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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Advance Publication

  • Accuracy Evaluation of Phase-field Models for Grain Growth Simulation with Anisotropic Grain Boundary Properties

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    DOI:10.2355/isijinternational.ISIJINT-2019-305

    The phase-field method has been widely employed recently for simulating grain growth. Phase-field grain growth models are classified into two types according to their conservation constraints for phase-field variables: the multi-phase-field model and the continuum-field model. In addition, within the multi-phase-field model framework, three models with different formulations exist. These models are reported to accurately simulate grain growth under conditions of isotropic or weakly anisotropic grain boundary energy and mobility. However, for cases of strongly anisotropic grain boundary properties, the accuracy of these models has not yet been examined in detail. In this study, using the continuum-field model and three different multi-phase-field models, systematic grain growth simulations with anisotropic grain boundary energies and mobilities are performed. Through the detailed investigation of the accuracy of the simulated results, the suitability of each model for anisotropic grain growth simulations is revealed. Furthermore, based on the higher-order terms, accuracy improvement of the phase-field models is attempted.
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    Readers Who Read This Article Also Read

    1. Reaction Behavior of Coke in a High Alumina Slag ISIJ International Advance Publication
    2. Shrinkage Distribution of Sintering Bed Evaluated by X-ray CT Observation ISIJ International Advance Publication
  • Reaction Behavior of Coke in a High Alumina Slag

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    DOI:10.2355/isijinternational.ISIJINT-2019-180

    The reaction behaviors between coke and CaO–SiO2–MgO–Al2O3–Cr2O3 slag at different immersion time, temperature and rotation speeds were studied in this work. The diameter decrement of the coke increased as increasing the immersion time, temperature and rotation speed. When the coke was in contact with the molten slag, the slag could infiltrate into the coke and further flow to the interior of the coke through pore channels, which will fill up the coke pores. During the penetration process of slag into the coke, the carbon could be oxidized by Cr2O3 and SiO2 in the slag. Furthermore, the penetrated slag could also dissolve the coke ash minerals and react with that to form new phase. The comprehensive effects of slag penetration, slag-carbon reaction and slag-mineral reaction eventually resulted in the coke degradation.
  • Artificial MnS Inclusions in Stainless Steel: Fabrication by Spark Plasma Sintering and Corrosion Evaluation by Microelectrochemical Measurements

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    DOI:10.2355/isijinternational.ISIJINT-2019-408

    Spark plasma sintering was used to fabricate type 304L stainless steel specimens containing artificial manganese sulfide (MnS) inclusions, and a microelectrochemical technique was used to characterize the pit initiation behavior at the MnS. A 200 μm square electrode area that included an artificial MnS particle was potentiodynamically polarized in 0.1 M NaCl, and the electrode surface was observed in situ by optical microscopy. The anodic dissolution of the MnS particle was observed in the passive region of the stainless steel. The pit occurred at the boundary between the particle and the steel matrix after the particle dissolved slightly. The dissolution potential and pit initiation behavior at the artificial MnS particles in the sintered stainless steel were confirmed to be similar to those at MnS inclusions in commercial stainless steels.
  • Atomic and Effective Pair Interactions in FeC Alloy with Point Defects: A Cluster Expansion Study

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    DOI:10.2355/isijinternational.ISIJINT-2019-019

    The Cluster Expansion Method (CEM) is used to investigate the pair interactions in body centered cubic (BCC) FeC alloy in the presence of vacancies. Within the CEM framework, the relation of cluster (point and pair) probabilities and set of independent correlation functions are derived. These are then applied to calculate the effective cluster interaction and atomic pair interaction energies for Fe, C and vacancy in FeC system. We found that, in this alloy, the interaction mostly comes from the first nearest neighbor pairs, and, to some degree, from the third nearest neighbor pairs. Detailed analysis shows that, within the first nearest neighbor pair interactions approximation, the C–C and Fe–C pair interactions are repulsive where the former one is more dominant. This is attributed to the local stress field formed in the vicinity of C atoms which pushes the first nearest neighbor atoms away to maintain the equilibrium distances. Moreover, there is an attractive interaction between C and vacancy which implies the possibility of C atoms to be trapped at vacancy site.
  • Reduction and Gasification Characteristics of A Unique Iron Ore/carbon Composite Prepared from Robe River and A Coal Tar Vacuum Residue

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    DOI:10.2355/isijinternational.ISIJINT-2019-048

    We have prepared a unique iron ore/carbon composites (IOC) from a low grade iron ore called Robe River and a thermoplastic carbonaceous material. When Robe River which contains iron as goethite, FeOOH, is heated up to 250 to 300°C, the OH groups are removed as H2O, leaving flat pore spaces of 0.8 nm wide between 2.0 nm thick Fe2O3 layers. The pore spaces are, however, closed over 300°C by the sintering of the Fe2O3 layers. The idea proposed is to insert the thermoplastic carbonaceous material into the pore space of 0.8 nm wide while the pore spaces are opened and to carbonize it to form carbon in the pore space below 500°C. The iron oxide in the IOC thus prepared is reduced very rapidly in inert atmosphere and the carbon retained in the pore space is gasified by CO2 very rapidly also. In this work the reaction characteristics of the unique iron ore/carbon composite prepared from Rove River and a coal tar vacuum residue, CTVR, were examined for its direct reduction, indirect reduction in a H2 atmosphere, and coke gasification in a CO2 atmosphere from the viewpoints of reaction enthalpies and rate parameters. The examinations clarified that the carbonaceous material retained as coke in the pore space of iron ore are very reactive and show reaction characteristics different from bulk carbon.
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    1. Atomic and Effective Pair Interactions in FeC Alloy with Point Defects: A Cluster Expansion Study ISIJ International Advance Publication
  • Influence of Ambient and Oxygen Temperatures on Fluid Flow Characteristics Considering Swirl-type Supersonic Oxygen Jets

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    DOI:10.2355/isijinternational.ISIJINT-2019-030

