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

ISIJ International Advance Publication

  • New Process for Resource Utilization of Converter Gas and Simulation on the Combustion of Converter Gas

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    DOI:10.2355/isijinternational.ISIJINT-2017-400

    A new process for resource utilization of converter gas is proposed to produce CO2 at a lower cost in this paper. Converter gas is burned in O2–CO2 atmosphere instead of O2–N2 atmosphere in a closed combustion furnace. Flue gas with high concentration of CO2 can be used as low-grade CO2 directly or be purified as raw gas for preparing high-purity CO2. Both the low-grade CO2 and high-purity CO2 can be recycled for the converter blowing and sealing. In order to analyze the combustion characteristics of converter gas, numerical simulations based on a three dimensional combustion furnace model were carried out. Volume fraction of N2 in combustion flue gas dropped from 63.37% to 3.92%, meanwhile CO2 concentration in flue gas reached 95.08% when the N2 in air was totally replaced by CO2. In addition, to control the CO content in flue gas within the safety criterion, lower stoichiometry is an optimal solution for the converter gas compete combustion.
  • A Model for the Reduction of Metal Oxides by Carbon Monoxide

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    DOI:10.2355/isijinternational.ISIJINT-2017-630

    The reduction of metal oxides by carbon monoxide is a very significant reaction in metallurgical and chemical industries. In current study, a kinetic model describing the reduction reaction of metal oxides by CO has been developed. The model is in the analytic function of parameters such as temperature, radius of the particle, CO content, density of metal oxides and time, which is, therefore, convenient for usage and theoretical analysis. The developed model can be applied to describe the reduction kinetics of metal oxides under both isothermal and non-isothermal conditions. Particularly, it can be used to describe the kinetics of both single reduction reaction (single reaction interface) and dual reduction reactions (double reaction interfaces, such as, the reduction of Fe2O3 to FeO with Fe3O4 being the intermediate product) as well. Application of the developed model to practical systems validated that its predicted values agreed very well with the experimental data in literatures.
  • Effects of Preheating Temperature and Time of Hongge Vanadium Titanomagnetite Pellet on Its Gas-Based Direct Reduction Behavior with Simulated Shaft Furnace Gases

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    DOI:10.2355/isijinternational.ISIJINT-2017-486

    As a part of ongoing efforts to develop a novel clean smelting process of Hongge vanadium titanomagnetite (HVTM), the effects of preheating temperature and time of HVTM pellet (HVTMP) on its gas-based direct reduction behavior with simulated shaft furnace gases were investigated in this paper. The results showed that the compressive strengths of preheated and roasted HVTMP could be improved by increasing the preheating temperature and time to some extent. The induration mechanism of HVTMP with different preheating conditions was further deeply explained. Increasing the preheating temperature and time of HVTMP accelerated its subsequent reduction rate, however, from 900 to 1000°C, the reduction rate decreased. The preheating temperature and time of HVTMP had little effect on the final phase composition of reduced HVTMP. A schematic illustration was proposed to describe the effects of preheating temperature and time of HVTMP on its subsequent reduction swelling. In the practical industrial production of HVTMP, the preheating characteristics should be optimized to meet the requirements of compressive strength and reduction swelling of HVTMP smelting in the gas-based shaft furnace. This study aims to provide both theoretical and technical basis for the effective utilization of HVTM either in blast furnace or shaft furnace.
  • Carbothermic Reduction of Vanadium-Titanium Magnetite in Molten NaOH

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    DOI:10.2355/isijinternational.ISIJINT-2017-515

    The carbothermic reduction experiments were carried out for vanadium-titanium magnetite in alkaline molten in argon atmosphere at high temperatures. The effects of reduction temperature, carbon content and addition agent on the formation of pig iron containing vanadium were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD patterns of reduced slags results showed that Fe phase disappeared and the main phase of the reduced sample were Na16Ti10O28, CaTiO3, and Na1.66AlSiO4.33 when the reduction temperature was more than 1473 K when cooled in the air. The SEM pictures show that most of V exists in the crystalline phase, such as Na16Ti10O28, NaAlSiO4 and CaTiO3, when quenched in air slowly; and the vanadium is dispersed in the slag phase when cooled by water quickly. Furthermore, the effects of additive NaOH on the reduction were also studied, results show that NaOH could enhance the separation of iron and slag, promote the transformation of vanadium and titanium and inhibit the vanadium enrichment in metal phase.
  • Influence of Cr2O3 Addition on the Gas-Based Direct Reduction Behavior of Hongge Vanadium Titanomagnetite Pellet with Simulated Shaft Furnace Gases

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    DOI:10.2355/isijinternational.ISIJINT-2017-544

