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

ISIJ International Advance Publication

  • Internal Friction Behavior Associated with Martensitic Decomposition in Low-carbon Dual-phase Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-718

    In this study, the martensitic decomposition behaviors of a low-carbon dual-phase steel were investigated by the low-frequency internal friction method, combined with various structural analysis techniques including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Two internal friction peaks were observed at 418.4°C and 448.1°C, and were attributed to desolventization of supersaturated carbon atoms from martensite and formation of Cr3C7 precipitates, respectively. The results indicated that the two-step process during the martensitic decomposition, involving carbon atom diffusion and carbide precipitation, could be well explained by the internal friction technique. The microstructural mechanisms associated with the generation of the two internal friction peaks during the martensitic decomposition are discussed.
  • Demystifying Underlying Fluid Mechanics of Gas Stirred Ladle Systems with Top Slag Layer Using Physical Modeling and Mathematical Modeling

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    DOI:10.2355/isijinternational.ISIJINT-2018-797

    Effects of slag layer thickness on the fluid dynamics of liquid steel in gas-stirred ladles by bottom injection of argon was studied through water modeling experiments and numerical simulations. Mixing times increase considerably with thicker slag layers and decrease of gas flow rates. The physical properties of the system have a smaller influence on mixing time. Slag Eye Opening (SEO) area is increased under thin slag layers, increase of gas flow rates, and denser and less viscous slags. The planes close to the metal-slag interface, under the presence of thick slag layers for a given gas flow rate, are split in subregions of small velocities with different orientations making the lower fluid to come close to a stagnant condition. The presence of, either, thick or thin slag layers does not influence the axial velocity along the plume height for a fixed flow rate of gas. The SEO area follows a linear relationship with the square root of the densiometric Froude number based on the slag layer thickness.
  • A New Data-driven Roll Force and Roll Torque Model Based on FEM and Hybrid PSO-ELM for Hot Strip Rolling

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    DOI:10.2355/isijinternational.ISIJINT-2018-846

    In this paper, a new Extreme Learning Machine (ELM) regression model of roll force and roll torque based on data-driven is proposed. The three-dimensional elastic-plastic finite element model (FEM) is established to solve the roll force and roll torque under different parameters (including rolling reduction rate, roll radius, rolling speed, average width of strip, entry temperature of strip). The regression model of ELM optimized by Particle Swarm Optimization (PSO) is established through using the datasets obtained by FEM. The PSO-ELM model prediction values of roll force and roll torque are compared with the single ELM and PSO-SVM model, and the error results of the prediction values are analyzed. The error results fully verify the feasibility and accuracy of the PSO-ELM model proposed. It is found that the new data-drive model of roll force and roll torque is simple in structure and it can make up for the deficiency of traditional mathematical mechanism model in dealing with nonlinear problems. The research result reveals that PSO-ELM method is suitable for parameters prediction and model optimization in strip rolling process.
  • Causes of Particle Trajectory Fluctuation on the Rotating Chute in Circumferential Direction at Bell-less Top with Parallel Type Hoppers

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    DOI:10.2355/isijinternational.ISIJINT-2018-862

    Uneven burden distribution at bell-less top has a negative influence on the smooth operation of blast furnace with parallel type hoppers. Although previous works agreed that the initially oval-shaped particle trajectory on the chute causes the above-mentioned segregation, the subsequent particle trajectory fluctuation against the circumferential direction was still not fully understood. As a result, this work employs both the discrete element method (DEM) simulation and the theoretical model calculation, to quantitatively elucidate the causes of particle fluctuating behaviors on the rotating chute. The consistent results show that, on the one hand, a sine-like particle velocity distribution causes the Coriolis force to have a maximum magnitude around 120 deg while a minimum around 300 deg in the circumferential direction. On the other hand, the alternately sparse and intensive granular flow on the chute causes the particle mass flow rate to present a sine-like result with a maximum rate around 220 deg while a minimum around 60 deg. The superposition of two results contributes to the particle trajectory fluctuation on the rotating chute in the circumferential direction at bell-less top with parallel type hoppers.
  • Characterization of Dislocation Evolution in Cyclically Loaded Austenitic and Ferritic Stainless Steels via XRD Line-profile Analysis

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    DOI:10.2355/isijinternational.ISIJINT-2019-077