    In vanadium extraction converter steelmaking, the swirl-type oxygen lance has been applied to improve the dynamic condition of the molten bath reaction to achieve a higher oxidation rate of vanadium and better vanadium slag quality, because the swirl-type jet can generate not only axial and radial forces but also tangential ones. Recently, the swirl-type supersonic jet with preheated oxygen was proposed to further enhance the agitation ability of the oxygen jet on the molten bath. In this study, the effects of the ambient temperature and oxygen temperature on the swirl-type supersonic jet behavior were analyzed to achieve better formulation and optimization of the process parameters. The flow characteristics of swirl-type oxygen jets were simulated by computational fluid dynamics software at 300 K, and 1700 K ambient and 300 K, 450 K and 600 K oxygen temperature, and partial results were validated against data from a preheating jet experiment. An analysis of the results shows that the centerline jet velocity was increased by preheated oxygen, and at higher ambient temperature, a longer core length was formed and the velocity fluctuation was aggravated. The influence of the preheating temperature on the core length was more evident at lower ambient temperature. From a dynamic perspective, the molecular motion was improved and with respect to energy, the internal energy of the oxygen jets could be preserved at higher ambient temperature.
  • Effect of a Novel Hot-core Heavy Reduction Rolling Process after Complete Solidification on Deformation and Microstructure of Casting Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-125

    Hot-core Heavy Reduction Rolling (HHR2) is a novel technology designed for eliminating center defects of casting steel by using the large temperature gradient, which performed heavy reduction to bloom or slab with rolling mill after the position of solidification end of the strand. This works mainly focus on the effect of HHR2 process on the shrinkage elimination and microstructure evolution. Firstly, bonding plate rolling experiment were carried out, which proved HHR2 process with large temperature gradient in thickness direction could improve the internal deformation of workpiece. Meanwhile, the deformation permeability was beneficial to the microstructure refinement of center layer. Secondly, the HHR2 process was studied by analysis of the results of FEM to explore the influence of some process parameters on shrinkage closure. In this study, the Gm index and volumetric residual percentage V/V0 were used as evaluation index in mechanical analyses and quantitative comparison, the results reflected the void tend to closing with the reduction ratio and roll diameter increasing, as well as with the reduction position moving towards the solidification end after complete solidification. Finally, the pilot plant trail of HHR2 was carried out before industrial application, and the results reflects the HHR2 process can eliminate the large central shrinkage cavity and refine the center microstructure.
  • Fabrication of Iron Oxide Nanoparticles via Submerged Photosynthesis and the Morphologies under Different Light Sources

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    DOI:10.2355/isijinternational.ISIJINT-2019-188

    Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO and CuO nanostructures have been successfully fabricated via this method. In this work, the SPSC process was applied for the fabrication of iron oxide and hydroxide nanoparticles. The experiments were conducted under visible light, ultraviolet light, and gamma-ray irradiation conditions and the morphologies of the obtained nanoparticles were observed and compared with that obtained without illumination. Then, the mechanism of the SPSC process for the fabrication of iron oxide nanoparticles was discussed. The results show that various kinds of morphologies of nanocrystallites were obtained on the Fe plate surface and the main morphologies are different under different conditions. For example, most FeOOH with the morphologies of nanorod and nanofiber exist by visible light irradiation; most faceted crystals of FeOOH and Fe2O3 with the morphologies of nanograular and nanorod exist by ultraviolet irradiation. In the SPSC process, light irradiation generates ·OH at the crystal tips and promote the crystallization in apical growth of FeOOH.
  • Characterization and Properties of Scaffold in a Dissected Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2019-199

    The blast furnace scaffold can only be obtained while the blast furnace shut down after operating for many years. Its characteristics and properties are important for the blast furnace campaign life. The key to delaying the carbon brick corrosion in blast furnace hearth is the scaffold formed between the melt and the carbon brick. In an emergency shutdown blast furnace, the scaffold in hearth is completely preserved, and the scaffold on the surface of the carbon brick above and below the taphole in hearth are sampled. The purpose of this study is to describe the characterization and properties of the scaffold in hearth. The paper presents results from investigations using electron imaging techniques such as Transmission Electron Microscopy (TEM), Optical Microscope (OM), Scanning Electron Microscope combined with Energy Dispersive Spectrometer (SEM-EDS), Raman analysis and X-ray Diffraction (XRD). The main component of the slag skull above the taphole is similar to the final slag and is rich in harmful elements. The thermal conductivity of the scaffold is about 2 W/(m·K) and the viscosity as well as the solidus temperature are higher than the final slag. The slag skull acts to isolate and contain harmful elements. The phase on the hot surface of the carbon brick below the taphole is mainly consist of graphite and the large-grained graphite phase has a random spatial network distribution in the iron matrix. The slag skull and the graphite serves to segregate the melt and harmful element, thereby protecting the carbon brick and extending hearth life.
  • Numerical Analysis of the Effect of Water Gas Shift Reaction on Flash Reduction Behavior of Hematite with Syngas

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    DOI:10.2355/isijinternational.ISIJINT-2019-215

    The water gas shift reaction (WGSR) is the most important side reaction in direct iron reduction processes in syngas. In this study, an Euler-Lagrange model has been developed to simulate the flash reduction behavior of hematite with syngas in a drop tube reactor. Based on model validation, the effect of WGSR on the flash reduction is investigated by comparing results predicted by models with and without WGSR. Results indicate that the WGSR has a minor effect in CO–H2 system while a major effect in H2–CO–CO2–H2O system. The difference of gas composition caused by WGSR leads to a difference of gas reduction capacity, which results in different reduction behavior. The relationship between the composition of gas mixture and the equilibrium constant of WGSR determines the direction of WGSR and thus determines the positive or negative effect of WGSR on the reduction process. The higher oxygen partial pressure and temperature, the stronger influence of WGSR can be considered to have.
  • Numerical Simulation of Multiphase Flow and Mixing Behavior in an Industrial Single Snorkel Refining Furnace: Effect of Bubble Expansion and Snorkel Immersion Depth