    This paper investigated the influence of Cr2O3 addition on the gas-based direct reduction behavior of Hongge vanadium titanomagnetite pellet (HVTMP) with simulated shaft furnace gases. The reduction curves obtained indicated that the Cr2O3 addition revealed different effects on the reduction of HVTMP and the reduction process could be divided into three stages. X-ray diffraction showed that FeCr2O4 was formed by adding Cr2O3, which was hard to be reduced and had an adverse effect on the metallization degree of final reduced HVTMP. The morphology analysis revealed that the connected metallic iron particles were destroyed and their growth and connection were prevented during the reduction when Cr2O3 was added. With the increase of Cr2O3 addition, the growth of metallic iron whiskers was changed form close cluster to disperse location, and the number of metallic iron whiskers increased, which determined the extent of reduction swelling. In addition, the reduction swelling had relationship with the compressive strength of reduced HVTMP with different Cr2O3 additions. This study will not only establish a relationship between the Cr2O3 addition of HVTMP and its gas-based direct reduction behavior, but also contribute greatly to the effective utilization of HVTM in shaft furnace.
  • Changes in Microstructure and Chemical Composition of Deadman Coke of a 2800 m3 Industrial Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2017-644

    The paper examined the changes in microstructure and inorganic elements in their true mineral forms of the coke samples from various hearth locations using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) after the blow out and cool down of a 2800 m3 industrial blast furnace. The results illustrate that all deadman coke samples from fines to lumps were confirmed to be highly graphitized. Furthermore, the deadman coke was filled up with the accumulated KAlSiO4 during its descent process and the blast furnace slag which consisted of Ca2MgSi2O7–Ca2Al2SiO7 system and Ca2ZnSi2O7 phases. Besides the slag phases, the iron was also observed in the deadman coke soaked in the iron layer. Those cause that the mass of the deadman coke is about 1.62–2.82 times larger than that of the feed coke under the same conditions. Thus it may make the deadman which was designed to float sit on the hearth bottom as the permeation of the slag and the liquid iron into the deadman coke was not taken into consideration during the design process. We concluded that the slag phase below the taphole level is primarily derived from the blast furnace slag. Moreover, the deadman coke carrying final slag may come in contact with the hearth bottom and react with ceramic pad or carbon brick with a sitting deadman, thereby it results in degrading the hearth lining. Meanwhile, the slag phases below the taphole level can provide the material for the formation of skull to protect the hearth lining.
  • Physical and Mathematical Modeling of Multiphase Flows in a Converter

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    DOI:10.2355/isijinternational.ISIJINT-2017-680

    Fluid flow in converter bath, affecting the viability, effectiveness, and efficiency of steelmaking, plays a critical role in the productivity and quality level that can be achieved in the process. Due to a large quantity and diversity of the studies on the characteristics of the multiphase flow, it seems very necessary to make a systematic literature review on state-of-the-art developments in the steelmaking process. This paper presents the recent findings of the characteristics of the multiphase flow in the converter by means of physical and mathematical modeling and the resulting implications for simulating the process. Some representatives include supersonic oxygen jet, stirring and mixing, splashing and droplet generation, and energy transfer. The work summarized in this paper can give an in-depth understanding of the fluid flow in converter and provide references for future modeling of the converter steelmaking process. Future contributions to a fundamentally generalized modeling of the converter steelmaking are still needed. More profoundly, the modeling work can facilitate the real-time data-driven precise BOF process control and be an important component to the realization of intelligent manufacturing in steelmaking process.
  • Recognition of Slab Identification Numbers Using a Fully Convolutional Network

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    DOI:10.2355/isijinternational.ISIJINT-2017-695

    In the steel industry, slabs are manufactured with different amounts of alloying elements according to production purposes or final products. Because slabs have similar shapes, product identification is required to prevent inadequate production processes. In many steel mills, paint marking systems are widely used to inscribe slab identification numbers (SINs). As smart factory technology receives more attention in recent years, automatic recognition of SINs becomes more important for factory automation. The recognition of SINs is a challenging problem due to complex background of factory scenes and low quality of characters in SINs. To address this difficulties, this paper proposes a deep learning algorithm for recognizing SINs in factory scenes. Most existing recognition algorithms conduct text detection and classification using separate modules, and errors in each step are accumulated. The proposed algorithm employs a fully convolutional network (FCN) with deconvolution layers to integrate the recognition processes and improve the performance in processing time and accuracy. The main contribution of this work is on a novel type of ground-truth data (GTD) for the training of a FCN to recognize SINs in factory scenes. The relation between an input image and the corresponding GTD is directly trained in the manner of image-to-image training, and the FCN generates a prediction map that contains categorical information of individual pixels in an input image. Experiments were thoroughly conducted on industrial data collected from a steelworks to demonstrate the effectiveness of the proposed algorithm.
  • Thermal Strength Characteristics and Mechanism of Iron Ore and Carbon Pellets in the Non-isothermal Reduction Process