    Dislocations in austenitic and ferritic stainless steels (SSs) under cyclic loading were quantitatively evaluated via X-ray diffraction line-profile analysis to determine the relationship between the dislocation density and low-cycle fatigue (LCF) life in both SSs. The dislocation density of the austenitic and ferritic SSs varied linearly with respect to the LCF life in a double-logarithmic graph, with different slopes of the line. The dislocation density normalized by the maximum work hardening for both SSs exhibited a log–log linear relationship with the LCF life. The fraction of screw dislocations in the ferritic SS decreased with decreasing LCF life owing to the easy cross-slip of dislocations. Because of the difficulty of the cross-slip of dislocations in the austenitic SS, the fraction of screw dislocations remained almost constant throughout the LCF life. Analysis of the crystallite size and the dislocation arrangement with respect to the dislocation density under tensile and cyclic loading revealed that the dislocation arrangement for cyclic loading was smaller than that for tensile loading. Thus, the dislocation arrangement was related to the cyclic loading. In the plot of the dislocation evolution versus the number of cycles, two stages were observed in the variation of the dislocation characteristics for both SSs. In the first stage, the dislocation density increased, and the crystallite size decreased. The dislocation arrangement parameter of the ferritic and austenitic SS decreased and remained the same, respectively, in the first stage. In the second stage, the dislocation density, dislocation arrangement parameter, and crystallite size remained constant.
  • Numerical Investigation of Effect of Casting Speed on Flow Characteristics of Molten Steel in Multistrand Tundish

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    DOI:10.2355/isijinternational.ISIJINT-2018-835

    Casting speed is one of the key factors affecting flow characteristics in the tundish. This paper gives a detailed numerical investigation for the effect of casting speed on flow characteristics in a five-strand tundish. Firstly, a quantitative evaluation method of flow characteristics (such as dead region, short-circuit flow and flow uniformity among multiple strands) is proposed. And then, by using the method, the effect of the cases (such as reducing to the same casting speed for each strand, closing one or two strands, etc.) on flow characteristics in the case of reducing throughput is analyzed. The results show that the case of closing strands 2 and 4 has the best flow characteristics, and not only dead region volume is smaller, but also the flow difference among multiple strands is also smaller. Meanwhile, in view of slower flow and bigger dead region near the far-strand of the tundish and large difference for flow characteristics between the far-strand and other strands, the effect of increasing the far-strand's casting speed on improving the overall flow characteristic in the tundish is also analyzed. The results show that, increasing the far-strand's casting speed can significantly reduce dead region proportion and flow difference among multiple strands, and in the case of the same throughput, the short-circuit flow does not change much. In the case of increasing the same throughput, flow characteristics in the tundish for only increasing the far-strand's casting speed are better than that for increasing casting speed of each strand simultaneously.
  • Ensemble Prediction of Tundish Open Eyes Using Artificial Neural Networks

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    DOI:10.2355/isijinternational.ISIJINT-2018-637

    As global steelmakers are feeling the economical pinch, the need for improving quality and quantity using what is already readily available, increases. This gap in achievement can be bridged by innovation and perforation of already existing techniques and methodologies from other fields. Steel quality, an important issue, is often not associated with a phenomenon known as tundish open eyes. However, recently researchers have shown the detrimental effects of reoxidation and the deterioration of the final product (slabs/billets). Understanding the formation of this event, and mitigating the formation will be an important issue to solve. Current models investigating the former have existed largely in the computational fluid dynamics modelling domain. However, the solution for the former, can only provide static recommendations thus are less useful in a dynamic environment. Hence, development of a reliable model which has the ability to "learn on the fly" is very much needed. In the current study, artificial neural network models have been used to predict non-dimensional open eye sizes in the tundish. The dataset has been compiled from previous regression formulations. The performance of the models is determined based on the following metrics 1) coefficient of multiple determination (R2), 2) and root mean square error (RMSE). The ANN based models, show significant promise, in particular the ensemble variants, which have shown increased accuracy and stability across all domain and range.
  • Mechanism of Pore Formation in Novel Porous Permeable Ceramics Prepared from Steel Slag and Bauxite Tailings

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    DOI:10.2355/isijinternational.ISIJINT-2018-782