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    DOI:10.2355/isijinternational.ISIJINT-2019-280

    A coupled mathematical model is used to simulate the multiphase flow in an industrial Single Snorkel Refining Furnace (SSRF). Based on the present model, the evolution characteristics of bubble size, density, and velocity are analysed during the long-distance rising process. The comparative studies indicate that the expansion of bubbles has an enormous impact on the circulation rate and free surface in the vacuum chamber. Furthermore, the effect of snorkel immersion depth (SID) on the circulation rate, mixing time, and fluid flow are investigated. The results indicate that the circulation rate decreases with the increase of SID, while the mixing time shows an uptrend with the increase of SID. Particularly, when the SID exceeds 0.4 m, the scope of dead zone around the snorkel dramatically increases, which further decreases the flow velocity of slag layer in the ladle.
  • Effect of Laminated Structure on Mechanical Properties of Composition-modulated Co–Ni Laminated Plating

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    DOI:10.2355/isijinternational.ISIJINT-2019-293

    A composition-modulated Co–Ni laminated plating has been developed to prolong the lifetime of molds to be employed in continuous steel casting. We have investigated the relationship between the laminated structure and the mechanical properties of the plating films. The tensile strength of as-plated film was enhanced by the thinned thickness of the constituent layers, while the elongation received no effect of the thickness change of the constituent layer and remained almost stable in the range from 3 to 5%. Heat treatment at 400°C have brought about the improvement both in the tensile strength and the elongation. The improvement in the elongation was as remarkable as reached 13% in the film composed of layers with a thickness of 0.8 µm. The layer with low Ni content had an hcp structure, and that with high Ni content produced two phases of the hcp and fcc structures in the as-plated state. By the heat treatment, the high Ni-content layer turned into the single fcc phase, while the low Ni-content layer kept the hcp phase, and accordingly, the film structure changed into the one where the lamination of the hcp and fcc layers was distinct. The fact that the fcc layers, which was easily deformed, were formed continuously in the lateral direction, was seemed to contribute to the significant improvement in the elongation after heat treatment.
  • Enhancement of Mechanical Properties of AISI304 Stainless Thin Plate by Low-pressure, Repeated Explosive Hardening

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    DOI:10.2355/isijinternational.ISIJINT-2019-057

    In order to improve the mechanical properties of AISI304 stainless thin plate, a low-pressure, repeated explosive hardening process was carried out using the explosive treatment technique. Both the residual microstructures and mechanical properties of the treated material were investigated and compared with the undeformed sample. The results show that microhardness, yield strength and ultimate strength of the treated sample remarkably enhanced during a low-pressure, repeated explosive hardening. We propose that the strengthening mechanisms are closely related to the microstructure evolution during the low-pressure, repeated explosive hardening. The corresponding microstructures in the twice hardening samples were dominated by deformation twins, α martensites, with a few deformation bands. The microstructures in the four times hardening samples were characterized by deformation bands and α martensites, where volume fraction of martensite was larger than that in the twice hardening sample.
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    1. Observation of Deadman Samples in a Dissected Blast Furnace Hearth ISIJ International Advance Publication
    2. Analysis of the Coke Particle Size Distribution and Porosity of Deadman Based on Blast Furnace Hearth Dissection ISIJ International Advance Publication
  • Observation of Deadman Samples in a Dissected Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2019-244

    The actual state and packing condition of deadman in blast furnace (BF) hearth have always been a matter of great concern. For it directly affects thermal state of BF hearth and relates to the smooth operation and longevity of BF. In this study, a commercial BF was dissected and then core drilling and image processing methods were used to obtain typical samples and characteristics of deadman. The results show that the deadman, with a radius of 80.09% of hearth radius, floated in hearth and surrounded by molten iron. The sample in horizontal direction has an average coke size of 28.04 mm and a void fraction of 0.52 while the vertical sample has an average coke size of 30.55 mm and a void fraction of 0.50. It should be noted that the average diameter of coke is the reference value which will be different depending on different assumptions. The coke size of vertical sample shows decreasing trendfrom topside to middle part and then keeps slight fluctuations.. And the void fraction in the middle of the vertical sample is the largest and gradually decreases toward both the upper and lower ends. Changes in these features of deadman are caused by the renewal of deadman and the flow of molten iron.
  • Shrinkage Distribution of Sintering Bed Evaluated by X-ray CT Observation

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    DOI:10.2355/isijinternational.ISIJINT-2018-687

    Increasing sinter productivity, product yield, and sinter strength are important for more efficient processes. Because the sintering bed structure should strongly affect such sintering performances, evaluation techniques and controlling methods have been studied. X-ray computed tomography (CT) was used in several studies, because a sintering bed can be observed without destroying it. Sintering bed shrinkage has been also focused on as an index of product yield or sinter strength, because shrinkage should indicate structural change of the sintering bed. However, shrinkage was only evaluated as a cumulative value at the end of sintering, and material behaviour in the sintering bed has not been clarified. In this study, the correlation of shrinkage and sintering bed structure by X-ray CT observation was investigated. Tracers were located in the sintering bed, and the vertical shrinkage distribution was derived from their height change. The result was compared with the shrinkage change with time. Several factors for shrinkage were considered, and their influence degree was discussed. The main factor was sintering with melt formation. This result, however, contradicted the positive effect of ‘stand', which prevents shrinkage and improves productivity and product yield. The reason is discussed, focusing on the support effect of the stand and difference in shrinkage distribution in the sintering bed. A quench test at a certain time during sintering was also carried out, and the transition state from granule to sinter was evaluated.
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    1. Reaction Behavior of Coke in a High Alumina Slag ISIJ International Advance Publication
    2. Formulation of Shrinkage Rate of Sinter During Softening Process Tetsu-to-Hagané Vol.105(2019), No.8
    3. Accuracy Evaluation of Phase-field Models for Grain Growth Simulation with Anisotropic Grain Boundary Properties ISIJ International Advance Publication
  • Fabrication of Ultrafine Grained High Speed Steel with Satisfactory Carbide Dissolution by Electropulsing Treatment