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    DOI:10.2355/isijinternational.ISIJINT-2017-202

    The thermal strength characteristics and mechanism of iron ore and carbon pellets (ICP) in the non-isothermal heating process, including the effect of reducing agent, carbon content and heating rate on the thermal strength, were studied by the on-line test device of thermal strength, combined with the TG/DTG-DTA data, the samples microstructure and porosity after reduction. When ICP was damaged by external force at high temperatures, it existed in two states: crush and plastic deformation. The thermal strength of ICP slightly increased at 200°C–800°C, significantly decreased after 800°C and reached the minimum value at 1000°C. The thermal strength of ICP was changed by the combination of combined water evaporation, the reducing agent volatilization and the reduction reaction. At 200°C–1000°C, the thermal strength was derived from the molecular attraction between the particles and viscous force from bonding agent. But when the temperature higher than 1000°C, the thermal strength was served by metal iron continuous crystal. To obtain high thermal strength, the iron oxides in ICP should be reduced fast by using the reducing agent with low volatility, improving the heating rate and choosing the suitable reducing agent ratio, made the iron crystal grown rapidly and dense.
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    3. Effect of Coarse-grain and Low-grade Iron Ores on Sinter Properties ISIJ International Vol.57(2017), No.5
  • Phase Equilibrium Investigation for CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 System Relevant to Ti-bearing Slag System

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    DOI:10.2355/isijinternational.ISIJINT-2017-555

    In order to resolve the lack of thermodynamic information for the comprehensive unilization of Ti-bearing blast furnace slag, the phase diagram relevant to the Ti-bearing slag composition was widely investigated. In the present work, the phase equilibrium relationships were investigated for the CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 phase diagram system. The equilibrium phases were experimentally determined at 1 300°C and 1 400°C using the high temperature equilibrium technique followed by X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscope (EDX) analysis. The liquid phase (L), melilite solid solution ((2CaO·MgO·2SiO2, 2CaO·Al2O3·SiO2)ss) phase, perovskite (CaO·TiO2) phase, Al–Ti diopside phase and pseudobrookite solid solution (MgO·TiO2, Al2O3·TiO2)ss phase were found. Based on the experimental results, the 1 300°C to 1 500°C liquidus lines and phase diagram were constructed for the specified region of the CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 system.
  • Thermodynamics of Sulfur in Carbon Saturated Liquid Ferro-alloys Containing Ni, Mo and V at 1873 K

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    DOI:10.2355/isijinternational.ISIJINT-2017-509

    The spent catalysts discarded from the petroleum refinery operations contain a substantial amount of valued metals such as Ni, Mo and V together with high sulfur content. Recently, the smelting reduction process of this resource using the carbothermic reaction is being developed and commercialized to recover these metals in the form of carbon saturated ferro-alloys containing Ni, Mo and V. Sulfur can be picked up into alloy melts from the sulfur bearing spent catalysts during the smelting process. Therefore, thermodynamics of sulfur in these alloy melts is very important for producing low sulfur ferro-alloys. In the present study, thermodynamic interactions between those alloying elements and sulfur in liquid iron was studied using the slag/metal equilibration technique at 1873 K. The equilibrium sulfur distribution was measured between a slag with a known sulfide capacity and carbon saturated liquid Fe–V–Ni–Mo alloys of various compositions. The carbon solubility in liquid alloy was significantly changed with alloy composition. The specific effects of V, Ni and Mo on sulfur was determined by considering the effect of carbon on sulfur using Wagner's formalism as the first- and second-order interaction parameters as well as the second-order cross-product terms.
  • Nitrogen Supersaturation Process in the AISI420 Martensitic Stainless Steels by Low Temperature Plasma Nitriding

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    DOI:10.2355/isijinternational.ISIJINT-2017-451

    A high-density RF-DC plasma nitriding system was employed on AISI420-J2 martensitic stainless steel at 653 K, 673 K, and 693 K for 14.4 ks. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), and electron backscattered diffraction (EBSD) were utilized to make analysis and characterization of the nitrided layers. These layers with the thickness of 85 μm from the surface was mainly nitrogen super-saturated with formation of nitrides at the vicinity of surface. The nitrogen content depth profile was nearly constant by 10 at% except for the gradual decrease from the maximum content by 30 at% at the surface and for the decay toward the nitriding front end. The lattice expansion by the strain of 1.6 % drove the phase transformation from the original martensite to austenite. High plastic straining following this elastic lattice expansion also caused the grain size refinement from the original size of 10 μm down to 0.15 μm.
  • De novo Formation of PCDD/F during Sintering: Effect of Temperature, Granule Size and Oxygen Content

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    DOI:10.2355/isijinternational.ISIJINT-2017-392