    Porous permeable ceramics (PPC) were prepared from composite ceramsites (CC) via a single firing process. CC were granulated with steel slag as a core and bauxite tailings in an outer-layer. XRD, SEM, EDS, mercury porosimetry and metallographic microscopy were used to study its properties and the pore formation mechanism. Results showed that during sintering process, gradual diffusion of cations from slag to tailings layers enhanced bonding among CC with formation of new crystals: anorthite and pyroxene. PPC had a wider distribution of pores from 0–300 µm sintered at 1160°C. With an increase in sintering temperature, ceramics were densified with disappearance of the small pores, which had an increasing threshold diameter values from 45 µm at 1180°C to 70 µm at 1190°C. Big pores larger than the threshold values would be remained and enlarged due to shrinkage of CC during the densification process. The decreasing amounts of pores and an increasing pore diameter had contrary effects on its permeable properties. PPC sintered at 1180°C with porosity of 27.5% and medium pore diameter of 92.7 µm had the optimum properties with bending strength of 10.92 MPa, water permeability of 0.039 cm/s and qualified leaching properties of harmful elements (Mn, Cr, V and Pb). This study would promote a more feasible and economic method for producing porous permeable ceramics and improving added value of steel slag and tailings.
  • Advances in Ladle Shroud as A Functional Device in Tundish Metallurgy: A Review

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    DOI:10.2355/isijinternational.ISIJINT-2019-044

    Ladle shroud is a small but significant device in tundish metallurgy to facilitate both production process and steel quality. Past decades have witnessed its evolution from a simply shrouding tube to a multi-functional device in continuous casting processes. Advances in the functions of ladle shroud in tundish metallurgy have been reviewed in this work, including shrouding the teeming stream, fluid flow control, slag carry-over detection, and the potentials of heating and additive feeding. The features of various commercialized and novel ladle shrouds are discussed. The effect of practical operations, such as argon injection and misalignment, on the performance of ladle shrouds is also analyzed in this review.
  • Effect of Ultra-high Magnesium on SKS51 Liquid Steel Cleanliness and Microstructure

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    DOI:10.2355/isijinternational.ISIJINT-2018-804

    This study emphasizes that ultra-high Mg ([%Mg]>0.03) content is very difficult to be achieved under conventional smelting conditions. The content of Mg in steel has significant influence on the cleanness of molten steel and microstructure. As the content of Mg increases, the content of O and S in steel decreases significantly, with O content as low as 0.0002% and S content as low as 0.0008%. Almost all inclusions in ultra-high Mg steel are magnesium-bearing oxide, sulfide, even carbide. As the content of Mg increases, the number of inclusions in the steel increases and the size decreases. But if too much Mg is added into the steel, the size and number of inclusions will rapid increase. The as-cast secondary dendrite spacing of steel decreased obviously with the increase of Mg content in steel. As the content of Mg increases, the as-cast microstructure changes from lamellar pearlite to granular pearlite. The phase diagram of SKS51 steel was calculated by Thermal-calc software. The calculated results showed that MgC2 was precipitated in the austenite before the austenite was converted into perlite. MgC2 may become the nuclear core, leading to perlite transformation. Suspected MgC2 was found in spheroidized annealing Fe3C core.
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  • Mathematical Modeling of Flow and Heat Transfer Behavior of Liquid Slag in Continuous Casting Mold with Argon Blowing

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    DOI:10.2355/isijinternational.ISIJINT-2018-832

    The bubbles generated by argon blowing in a nozzle have important effects on the flow and heat transfer behavior of mold slag. To determine the effect of argon blowing on the flow and heat transfer behavior of liquid slag in the mold, we developed three-dimensional mathematical models coupled the volume of fluid and discrete phase models. The results showed a small circulation flow of liquid mold slag occurred near the nozzle side face and the mold narrow face respectively at the center plane between the mold wide faces. Additionally, we identified a larger circulation of liquid mold slag in the middle region of the mold. With increased argon flow rate, the flow velocity peak at the liquid steel and slag interface decreased, the temperature of the liquid mold slag increased. A moderate flow rate of argon improved the uniformity of flow velocity and temperature distribution of liquid slag and reduced the flow velocity peak at the interface of the liquid steel and slag. To avoid the solidification of liquid steel at the steel-slag interface near the mold face, moderately high casting speed and argon flow rate and larger inclination angle and immersion depth of the submerged entry nozzle may be beneficial. These results provide a theoretical basis to optimize the parameters of the argon blowing process and improve slab quality.
  • Effect of Coke Particle Arrangement on Reduction and Gasification Reaction in Mixed Layer of Ore and Coke