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    DOI:10.2355/isijinternational.ISIJINT-2018-774

    Microstructure of M2 high speed steel (HSS) after electropulsing treatment (EPT) was studied. The secondary carbides precipitated during pre-tempering were dissolved completely during EPT. But the secondary carbides in the starting microstructure cannot be dissolved completely upon conventional reheating to the temperature same as that during EPT. The austenite grain size was ultra-refined by EPT. This study provides a new way to refine austenite grain size in HSS without diminishing the dissolution amount of carbides.
  • Dendrite Segregation Changes in High Temperature Homogenization Process of As-cast H13 Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-148

    The microstructural evolution and microhardness changes of the H13 ingot during homogenization process were investigated to characterize the dendrite segregation changes by optical microscopy (OM), scanning electron microscopy (SEM), electronic probe micro-analyzer (EPMA), X-Ray diffraction (XRD) and microhardness testing. The results showed that the severe dendrite segregation existed in H13 ingot, and there were a large amount of coarse non-equilibrium eutectic carbides (MC and M7C3) in dendrite region. After the soaking time of 15 h at 1200°C, the dendrites almost disappeared, the contents of eutectic carbides decreased sharply. The values of segregation ratio SR were 1.20 for Cr, 1.26 for Mo and 1.41 for V, which were the critical values of SR that marked the end of homogenization. After 20 h, a small amount of MC carbides still distributed at the grain boundaries. The SR values almost remained constant with the values of 1.10, 1.14 and 1.14 for Cr, Mo and V element respectively. The homogenization kinetics was established and it matched well with the experimental data. The microhardess in different soaking time reflected well the dendrite segregation changes, it decreased from 817.8 HV to 645.7 HV and then increases to 752.5 HV, finally it decreases gradually.
  • Analysis of the Coke Particle Size Distribution and Porosity of Deadman Based on Blast Furnace Hearth Dissection

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    DOI:10.2355/isijinternational.ISIJINT-2019-253

    Changes in particle size distribution, mineral yield and strength of coke samples from various locations of two Chinese blast furnaces as well as deadman porosity were investigated in the present study for an in-depth understanding about the blast furnace hearth phenomenon. It was found that the percentage of <10 mm coke fines varied from 20% to 49% in majority of the hearth-level regions. The average size of hearth coke was about 20 mm–31 mm. Compared with the feed coke, the hearth coke size was observed to decrease by 43%–63%. The average size of hearth coke particles of a 2800 m3 blast furnace in diameter direction distributed in "M-shape" in majority of the hearth-level regions while that of a 5500 m3 blast furnace distributed in inversed "V-shape". The hearth coke mass was 1.43–2.21 times of the feed coke under the same conditions. The M10 of hearth coke with size larger than 40 mm after drum test was about 11%–18% and the M40 was 75%–79%. The M10 increased with the increasing distance to the tuyere level while the M40 decreased with the distance. Due to the catalytic effect of hot metal on coke graphitization, the M10 of hearth coke in the lower part was increased by 63.6% compared with the coke in the upper part. The average porosity of the edge, the middle and the center areas was 0.334, 0.299 and 0.250, respectively. The average porosity of deadman decreased with the increase of distance to the center line of the taphole and the increasing distance to the furnace wall.
  • Numerical Analysis on the Performance of COREX CGD Shaft Furnace with Top Gas Recycling

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    DOI:10.2355/isijinternational.ISIJINT-2019-058

    A three-dimensional steady state mathematical model, considering the chemical reactions and the transfers of momentum, heat and mass between the gas and solid phases, is developed to investigate the performance of COREX central-gas-distribution (CGD) shaft furnace with top gas recycling (TGR). The model is validated first by data from practical measurement and then is used to study the performance of CGD shaft furnace with TGR. The results reveal that, compared with the process of 15% CGD gas input without TGR, the TGR can reduce the fresh gas consumption from 1058 Nm3/tBurden to 392 Nm3/tBurden. The reduction potential of top gas with TGR increases from 0.5755 to 0.6293, the utilization rate of top gas decreases from 34.18% to 28.03%, the metallization rate of solid product increases from 61.80% to 70.05%, and the standard deviation of metallization rate decreases from 0.8% to 0.4%.
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    1. Analysis of the Coke Particle Size Distribution and Porosity of Deadman Based on Blast Furnace Hearth Dissection ISIJ International Advance Publication
  • Effects of Fine Precipitates on Austenite Grain Refinement of Micro-alloyed Steel during Cyclic Heat Treatment

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    DOI:10.2355/isijinternational.ISIJINT-2019-153

    The effects of fine precipitates on the austenite grain refinement of micro-alloyed steel during cyclic heat treatment were investigated under different solution treatments. After three rounds of cyclic heat treatment of Ac3 and Ar3 transformations of the as-received steel rod with rapid heating and cooling, the austenite grain size was 3–10 μm. On the other hand, three rounds of cyclic heat treatment after solution treatment at 1300°C reduced the austenite grain size to 2–5 μm. The as-received sample included AlN–Ti(C,N)–MnS composite particles with a mean diameter of 30 nm and a number density of 11 μm-3, and the mean diameter did not change during cyclic heat treatment. Thus, it was considered that the reduction in austenite grain size without solution treatment was caused by the increase in the nucleation site of austenite phase with increasing number of cycles, due to the refinement of the prior austenite grains with martensitic structure during the cyclic heat treatment. When solution-treated at 1300°C, the AlN–Ti(C,N)–MnS composite particles were solved, and they were precipitated during the cyclic heat treatment with a mean diameter of 12 nm and an increased number density of 85 μm-3. Thus, it was considered that the further reduction in austenite grain size with solution treatment was caused by the pinning effect of the fine precipitates, in addition to the increase in the number of austenite phase nucleation sites with increasing number of heat treatment cycles.
  • Effects of Process Conditions, Material Properties, and Initial Shape of Flaw on the Deformation Behavior of Surface Flaw during Wire Drawing

