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

ISIJ International Vol. 58 (2018), No. 3

  • Measurement for Contact Angle of Iron Ore Particles and Water

    pp. 379-400

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    DOI:10.2355/isijinternational.ISIJINT-2017-424

    Contact angle, as a key index for the wettability of iron ore particles by water, is of very important for the iron ore processing like beneficiation, sintering and pelletizing.Methods developed for measuring the contact angles generally can be divided into direct and indirect methods, which were summarized in present study and their advantages and disadvantages are all compared. Capillary rise method may be the most applicative approach for porous particles.Most of the contact angles between iron ore particles with water reported in the literatures were collected and the influence of the physical and chemical properties of iron ore particles were analyzed. The result shows that iron ore particles are hydrophilic and its water contact angles are influenced by the complicate interaction of chemical compositions, especially the content of oxy-hydroxides and the surface morphology. Generally, the water contact angle of goethite is the smallest. Complicate surface morphology suggest a better wettability. Furthermore, the penetration behavior of natural iron ore particles and synthetic iron ore particles are obviously different during the contact angle measurement. Compared with sessile drop method, capillary rise methods are more suitable for the measurement of natural iron oxides. Some empirical equations to predict the contact angle were collected and compared. The wettability can be improved by increasing the surface morphology of particles, coating of iron ore particles, and high-temperature treatment.
  • Nitrogen Supersaturation Process in the AISI420 Martensitic Stainless Steels by Low Temperature Plasma Nitriding

    pp. 401-407

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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.
  • Thermodynamics of Sulfur in Carbon Saturated Liquid Ferro-alloys Containing Ni, Mo and V at 1873 K

    pp. 408-414

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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.
  • Non-isothermal Reduction Behavior and Mechanism of Hongge Vanadium Titanomagnetite Pellet with Simulated Shaft Furnace Gases

    pp. 415-421

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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 1100°C. These results could provide both theoretical and technical basis for the comprehensive utilization of HVTM.
  • Discrete Particle Simulation of Solid Flow in a Large-Scale Reduction Shaft Furnace with Center Gas Supply Device

    pp. 422-430

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    DOI:10.2355/isijinternational.ISIJINT-2017-545

    In large-scale shaft furnaces, a new design of center gas supply device (CGSD) is proposed and its installation may affect solid flow in the furnaces. Due to its short history and lack of production experience, the solid flow in large-scale reduction shaft furnaces with CGSD is still unclear. In this work, three-dimensional solid flow is examined by discrete element method. The effect of CGSD on solid flow is studied including flow patterns, descending velocity, residence time distribution, interactive force and abrasive wear. The results show that the CGSD could affect the solid flow profile. Compared with the case without CGSD, in the case with CGSD installed, the descending velocity below the bustle zone is larger; the averaged residence time of solid phase is decreased; the dispersed plug volume fraction and dead volume fraction are decreased, but the well-mixed volume fraction increases; the averaged inter-particle force of solid is lower. On the other hand, the simulations show that the largest abrasion is observed on the surface of CGSD, and thus the CGSD lifetime should be taken into account in practice. The study provides a cost-effective tool to understand and optimize solid flow when the CGSD is installed in reduction shaft furnaces.
  • Phase Equilibrium Investigation for CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 System Relevant to Ti-bearing Slag System

    pp. 431-438

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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 1300°C and 1400°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 1300°C to 1500°C liquidus lines and phase diagram were constructed for the specified region of the CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 system.
  • Thermal Strength Characteristics and Mechanism of Iron Ore and Carbon Pellets in the Non-isothermal Reduction Process

    pp. 439-445

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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.
  • Effect of Added Olivine on Iron Ore Agglomerate During Induration

    pp. 446-452

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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.
  • Reduction and Sulfurization Behavior of Tin Phases in Tin-bearing Iron Concentrates with Sulfates in Sulfur-bearing Stone Coal

    pp. 453-459

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    DOI:10.2355/isijinternational.ISIJINT-2017-568

    The tin could be effectively removed from tin-bearing iron concentrates through roasted with sulfur-bearing stone coal reported in previous researches, and the Sn volatilization ratio was obviously influenced by the amount of sulfur-bearing stone coal used. The reactivity of sulfate (FeSO4) in sulfur-bearing stone coal on the reduction and sulfurization behavior of cassiterite (SnO2) in tin-bearing iron concentrates was studied in this paper. The thermodynamic analysis and experimental results showed that Fe–Sn spinel was formed with the increase of FeSO4 amount during the roasting process, and it resulted in the tin volatilization ratio being relatively low (a maximum of 61.87%). Furthmore, the EPMA analysis indicated that the Fe–Sn spinel was mostly concentrated in the upper layer of the roasted residues, and these tin could be further removed and recovered by a physical separation process.
  • Fate of Nitrogen and Sulfur during Reduction Process of Carbon-containing Pellet Prepared by Vapor Deposition of Gaseous-Tar and the Influences of the Hetero Elements on the Reduction Behavior and Crushing Strength

    pp. 460-468

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    DOI:10.2355/isijinternational.ISIJINT-2017-577