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    DOI:10.2355/isijinternational.ISIJINT-2019-011

    To reduce CO2 emissions from steel works, low reducing agent rate (low coke rate) operation of the blast furnace is desired. Mixing nut coke in the ore layer is one effective measure for realizing this type of operation. Therefore, the effect of coke mixing on the reduction reaction rate of ore and the gasification reaction rate of coke in the mixed layer of ore and coke was investigated. The reduction rate of the ore and the gasification rate of the coke in the mixed layer of ore and coke was estimated by a reduction and gasification experiment, and the packing structure of the coke in the mixed layer was estimated by a mathematical model analysis using the discrete element method. The reduction rate of the ore and the gasification rate of the coke in the mixed layer was affected by the degree of contact between the ore and coke. In addition, the reduction rate of the ore and the gasification rate of the coke in the mixed layer was accelerated by the effects of mutual utilization of the gases generated by the reactions.
  • Relationship between Alloy Element and Weld Solidification Cracking Susceptibility of Austenitic Stainless Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-035

    The effect of alloy elements such as niobium, titanium, and zirconium on the weld solidification cracking susceptibility in fully austenitic stainless steel was investigated. Niobium, titanium, or zirconium was added as an alloy element to Fe-24 mass%Cr-26 mass%Ni stainless steel. The cracking susceptibility was evaluated by crack length, number of cracks, and brittle temperature range (BTR) corresponding to results of the Trans-Varestraint test. Depending on the addition of the alloy element, the crack length increased; the length ordering tendencies between the total crack length (TCL) and the maximum crack length (MCL) differed with the alloy addition. The BTR was obtained by corresponding the MCL to the temperature range using the measured temperature history of the weld metal and was increased by the addition of the alloy element. The maximum BTR for the specimen with titanium was 266.9°C, which was three times that of the specimen without the alloy element. The MC carbide and the Laves phase formed at the dendrite cell boundaries as secondary phases. Solidification calculation based on the Scheil model was used to investigate the effect of the type of the alloy element on the solidification temperature range. Depending on the type of the alloy element, the solidification temperature range varied. A significant difference was found between the solidification temperature range and BTR in the case of the specimen with niobium.
  • Velocity Characteristics of Air-mist Jet during Secondary Cooling of Continuous Casting Using PIV and LDV

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    DOI:10.2355/isijinternational.ISIJINT-2018-735

    Air-mist jet is increasing in number of facilities for a variety of applications in surface cooling. It can provide a good balance of high heat removal capability. The present study focused on the velocity characteristics of the air-mist jet produced by a fan-shaped nozzle under different operating conditions during secondary cooling of continuous casting. To this end, the authors conducted experimental research, employing optical techniques, i.e., particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) to measure a fanlike flow field in an air-mist jet. However, the researchers observed different results between the PIV and LDV measurements, mainly at the outlet of the nozzle region. This article identifies velocity characteristics of air-mist jet during secondary cooling of continuous casting, which is divided into two parts for velocity distribution structure of air-mist jet, and self-similar and well described by a Gaussian distribution for the whole flow field. The study provides a suggestion to optimise the flow field of a fanlike air-mist nozzle for different working conditions. Furthermore, the behavior of gas-liquid two-phase flow can be understood by examining the difference in velocity characteristics between the PIV and LDV measurements of the air-mist jet.
  • Effects of CeO2 on Melting Temperature, Viscosity, and Structure of CaF2-bearing and B2O3-containing Mold Fluxes for Casting Rare Earth Alloy Heavy Rail Steels

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    DOI:10.2355/isijinternational.ISIJINT-2018-760