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    DOI:10.2355/isijinternational.ISIJINT-2019-196

    The effects of process conditions, material properties, and initial shape of flaw on the deformation behavior of surface flaw during wire drawing process have been investigated to understand the deformation behavior of surface flaw and to find solutions to decrease them using the finite element (FE) analysis. The surface flaw decreased with decreasing die angle and friction coefficient, and with increasing reduction of area (RA) per pass. Interestingly, the surface flaw and strain inhomogeneity of wire rod were simultaneously decreased at the same process conditions. The shape of surface flaw was somewhat varied with strain hardening exponent (n) and almost same regardless of strain hardening coefficient (K), which means the effect of material properties such as K and n values is not critical. The higher flaw angle has a positive effect on removing or reducing the surface flaws during wire drawing process. The V shape surface flaw in wire rod was relatively well removed; whereas, U shape flaw tends to deform in the manner of overlap with increasing total RA, which means U shape surface flaw was much more detrimental than V shape flaw. To reduce or remove the surface flaw during wire drawing, homogeneous plastic deformation along the radial direction was necessary. Based on above results, seven strategies were proposed to remove or reduce the surface flaw of wire rod during wire drawing process, which can be helpful in determining the guideline to design the wire drawing process.
  • Fatigue Strength Improvement by Replacing Welded Joints with Ductile Cast Iron Joints

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    DOI:10.2355/isijinternational.ISIJINT-2019-237

    In this study fatigue experiments are conducted for ductile cast iron (DCI) to compare with the fatigue strength of cruciform welded joints. Here, several DCI specimens are prepared to have nearly the same fatigue strength in smooth specimens before welding and to have similar cruciform shapes in the welded joints. It is found that the fatigue strength of DCI specimen is about three times larger than that of the welded joint specimens. The fatigue strength improvement can be explained in terms of the small stress concentration factor, notch insensitivity and compressive residual stress generated by shot blasting for DCI joints.
  • Formation Mechanism of Oxide Inclusions in Cr–Mn–Ni Stainless Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-806

    The evolution mechanism of oxide inclusions in Cr-Mn-Ni stainless steel was investigated by industrial trials and thermodynamic calculation. The morphology, composition, and size distribution of inclusions in steel specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. During the LF refining process, there were mainly liquid Ca–Si–Mg–Al–O inclusions in molten steel deoxidized with FeSi alloy. Combined with the Al–Si–O phase diagram, the specimen compositions were also located in the liquid oxide phase. At the same Al content, increasing Si content could make the steel compositions in the liquid oxide phase to avoid the formation of Al2O3. After continuous casting, the number density of Ca–Si–Mg–Al–O inclusions decreased to 1.81 mm-2. On the contrary, the number density of Mn–(Al–Ti)–O inclusions increased to 4.62 mm-2. The MnO contents of most Mn–(Al–Ti)–O inclusions were higher than 40%. The size of most Mn–(Al–Ti)–O inclusions was smaller than 3 µm. The formation of these inclusions was consistent with thermodynamic calculation, which indicated that Mn–Al–O and Mn–Ti–O inclusions were formed during the solidification of Cr–Mn–Ni stainless steel. The effects of different Al and Ti contents on the formation of oxide inclusions during continuous casting process were discussed.
  • Contribution of Mineralogical Phases on Alkaline Dissolution Behavior of Steelmaking Slag

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    DOI:10.2355/isijinternational.ISIJINT-2019-049

    To suppress alkaline elution from steelmaking slag through microstructure control, in this study, several mineralogical phases identified in industrial steelmaking slag were synthesized, and their dissolution behaviors were investigated. The results indicated that in addition to free CaO and free MgO, 2CaO·SiO2-3CaO·P2O5 (C2S–C3P) is another reason for alkaline elution from steelmaking. To suppress the amount of C2S–C3P in steelmaking slag, reducing the slag basicity by the compositional modification of slag at the hot stage was considered. To determine the optimum composition, the contribution of newly formed primary crystalline phases must be clarified. Some primary crystalline phases in the CaO–SiO2–FeOx–MgO–Al2O3 system were synthesized, and their dissolution behaviors were evaluated. The results indicated that the formation of α-CaO·SiO2 (α-CS), β-CaO·SiO2 (β-CS), 3CaO·2SiO2 (C3S2), 2CaO·MgO·2SiO2 (C2MS2), and 3CaO·MgO·2SiO2 (C3MS2) must be restrained in slag modification. Based on the results, a slag with multiple components and low basicity was synthesized, and the suppression of alkaline elution by reduction of slag basicity and microstructure control was confirmed. Moreover, a method to predict Ca dissolution and pH change during the dissolution of slag by the combination of each crystal phase was proposed.
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    1. Formation Mechanism of Oxide Inclusions in Cr–Mn–Ni Stainless Steel ISIJ International Advance Publication
  • Effect of Coordination Structure of Iron Ions on Iron Oxide Activities in Na2O–SiO2–FeO–Fe2O3 Melts

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    DOI:10.2355/isijinternational.ISIJINT-2019-097

