sun

  钢铁研究学报(英文版). 2021, 28(1): 98-110.
  https://doi.org/10.1007/s42243-020-00408-x

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  The effect of carbon ranging from 0.014 to 0.071 wt.% on the solidification and microstructure of a Ni-based superalloy with high Al and Ti contents was studied. The results show that the increase in carbon addition significantly increases the size and volume fraction of MC carbides and promotes the change of their morphology from blocky to elongated shape. However, the carbon addition obviously decreases the size and volume fraction of eutectic (γ+ γ′) and reduces η phase and borides formation. The change in carbide characteristics is mainly because of the increasing carbide-forming element and carbides precipitation temperature with the increase in carbon which favors the growth of them along the interdendritic liquid film. MC carbides are formed at an earlier solidification stage than the eutectic (γ +γ′). The increased carbide formation consumes more Ti, which delays and reduces the eutectic (γ + γ′) precipitation. The delay of eutectic (γ + γ′) precipitation leads to a deeper undercooling, which significantly decreases the critical Ti concentration for its precipitation. This, in turn, lowers Ti/ Al ratio in residual liquids ahead of the eutectic (γ + γ′) and hence reduces η formation subsequently. B and Zr are slightly enriched in the carbides, which are considered during discussing how carbon influences the eutectic (γ + γ′) precipitation.
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  Printability and physical properties of iron slag powder composites using material extrusion?based 3D printing

  Hyungjin Kim, Sangkyu Lee

  钢铁研究学报(英文版). 2021, 28(1): 111-121.
  https://doi.org/10.1007/s42243-020-00475-0

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  There have been many studies on three-dimensional (3D) printing using metal compounds. However, 3D printing using a metal compound has disadvantages in that it increases the cost for supplying metal materials. A method of using slag which is a recyclable material has been proposed to reduce costs. With the growing demand for additive manufacturing using byproducts, slag has gained attention as a diverse recycling material for 3D printing technologies. A new fabrication approach was analyzed for producing porous bodies via additive manufacturing for blending slag and reinforced metals. However, because of its low quality due to low strength, low durability, and structural defeats, the amount of slag generated is high, and its usability remains uncertain. Also, slag is an excellent material with a huge potential for producing structures with high mechanical properties, and limited research in the area of slag recycling has been conducted due to difficulties in sintering the iron by-products. To develop a recycling approach that utilizes slag in 3D printing powders, a study to increase the industrial usability by mixing slag and ceramic beads was described. A method was presented to compare the physical properties of 3D printed slag parts with the physical properties of those generated by blending iron slag, alumina, and zirconia. In order to find the mixing ratio with the optimum physical properties, the average particle size, bending stress, and maximum compressive stress were tested. The combination ratio to obtain the highest strength was when iron slag powder was 40% and alumina was 60%. In addition, the specimens by composition to which the stress test was applied were cut to analyze the tissue under a microscope. It is thought that cracking in the sintered structure decreases and density increases by mixing alumina and zirconium, contributing to increased strength. When a ceramic bead composed of alumina and zirconium is mixed with slag to form a composite material, a metal compound having a level of physical properties that can be used as a material for 3D printing can be produced. Furthermore, a novel concept of producing lightweight structural materials via additive manufacturing, which entails a fabrication process whereby high-strength metals are stacked inside hollow base steels, was proposed.