    Rare earth have been widely used in the heavy rail steels to improve the impact toughness, yield strength, and high-temperature plasticity by deforming inclusions and refining grains. However, amounts of rare earth oxides with high melting temperatures can be generated and enter the mold fluxes, which has a significant influence on the lubrication and the heat transfer capability of mold fluxes and even the smooth of the continuous casting process. Thus in this work, effects of different CeO2 contents on melting temperature, viscosity, and structure of the CaF2-bearing mold fluxes and the B2O3-containing mold fluxes for casting the rare earth alloy heavy rail steels were investigated systemically. Besides, the mechanisms of the viscosity and structure were discussed. Results show that CeO2 increases the melting temperature and decreases the viscosity at high temperature of both two mold fluxes. The break temperature of the CaF2-bearing mold fluxes increases heavily with the addition of CeO2. Analyses of Raman spectra and the 11B magic angle spinning nuclear magnetic resonance spectra (11B MAS NMR) show that CeO2 enhances the de-polymerization of the network structure of two mold fluxes, leading to the decrease of viscosity at each temperature.
  • Void Nucleation, and Growth during Tensile Deformation of Nanoscale Precipitated Steel and Bainitic Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-762

    A local elongation of 8% for nanoscale precipitated steel was observed via tensile testing, which is higher than that of 5% for bainitic steel. To determine the factor underlying this difference, void nucleation, growth, and coalescence mechanisms in the nanoscale precipitated steel and the bainitic steel were examined using electron backscattering diffraction and subsequent observation by synchrotron radiation X-ray laminography during tensile testing. Synchrotron radiation X-ray laminography analysis of void growth and coalescence revealed that the critical strain and the critical void volume fraction for fracture in the bainitic steel were smaller than those for the nanoscale precipitated steel. Secondary-ion mass spectrometry analyses revealed that C atoms were segregated at grain boundaries in the bainitic steel. Void nucleation sites in the nanoscale precipitated steel were nanoscale precipitates inside the grain and at grain boundaries and coarse precipitates; however, in the bainitic steel, void nucleation sites were entirely at grain boundaries. Nanoindentation hardness measurements showed a larger plastic strain gradient between the grain boundary and matrix in the bainitic steel than in the nanoscale precipitated steel. From these results, the high local elongation exhibited by the nanoscale precipitated steel was concluded to be due to the reduced plastic strain gradient with a uniform hardness distribution between the grain boundary and the grain interior.
  • Work Roll Surface Profile Design and Optimization for Hot-core Heavy Reduction Rolling Process

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    DOI:10.2355/isijinternational.ISIJINT-2018-809

    Hot-core Heavy Reduction Rolling (HHR2) is an innovative technology designed for eliminating center defects of blooms, which provides heavy reduction to blooms with two-high mill after solidification at the end of the strand. This works mainly focus on design and optimization of work roll profile that apply specifically to HHR2 process to obtain the best effect on shrinkage closing. Firstly, hot rolling experiment and corresponding finite element calculation were carried out. Based on the experiment and FEM results, the void closure model was established to describe the behavior of shrinkage closing. Secondly, this model was used in analyzing the effects of different roll profiles on void closure during HHR2 process. The result shows that the convex profile and box groove profile had better effects than flat profile and parabolic profile, which can provide greater value of effective strain and smaller value of stress triaxiality respectively. Finally, a new roll profile for HHR2 was designed by combining both geometrical features of convex profile and box groove profile. The rational value scope of convex width coefficient θ and convex height coefficient γ were optimized to achieve a better effect on eliminating shrinkage cavities.
  • Effect of Pearlite Volume Fraction on Two-step Ductile to Brittle Transition in Ferrite + Pearlite Structure Steel Sheets

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    DOI:10.2355/isijinternational.ISIJINT-2018-764

    Multi structural steels exhibit high strength and good formability; however, their performance depends on the volume fraction of the secondary phase. In our previous study, ferrite + pearlite structural steel sheet showed the characteristic two-step ductile-to-brittle transition (DBT) with decreasing temperature, and the absorbed energy curve exhibited a distinct middle shelf. In this study, we evaluated the effect of pearlite volume fraction (VP) on the DBT behavior by the Charpy impact test with sub-size specimens. For specimens without pearlite, the absorbed energy directly dropped from the upper shelf to the lower shelf with decreasing temperature. For samples with 2–3% pearlite, the absorbed energy corresponding to the transition temperature range was dispersed between the two shelves, and the transition behavior seemed to be the typical DBT behavior. When VP was increased to 21%, the absorbed energy just above the transition-finish temperature became stable at a middle level between the two shelves; thus, the existence of a distinct middle shelf was confirmed. Although the transition-start temperature increased with increasing VP, VP did not affect the transition-finish temperature and the absorbed energy at the middle shelf. These results were analyzed with a simple model based on the Yoffee diagram.
  • An in situ Study of the Formation of Rare Earth Inclusions in Arsenic High Carbon Steels