    Integrated iron and steel industry is the major industrial source of dioxins or, more precisely, of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Their main source is the sintering plant (preparing iron ore fines as feed for the blast furnace) and EAF for steelmaking. The influence of temperature (300–600°C), feed granule size (4 fractions, from 0.5–1 to 4–8 mm) and oxygen content (5 to 15 vol.%) on PCDD/F-formation has been investigated during de novo tests, involving a feed composed from the various sintering raw materials in their typical proportions. These experiments were conducted using a lab-scale vertical tube reactor and PCDD/F in off-gas and residue were collected together for analysis. Some CuCl2 catalyst was wetly added, to ensure that PCDD/F-formation activity was well measurable. The experimental results show that dioxins peak at 350°C, a granule size of 2 to 4 mm and the highest O2 concentration tested (15 vol.%). Within each homologue group, the isomer signature has been further scrutinized, with special emphasis on the seventeen 2,3,7,8-substituted PCDD/F, as well as on the seven PCDD-congeners and two TCDF usually associated with chlorophenol precursor routes, with the purpose to throw more light on the mechanism of PCDD/F-formation. For the first time ever, a complete congener-specific analysis is presented for sintering effluent and discussed. From this study and a number of former and ongoing studies, it is clear that iron oxide is responsible for the high PCDF/PCDD-ratio and the relatively low level of chlorination of PCDF and PCDD.
  • Effect of Added Olivine on Iron Ore Agglomerate During Induration

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    DOI:10.2355/isijinternational.ISIJINT-2017-327

    Olivine is used extensively in iron-pellet production as an additive in LKAB blast furnace pellets, in order to improve the high temperature properties of the finished product during reduction. As the contribution of olivine into the process depends on the available surface area, the present study was designed to find out the effect of olivine and its fineness on the oxidation-sintering and subsequent dissociation of olivine in iron ore agglomerates.Agglomerates were exposed to different experimental conditions to study the effect of olivine on the behavior of magnetite and hematite at high temperatures. Olivine particles were found to react significantly only above 1000°C. Porosity of the final product was found to depend largely on olivine fineness. The finer the olivine the lower the porosity of the final product. It is found also that irrespective of the starting iron oxide the ratio between hematite and spinel phase was the same after heating in air. Olivine fineness affects significantly the rate of hematite dissociation, the finer the olivine the higher the dissociation rate. Upon cooling the weight lost due to the dissociation was again regained.
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  • Non-isothermal Reduction Behavior and Mechanism of Hongge Vanadium Titanomagnetite Pellet with Simulated Shaft Furnace Gases

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    DOI:10.2355/isijinternational.ISIJINT-2017-516

    As an integral part of developing a novel clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite (HVTM), the non-isothermal reduction behavior and mechanism of HVTM pellet (HVTMP) were investigated using simulated shaft furnace gases of dry pulverized coal gasification (DPCG), water-coal slurry gasification (WCSG), Midrex, and HYL-III in the current study. The results showed that the reduction degree significantly increased with the decrease of heating rate. The reduction degree was found to increase in the order of DPCG<WCSG<Midrex<HYL-III. An approximately reversed linear relation could be concluded that the compressive strength of reduced HVTMP decreased as the reduction swelling index increased. The phase transformations of valuable elements under non-isothermal reduction conditions could be described as follows: Fe2O3→Fe3O4→FeO→Fe; Fe9TiO15→Fe2.75Ti0.25O4→Fe2TiO4; (Fe0.6Cr0.4)2O3, Fe0.7Cr1.3O3→FeCr2O4; (Cr0.15V0.85)2O3→Fe2VO4. However, under non-isothermal reduction conditions, SEM results indicated that the reduced metallic iron could not be connected together to form a uniform continuous area even at 1 100°C. These results could provide both theoretical and technical basis for the comprehensive utilization of HVTM.
  • Modification of the Primary and Peritectic Phases in Directionally Solidified Cu-20 wt.% Sn Alloy by Magnetic Field

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    DOI:10.2355/isijinternational.ISIJINT-2017-557

    Directional solidification experiments on Cu-20 wt.% Sn peritectic alloy were carried out in a direct current magnetic field device to investigate the modification of the primary and peritectic phases. A precipitation of the acicular martensitic structure of peritectic phase was observed below the solid-liquid interface. The magnetic field increased the length of precipitation zone and moved the solid-liquid interface to high temperature side. Solid-state transformation of the peritectic phase was observed below the eutectoid temperature. The magnetic field increased first and then decreased the transformation. A transition of the primary dendrites from arrayed to nonaligned growth under the magnetic field was characterized and analyzed. 3D numerical simulations of the thermoelectric magnetic flows and the thermoelectric magnetic forces were performed. The modification of the primary and peritectic phases under the magnetic field should be attributed to the fluid flows in the liquid and the forces on the solid.

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