    Activities of FeO and FeO1.5 in Na2O–SiO2–FeO–Fe2O3 melts have been investigated in terms of the coordination structure of iron ions. The melts were placed in Pt containers at 1573 K and equilibrated at partial pressures of oxygen in the range between 10-9 atm and 10-6 atm, and the activities were derived from Fe concentrations in the Pt containers using the activity coefficient of Fe in Pt–Fe alloys reported as a function of molar fraction of Fe. At the same time, the percentages of Fe2+, Fe3+ in octahedral symmetry (Fe3+(oct)) and Fe3+ in tetrahedral symmetry (Fe3+(tetr)) were also measured by Mössbauer spectroscopy. It has been found that the activity coefficients of FeO (γFeO) are larger than those of FeO1.5 (γFeO1.5), suggesting that FeO is prone to liberate from the silicate network more than FeO1.5. It has also been found that the values of γFeO monotonically increase with increasing Fe2+/Fetotal ratio; in contrast, the values of γ FeO1.5 seem relevant to neither Fe3+(oct)/Fetotal nor Fe3+(tetr)/Fetotal ratio. The activity coefficients have been discussed from the perspective of the coordination structure via the effective ionic radii of Fe2+, Fe3+(oct) and Fe3+(tetr). The magnitude of effective ionic radii is in the hierarchy of Fe2+ > Fe3+(oct) > Fe3+(tetr), and thereby the bond strength between iron ion and oxide ion is in the hierarchy of Fe3+(tetr) > Fe3+(oct) > Fe2+. This suggests that Fe2+ ions are more loosely bound to the silicate skeleton than Fe3+(tetr) and Fe3+(oct) ions, which situation would be reflected in the magnitude of the activity coefficients and their dependencies on Fe2+/Fetotal, Fe3+(oct)/Fetotal and Fe3+(tetr)/Fetotal ratios.
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    1. Comparison between the Capability of MgO and that of TiN on the Heterogeneous Nucleation of δ-Fe Containing 0.05 mass%C Tetsu-to-Hagané Vol.105(2019), No.8
  • Numerical Simulation of Collision-Coalescence and Removal of Inclusion in Tundish with Channel Type Induction Heating

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    DOI:10.2355/isijinternational.ISIJINT-2019-118

    Numerical simulation is an effective tool to analyze the inclusion behavior in the tundish with channel induction heating. And the inclusion mass/population conservation model is applied to predict and describe inclusion physical field. Due to the channel induction heating, Archimedes slipping velocity and Archimedes collision are applied to describe the inclusion behavior in the tundish with channel induction heating. The predicted values agree with the experimental data for the inclusion model. Numerical results show that Joule heat and electromagnetic force can prompt the inclusion removal rate. Compared with Joule heat, electromagnetic force is a more important factor to affect the inclusion's movement and Archimedes collision is also one of the important collision mechanisms for inclusion coalescence. The inclusion removal rate in the channels is up to one third of the inclusion removal rate in the tundish, and the inclusion removal rate in the tundish increases from 21.4% to 35.05% if channel induction heating is applied.
  • Corrosion Behavior of Alumina Containing Refractory in Blast Furnace Hearth by CaO–SiO2–MgO–Al2O3–Cr2O3 System Slags

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    DOI:10.2355/isijinternational.ISIJINT-2019-149

    The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO–SiO2–MgO–Al2O3–Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.
  • Sensitization and Self-healing in Austenitic Stainless Steel: Quantitative Prediction Considering Carbide Nucleation and Growth

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    DOI:10.2355/isijinternational.ISIJINT-2019-264

    The degree of sensitization in an austenitic stainless steel, has been measured using double loop electrochemical reactivation tests, and the measured values compared with predictions based on grain boundary chromium depletion characteristics obtained using the precipitation and diffusion modules of Thermo-Calc. In order to quantitatively predict Cr depletion, the precipitation of M23C6 carbides that are responsible for sensitization has been modelled for isothermal conditions by treating nucleation and growth separately. Based on a critical chromium concentration, a depletion parameter that predicts both sensitization and self-healing is given.
  • Effect of CaO–MgO–SiO2–Al2O3–TiO2–CaF2 Slag Composition on Inclusions in Ti-Stabilized 20Cr Stainless Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-277

    Laboratory experiments and thermodynamic calculation for the Al-killed Ti-stabilized 20Cr stainless steel with several CaO–MgO–SiO2–Al2O3–TiO2–CaF2 slags containing different CaF2 contents were performed to investigate the effect of slag composition on inclusions in molten steel. The titanium and magnesium contents were higher in the steel samples reacted with the slag samples containing higher CaF2 contents. The thermodynamic results based on the ion and molecule coexistence theory (IMCT) also indicated that the log (a2SiO2/aTiO2), log(a2Al2O3/a3TiO2) and log(aAl2O3/a3MgO) decrease with the increase of CaF2 content in slag, which would make the molten steels have higher titanium and magnesium content. The increase of magnesium content in steel due to the increase of CaF2 in slag led to the increase of MgO content of inclusions. Due to the highest CaF2 content in slag, some inclusions in the steel were located in (liquid + MgO + TiSp) phase field. Reducing the CaF2 content in slag to 5.18 mass%, the MgO content of inclusions in steel was reduced, which made most of the inclusions located in or close to liquid oxide phase field. The reasonable CaF2 content in slag was discussed with the consideration of controlling the titanium content and the formation of inclusions in molten steel.
  • Applicability of Time-Gated Raman Spectroscopy in the Characterisation of Calcium-Aluminate Inclusions

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    DOI:10.2355/isijinternational.ISIJINT-2019-122

    Calcium aluminate (CaO–Al2O3) phases play a critical role in the study of non-metallic inclusions in aluminium killed, and calcium treated steels. In this study, the Raman spectroscopy technique, a versatile and non-destructive approach, was used to characterise binary calcium aluminate phases qualitatively and quantitatively. Calcium aluminate samples with varying CaO/Al2O3 ratios were synthesised to produce a binary phase samples mixture of C12A7–C3A and C12A7–CA. Quantitative estimation was based on plotting a linear regression calibration model between the ratio of Raman band intensities and the phase fraction in the samples. With the linear regression, the phase fraction of C12A7–C3A and C12A7–CA was estimated with average absolute errors of 2.97 and 2.55 percentage points. This work demonstrates the potential suitability of using Raman spectroscopy technique for evaluating whether calcium aluminate phases in oxide inclusions fall within the liquidus region at steelmaking temperatures.
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  • Coke Microstructure and Graphitization Across the Hearth Deadman Regions in a Commercial Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2019-004