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    DOI:10.2355/isijinternational.ISIJINT-2018-853

    The application of rare earths is an effective way to stabilize residual elements in steel, such as As and P, so as to improve the performances of steel products. In situ methods were used to investigate the formation of inclusions and their stability at high temperatures in arsenic high carbon steels with additions of lanthanum. The results show that La2O3 and La2O2S started generating in molten steel and had significant difference of appearances and growth behaviors. La2O3 started with triangular particles and rapidly grew up like crystals; by contrast, La2O2S particles were always spherical or near-spherical and didn't significantly grow up. Arsenic existed as LaAsO4 that turned out to be unstable under high temperatures. LaAsO4 decomposed and As dissolved into the matrix when the temperature was higher than 1200°C. The formation of LaAsO4 during solidification and the dissolution of As into the matrix during heat treatment can effectively avoid the local enrichment of As. Therefore, it is possible to control As distributed uniformly in steel by appropriate heat treatment process.
  • Numerical Simulation of Multiphase Flow and Mixing Behavior in an Industrial Single Snorkel Refining Furnace (SSRF): The Effect of Gas Injection Position and Snorkel Diameter

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    DOI:10.2355/isijinternational.ISIJINT-2018-826

    A three-dimensional mathematical model of an industrial Single Snorkel Refining Furnace (SSRF) was implemented in designed experiments to investigate the influence of injection position and snorkel diameter on mixing efficiency and circulation rate. The discrete phase model–volume of fluid coupled model was employed to describe the argon/steel/slag/air multiphase flow. The expansion behavior of argon bubbles was considered. The results indicated that eccentric injection is greatly beneficial for increasing circulation rate and decreasing mixing time. The effect of snorkel diameter was investigated in light of eccentric plug position. It was found that the oversized and undersized snorkel diameter are not desirable, as it contributes poor mixing at ladle bottom and periphery of snorkel, respectively. An optimum diameter was recommended according to a principle that the stirring energy of plume should be distributed reasonably for achieving homogeneous flow in the whole bath.
  • Non-Isothermal Melt Crystallization Kinetics for CaO–Al2O3–B2O3 F-Free Mould Fluxes

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    DOI:10.2355/isijinternational.ISIJINT-2018-677

    Efforts have been made to develop fluorine-free mould fluxes for the continuous casting of steel process. In this work the crystallization behaviour of fluorine-free mould slags based on the CaO–Al2O3–B2O3 system was investigated by differential scanning calorimeter (DSC) and scanning electron microscopy equipped with energy dispersive spectroscopy(SEM-EDS). The crystallization kinetics for Ca3Al2O6 primary crystals was analysed by combining modified Avrami analysis with Friedman isoconversional method. Avrami parameter n is close to 4 for samples with the ratios w(CaO)/w(Al2O3)=1 and w(CaO)/w(Al2O3)=1.2, indicating a crystallization mechanism of continuous bulk nucleation and 3D crystal growth. The Avrami parameter n for samples with w(CaO)/w(Al2O3)=0.9 is close to 3, indicating instantaneous bulk nucleation and 3D crystal growth. The crystallization rate constant is the highest and half crystallization time is the lowest for the samples with w(CaO)/w(Al2O3)=0.9, indicating the fastest crystallization. In the initial stage, effective activation energies were mainly determined by the undercooling values. In the final stage, kinetic barrier for crystallization could have some influence on crystallization; for the investigated mould fluxes crystallization in the final stage is retarded by increasing w(CaO)/w(Al2O3) ratio. Thus crystallization mechanisms were elucidated and effective activation energy of crystallization for the first crystal which precipitates from melt was determined.
  • Structure Based Viscosity Model for Aluminosilicate Slag

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    DOI:10.2355/isijinternational.ISIJINT-2018-724

    Based on the structure of slag, the revised structure based viscosity model was improved for viscosity prediction of the fully liquid slag in the Al2O3–CaO–MgO–SiO2 quaternary system and its subsystems. Experimental procedures and available data in the literature have been critically reviewed. In this modified model, the oxygen ions bonded with non-compensated Al3+ ions were defined as excess bridge oxygens. The concentration of different types of oxygen ions are calculated and used to express the activation energy. The present model is capable of predicting the viscosities in the Al2O3–CaO–MgO–SiO2 quaternary system and its subsystems over the wide composition and temperature ranges above liquidus within experimental uncertainties; the average of relative errors for this model was found to be 17.97%. CaO has a greater ability to decrease the viscosity than that of MgO in the system without Al2O3 because of the weaker bond strength of CaO. A viscosity maximum occurs for MO–Al2O3–SiO2 (M=Ca or Mg) slag with a fixed SiO2 content. The estimated viscosities decrease with the increase of MgO content, decrease with increasing of the Al2O3/SiO2 ratio at 5 mass% of MgO, and keep almost constant or even slightly increase with the increase of the Al2O3/SiO2 ratio at 10 mass% MgO.
  • Temperature Field Distribution of a Dissected Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-753

    The temperature field distribution of the upper part of a blast furnace (BF) is the result of the combination of charge distribution and gas flow. It is of great significance for both researchers and operators to study the thermal state and the phenomenon of the BF. The graphite box method is used in this study to obtain the temperature field distribution in the upper part of a 125 m3 BF. Graphite boxes with a variety of different melting point metals were loaded into the BF with the charge. And the temperature field distribution was obtained after the boxes were taken out with position and temperature information during the dissection process. The results illustrate that the graphite boxes are unevenly distributed in the BF, which was related to the distribution of BF materials. Furthermore, the temperature field distribution is asymmetric, and the isotherms present an irregular "W" shape, which is caused mainly by the simultaneous development of the edge airflow and the central airflow. Moreover, the shape of the softening and melting zone observed in the dissection process has a good correspondence with the temperature field. We concluded that the deflection of the temperature field and the softening and melting zone is related to the strong gas flow in the direction of No. 3 tuyere, the existence of accretion in the hearth, and the filling of refractory materials in tuyeres before blowing out.
  • Optimization of Flocculation Process to Selectively Separate Iron Minerals from Rejected Iron Ultra Fines of Indian Mines and Minimize Environmental Issue

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    DOI:10.2355/isijinternational.ISIJINT-2018-382

    Indian iron ore mining industry disposes large amount of ultra fines containing high gangue minerals, thereby lead to loss of iron values and environmental pollution. Selective flocculation studies have been thought of for beneficiation of ultra fines. Response of different types of starches to iron ore ultra fines generated by the hydro-cyclone in Joda Iron Ore Washing Plants, Orissa, India has been studied. The starches used are: (i) maize starch (MS), (ii) potato starch (PS) and (iii) causticized potato starch (CPS). The order of selectivity as flocculant towards iron bearing minerals is observed as MS<PS<CPS. This can be attributed to the different C-H chain morphology of the starches. MS has more amylopectin than PS. Amylopectin adsorbed strongly onto all oxides minerals as carbonyl groups attached to C-2 and C-3 atoms of starch form surface complex with surface atom of all oxide minerals whereas amylose has a more adsorption tendency to hematite only. Amylose has less number of end groups than amylopectin, thus exhibiting lesser adsorption density than amylopectin. The selective adsorption characteristics of PS to hematite further improves by modification. Iron content and the iron recovery of the concentrate depend on flocculant dosage as well as settling time. A good concentrate is obtained suitable for pellet feed with Fe content in the concentrate increased from 57.8 mass% to 66.3 mass% and with an iron recovery of 66.5% by this process using CPS as a flocculating agent under optimized conditions. The tailing generated is suitable for building materials like tiles.
  • Dependence of Carbon Concentration and Alloying Elements on the Stability of Iron Carbides

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    DOI:10.2355/isijinternational.ISIJINT-2018-695

    The precipitation of iron carbides is a crucial factor that determines the properties of tempered martensite. However, the effect of alloying elements on the carbon concentration of ε carbide has not yet been clarified. In this work, we studied the effect of alloying elements on the carbon concentration of ε carbide using first-principles calculations and a three-dimensional atom probe. The first-principles calculations showed that ε carbide with a lower carbon concentration tends to form by the inclusion of Si. The carbon concentration in ε carbide measured by the three-dimensional atom probe was consistent with the first-principles calculations.
  • Design and Discrete Element Analysis of Accumulated Material-type Distributing Chute on Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-678