    Changes in porosity and graphitization degree of coke samples passing through different locations in the hearth deadman of a commercial blast furnace were investigated. SEM-EDS and Raman spectra were used to measure the coke microstructure and carbon structure. It indicates that the final slag migrate into the coke matrix and react with the minerals in the coke, resulting in the various conditions of the compositions of coke minerals. Al2O3 content in the coke matrix is higher compared with the final slag. With the deadman coke downward, the basicity of the slag increases firstly and then decreases. Si particles with diameter of about 30 um are deposited in the coke pores and different shaped Fe3Si are found in the deadman coke. The porosity of coke shows a liner relationship with coke descending. The porosity of coke above the taphole centerline is 27.74%. It is 33.72% near the taphole centerline and is with 42.47% below the taphole centerline. The structure as well as graphitization of deadman coke indicates higher ordering of coke below the taphole centerline regions than that of the other two samples. These results have an important practical significance for the dissolution reaction of coke in the blast furnace hearth.
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    1. Formation of Hematite Whiskers during Magnetite Concentrate Oxidation ISIJ International Advance Publication
  • Grain Size Effect on the Nitrogen Super-Saturation Process into AISI316 at 623 K

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    DOI:10.2355/isijinternational.ISIJINT-2019-069

    Coarse and fine grained AISI316 substrates were prepared to describe the grain size effect on the inner nitriding behavior at 623 K by using the high density plasma nitriding without precipitation of nitrides. In case of coarse grained AISI316, the nitriding process advanced homogeneously in one part of nitrided layer with high nitrogen content, and, heterogeneously in its other part. In the former, γα' two-phase, fine microstructure was uniformly formed by the phase transformation and plastic straining with the nitrogen supersaturation. In the latter, the nitrogen super-saturation localized to selectively modify the coarse grains to form the transformed α'-phase zones with the plastically strained γ-phase ones, even below the nitriding front end of 30 μm. In case of fine-grained AISI316, the nitriding took place homogeneously to form fine, two-phase microstructure down to the nitriding front end of 40 μm. This difference in the inner nitriding behavior came from the synergetic relationship between the nitrogen diffusion and super-saturation processes.
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    1. Effect of Substitutional Element Addition on Hall-Petch Relationship in Interstitial Free Ferritic Steels ISIJ International Advance Publication
  • Optimization of Measuring Parameters for Two-dimensional Elemental Mapping in Laser-induced Breakdown Optical Emission Spectrometry Using 1-kHz Q-switched Nd:YAG Laser

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    DOI:10.2355/isijinternational.ISIJINT-2019-088

    This paper described how the lateral resolution of an elemental mapping was estimated in laser-induced breakdown optical emission spectrometry (LIBS), when the focus point of a high-frequency Q-switched Nd: YAG laser was moved on a sample surface, along with measuring the emission signal from the resultant plasma. Several measuring parameters were optimized to improve the lateral resolution; namely, they were an averaged laser power of 1 mJ/pulse, a laser repetition frequency of 1 kHz, a scanning rate of the laser beam of 0.5 mm/s, and an atmospheric gas pressure of He 1000 Pa. Using these optimal parameters, a lateral resolution was obtained to be ca. 20 μm in the one-dimensional direction of laser scan. Furthermore, two model samples, in which regularly-aligned copper circles were deposited on a nickel plate, were irradiated by a scanning laser beam to determine actual resolving abilities both in a line direction along travelling the laser and in a two-dimensional direction over a certain sample area. The sample having an interval of 85 μm between the copper circles could give an emission image which was appropriately resolved in the two-dimensional as well as the one-dimensional direction; however, in the other sample having the 25-μm interval, the two-dimensional resolution became degraded compared to the resolution of the line scan, probably because the ablation grooves, which were left on the sample surface, had a width of more than 100 μm and were overlapped with each other in the observed area.
  • Formation of Hematite Whiskers during Magnetite Concentrate Oxidation

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    DOI:10.2355/isijinternational.ISIJINT-2018-755

    Iron ore pellets prepared from magnetite concentrate are strengthened by oxidation of magnetite to hematite during pellet firing. In the present work, hematite whiskers were observed to grow on the oxidized surface of magnetite concentrate particles, over the entire temperature range studied (800°C to 950°C). The whisker thickness increased from approximately 30 nm for oxidation at 800°C to 200 nm at 950°C. The whiskers likely act as bridges between concentrate particles during pellet firing, contributing to pellet strength.
  • Effect of Substitutional Element Addition on Hall-Petch Relationship in Interstitial Free Ferritic Steels

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    DOI:10.2355/isijinternational.ISIJINT-2019-100

    The effects of individual substitutional element addition (Si, Al, Mn, Cu, Ni and Cr) on Hall-Petch relationship in interstitial free ferritic steels were systematically investigated by employing experimental examinations, the pie-up models and grain boundary segregation theory. Chemistry-dependent Hall-Petch coefficients were observed, which was principally interpreted based on the established correlations between the critical grain boundary shear stress and the grain boundary segregation depending on the kind of elements. Exceeded grain boundary segregation levels were found to be the predominant contributions of enhanced grain refinement strengthening abilities.
  • Insights into Accumulation Behavior of Harmful Elements in Cohesive Zone with Reference to Its Influence on Coke

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    DOI:10.2355/isijinternational.ISIJINT-2019-140

    The accumulation behavior of harmful elements (K, Na, Zn) in the upper area of the cohesive zone was reported for the first time. The alkalis-bearing aluminosilicate minerals and the kalsilite were found in the coke, while a number of zinc oxide crystals mainly existing as hexagonal wurtzite habit and zinc-bearing minerals were observed in the mixture-like phase of slag-iron. The findings further deepen the understanding of degradation behavior of coke in the cohesive zone.
  • Gigacycle Fatigue Fracture of Low Strength Carbon Steel, Tested using a Simulated Heat Affected Zone Microstructure