    A new accumulated material-type distributing chute on blast furnace (BF) is designed to prolong the service life of distributing chute on BF according to powder mechanics theory, and a Comparative simulations study between the accumulated material-type distributing chute and smooth-plate straight chute is conducted using discrete element method. Additionally, the influence of shape of transverse ribs in accumulated area and particle size on the impact of chute are discussed. Results show that this type of distributing chute on BF has formed a stable material accumulation under the impact zone of material flow and its material cushion forms a certain thickness, which greatly reduces the impact and abrasion of material flow. The impact force of the material flow on the chute is reduced to 10.1%–17.2%, and the sliding velocity of particles near the bottom plate is reduced to 29.1%–33.4% compared with the smooth-plate straight chute. Therefore, the new accumulated material-type distributing chute has good anti-impact ability and abrasion resistance. Shape of transverse ribs in accumulated area and particle size have a relatively small effect on the impact of chute after discussing.
  • Effect of V2O5 Addition on Oxidation Induration and Swelling Behavior of Chromium-Bearing Vanadium Titanomagnetite Pellets with Simulated Coke Oven Gas Injection into Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-681

    The study discusses the oxidation induration and swelling behavior of chromium-bearing vanadium titanomagnetite pellets (CVTP) with V2O5 additions, and the reduction swelling index (RSI) and compressive strength (CS) of reduced CVTP were investigated with simulated coke oven gas (COG) injection into the blast furnace (BF). The results show that the CS of CVTP decreases and the porosity of CVTP increases with increasing V2O5 additions. The proportion of microsize pore size distribution of CVTP between 0 to 5 µm decreases notably while the pore size distribution between 5 to 30 µm increases with increasing V2O5 additions. The V2O5 mainly exists in the form of V2Ti3O9 and V1.93Cr0.07O3 in CVTP and V2TiO5 in reduced CVTP. The V-bearing spinels on the grain boundaries with fragmentized and prismatic structure restrain the CS of CVTP. The CS of reduced CVTP decreases and RSI increases with increasing V2O5 additions. The V2O5 addition facilitates the aggregation and diffusion of metallic iron particles, and the shape of the metallic iron whiskers transform round dot to prismatic. The pores and intervals enlarge, and thickness of lamellar crystals thickens gradually with increasing V2O5 additions. The study could supply the theoretical and technical basis for the utilization of CVTP and other V-bearing ores with COG recyclable technology.
  • Comprehensive Optimization Control Technology of Rolling Energy and Oil Consumption in Double Cold Rolling

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    DOI:10.2355/isijinternational.ISIJINT-2018-723

    In double cold rolling process, rolling energy and oil consumption is normally controlled separately, thereby causing a high comprehensive cost. This study investigated a calculation model of plate-out oil film thickness on strip surface, oil film thickness in deformation zone, friction coefficient, bite angle, forward slip, rolling force, rolling power, rolling energy consumption, and rolling oil consumption. Subsequently, the effect of emulsion flow and concentration on rolling energy and oil consumption comprehensive cost was quantitatively analyzed. On this basis, an objective function of rolling energy and oil consumption comprehensive cost was proposed, and the corresponding comprehensive optimization control technology for rolling energy and oil consumption was developed. Through a field application of this technology, the reduction of rolling energy and oil comprehensive consumption cost was achieved by optimizing emulsion flow and concentration comprehensively. Thus, a significant economic benefit was created with further popularization and application values.
  • Chemical Structure of Si–O in Silica Fume from Ferrosilicon Production and Its Reactivity in Alkali Dissolution

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    DOI:10.2355/isijinternational.ISIJINT-2018-516

    As an environmentally hazardous waste, silica fume was considered as a potential alternative for cement and SiO2 production. The structure of Si–O was highly relevant to the reactivity of Si conversion for efficient utilization. In this study, the characteristic and chemical structure of Si–O in silica fume were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). Deconvolution of XPS and FTIR spectra into elementary profiles was carried out to analyze the structural components. As a result, the valence state, bonding structure and elementary unit in the Si–O network of silica fume were determined. Then, the reactivity silica fume with alkali solution was studied involving the effects of NaOH concentration and temperature. The staged kinetics behavior was associated with the structure of Si–O bonds, and the activation energies were determined. The results thus provided fundamental information for the utilization of silica fume for SiO2 production and geopolymer.

Article Access Ranking

26 May. (Last 30 Days)

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