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    DOI:10.2355/isijinternational.ISIJINT-2019-086

    In this study, gigacycle fatigue properties were investigated for several microstructures prepared by heat treatment designed to simulate the heat-affected zone (HAZ) that results from welding. The results showed that internal matrix crack origin gigacycle fatigue becomes dominant in coarse-grained microstructures in spite of low tensile strength of only about 600 MPa. It was found that, high material strength is not always necessary and that microstructure plays an important role in the development of internal-origin gigacycle fatigue fractures.
  • Behavior of Crystallization on a Continuous Solidification of Blast Furnace Slag

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    DOI:10.2355/isijinternational.ISIJINT-2019-147

    A continuous blast furnace slag solidification process was developed to promote the use of air-cooled slag coarse aggregate for concrete. In this process, molten slag can be solidified in only 120 seconds, and the thickness of the slag is about 25 mm. After crushing the slag, the water absorption ratio is much lower than that achieved in the past because gas generation is suppressed. With this apparatus, most of the slag is crystalline, but part of the slag has a glassy surface. Therefore, EPMA and XRD were used to study the glass transition phenomenon. It found that the thickness of the glass layer is about 2 mm. To discuss the glass transition and crystallization phenomena, the thermal history was simulated by heat transfer analysis. The results clarified the fact that all the slag on the mold has a glassy surface layer of about 2 mm, and good agreement between the calculation and experimental data concerning the layer was obtained. It was also shown that most of the slag crystallizes in the slag pit because the temperature inside the piled slags rises to more than 1173 K. The measured slag temperature and calculated temperature were also in good agreement.
  • Microstructure and Phase of Carbon Brick and Protective Layer of a 2800 m3 Industrial Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2019-029

    In this paper, the residual thickness of carbon brick, residual carbon brick and skull of a Chinese 2800 m3 blast furnace hearth were studied in detail and the formation mechanism of skull and brittle layer were proposed. The results show that the remaining thickness of carbon brick is highly inhomogeneous in the height and circumferential direction. In the circumferential direction, the sidewall erosion in the range of 3.6 m under the taphole is more serious. In the height direction, the carbon brick at the distance of 1.0–2.0 m below the central line of the taphole is more obvious. The erosion of hearth bottom is "mumps face+ bowl" type erosion. The minerals of the hot surface of carbon brick used for more than nine years are mainly composed of KAlSiO4, KAlSi2O6, Zn2SiO4 and ZnO as well as a small amount of ZnS, KCl and ZnAl2O4. Micro cracks resulted from the KAlSiO4, KAlSi2O6, Zn2SiO4 and ZnAl2O4 are the inducement of formation of brittle layer. The main reason for the formation of macro cracks and brittle layer in carbon brick is the continuous accumulation of ZnO in micro cracks. The brittle layer mainly occurs in the region where the temperature of carbon brick is lower than 950°C. The skull above the central line of the taphole is mainly composed of Ca2Al2SiO7, Ca2MgSi2O7, CaTiO3 and KAlSiO4. The skull below the central line of the taphole is primarily comprised of Ca2Al2SiO7, Ca2MgSi2O7, CaS, Fe and Fe3Si. The blast furnace slag phase in the skull below the central line of taphole is derived from the blast furnace slag that penetrates into the deadman coke. The blast furnace slag can be present below the central line of the taphole and adhere to the hot surface of the carbon brick to isolate the direct contact between the molten iron and carbon brick.
  • Recycling of Blast Furnace Sludge to the Blast Furnace via Cold-Bonded Briquettes: Evaluation of Feasibility and Influence on Operation

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    DOI:10.2355/isijinternational.ISIJINT-2019-080

    Ore-based steelmaking generates various residues including dusts, sludges, scales and slags. Recycling of these residues within the process or via other applications is essential for sustainable production of steel. In blast furnace (BF) ironmaking, the gas-cleaning equipment generally recovers the particles in the off-gas as dust and sludge. Traditionally, the dry dust is recycled via the sinter or, in the case of pellet-based BF operation, via cold-bonded briquettes and injection. As the BF sludge mainly consists of iron and carbon, this residue is of interest to recycle together with the BF dust. However, depending on how the BF is operated, these two residues are more or less the major outlet of zinc from the furnace. Thus, to limit the recycled load of zinc, both materials cannot be recycled without dezincing the sludge prior to recycling. Dezincing and recycling of the low-zinc fraction of BF sludge via sinter have been reported whereas recycling via cold-bonded briquettes has not been performed. In the present study, cold-bonded briquettes containing the low-zinc fraction of dezinced BF sludge were charged as basket samples to the LKAB Experimental Blast Furnace (EBF). The excavated basket samples from the quenched EBF suggested that additions of up to 20 wt.% of upgraded BF sludge was feasible in terms of reducibility and strength. Based on these results, BF sludge were added to cold-bonded briquettes and charged in industrial-scale trials. The trials indicated that the annual generation of BF sludge, after dezincing, could be recycled to the BF.
  • Solubility of Sulfur in the Solid Oxide of the Calcium-Aluminate System

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    DOI:10.2355/isijinternational.ISIJINT-2019-127

    The formation of CaS around CaO–Al2O3 causes pitting corrosion in ferritic stainless steel. To prevent the precipitation of CaS, the solubility of CaS in both the liquid and solid CaO–Al2O3 system has to be clarified. In this study, the sulfur content in the CaS-saturated solid CaO–Al2O3 system was measured. The results showed that, sulfur was soluble only in 12CaO·7Al2O3 at approximately 1.2 mass% while the sulfur content in the other solid compounds was very low. In addition, the sulfur content of 12CaO·7Al2O3 was independent of the heating temperature and was higher than that in the liquid oxide of the same composition. Therefore, 12CaO·7Al2O3 can dissolve sulfur in the solid state, preventing CaS formation.

Article Access Ranking

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