    Influences of the vapor deposition (VD) atmosphere on the nitrogen/sulfur contents in carbon-containing pellet and the crushing strength during preparation by VD method of coke oven gas (COG) tar against cold-bonded pellet (CP) are first investigated using a flow-type quartz made fixed-bed reactor and a tensile and compression crushing machine. Although N in NH3 that is fed with simulated-COG components is not transferred into the prepared VD sample, some part of the S in H2S moves the VD sample; the carbonaceous materials derived from COG tar fill the pores of the CP. However, these elements do not affect the crushing strengths of the prepared VD samples. The N and S forms in the VD sample are then investigated using XRD and XPS, and the results show that these elements mainly exist as organic-N and -S in the VD samples. The fates of N and S in the VD sample during the reduction process are examined using a flow-type fixed-bed reactor under inert (He) and reduction (55%H2/He) atmospheres. The N species in the samples mainly evolve as NH3 and N2 at 400–1000°C, and the cumulative amount of N2 that evolves is greater than that of NH3. The H2S evolution begins at 400°C, and the profile provides the main peak at approximately 800°C. The amount of evolved H2S in 55%H2/He is greater than that in He. Although the reduction of the VD sample starts at approximately 400°C and stops at 1000°C, N and S species in the sample do not affect the reduction rate. In addition, the N and S in the VD samples do not influence the crushing strengths during heat treatment.
  • Effect of Oxygen and Sulfur in Molten Steel on the Agglomeration Property of Alumina Inclusions in Molten Steel

    pp. 469-477

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    DOI:10.2355/isijinternational.ISIJINT-2017-480

    The agglomeration force that acts between alumina cylinders in molten steel has been measured at different concentrations of oxygen and sulfur. Both oxygen and sulfur in molten steel reduce the agglomeration force between the alumina cylinders in molten steel and act as interfacial active elements. However, oxygen reduces the agglomeration force more significantly than sulfur. The agglomeration force that was obtained empirically has been analyzed by combining the formulated surface tension concerning molten steel containing oxygen and sulfur with a model representing the alumina interparticle interaction due to a cavity bridge force. Thus, this analysis enables the effect of oxygen and sulfur in the molten steel on the agglomeration property of the alumina inclusions in the molten steel to be evaluated. The agglomeration property of the alumina inclusions reduces with the increase in the concentration of oxygen and sulfur in molten steel. The reduction due to oxygen is much greater than that due to sulfur. Moreover, when the concentration of sulfur in molten steel increases, the alumina inclusions remain in an adhesion state due to the strong agglomeration force based on the cavity bridge force. However, because the agglomeration force markedly decreases when the concentration of oxygen in the molten steel increases, the alumina inclusions that have agglomerated once are likely to separate again due to the molten steel flow.
  • Influence of Soft Reduction on the Fluid Flow, Porosity and Center Segregation in CC High Carbon- and Stainless Steel Blooms

    pp. 478-487

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    DOI:10.2355/isijinternational.ISIJINT-2017-534

    Mechanical soft reduction, MSR, is today an established technique for reducing center segregation and center porosity in the continuous casting of blooms. The bloom cross section is reduced by pinch rollers to compensate for the downward liquid flow in the mushy zone due to solidification shrinkage. In the literature, results are reported on how much MSR quantitatively affects the center segregation, but not on how it influences the liquid flow velocities.An analytical mathematical model has been developed to calculate the liquid flow velocity along the strand taking into account the effect of height reduction at each pinch roller and the solidification shrinkage. The model considers how much of the total area reduction contributes to an area reduction of the liquid in the center and thus how it affects the flow velocities. The model is easy to apply and brings deeper understanding of the effect of MSR. Calculated results from different scenarios show that the area reduction should increase closer to the crater end. MSR trials on a high carbon steel grade show that the center segregation decreases in proportion to the amount of reduction and clarify the importance of applying a pinch roller just before the crater end. Elongations of the strand above ~1% gave inner cracks in this case. MSR of only 2% height reduction on a stainless steel bloom, type AISI 316, gave a substantial closure of visual center porosity on inspected longitudinal samples.
  • Dissolution Behavior of Mg from MgO–C Refractory in Al-killed Molten Steel

    pp. 488-495

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    DOI:10.2355/isijinternational.ISIJINT-2017-593

    MgO–C refractory is a widely employed refractory in steel refining and it is considered as a Mg source to form MgO·Al2O3 spinel inclusions in steel melt. In this study, MgO–C refractories with various carbon contents were immersed into Al-killed molten steel to investigate the dissolution behavior of Mg from MgO–C refractory. The result showed that Mg gradually dissolved into the steel melt from the refractory, and spinel inclusions were formed. Al in the steel melt reduced MgO in the refractory and consequently, Mg was dissolved into the steel melt. The dissolved Mg increased with the Al content in the steel melt. Moreover, C in the MgO–C refractory also reduced MgO in the refractory and supplied Mg to the steel melt. However, when the C concentration in the refractory was lower than 10 mass%, Mg was not supplied. The reduction in MgO by Al and C occurred independently, and the Mg content in the steel was the sum of the Mg supplied by these reactions. In some regions at the refractory–steel melt interface, a spinel layer was observed; however, this layer was not formed uniformly.
  • Behaviors of Coherent Flow Field with Various Shrouding Nozzles Arrangement

    pp. 496-504

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    DOI:10.2355/isijinternational.ISIJINT-2016-691

    In this paper, the effect of shrouding nozzles arrangement on flow field and stirring ability of coherent jet had been analyzed under two kinds of ambient temperatures. Compared with axial velocity and total temperature distribution in combustion experiment, the Eddy Dissipation Concept (EDC) model and detail chemical kinetic mechanism were adopted to represent the combustion reactions of the O2–CH4 jet flame in numerical simulation. Based on the experimental results of the water experiments and the numerical simulations, the coherent jet with different shrouding nozzles arrangements was used to research the application effect in a 100 t electric arc furnace, and then an optimum arrangement was confirmed.
  • Modification of the Primary and Peritectic Phases in Directionally Solidified Cu-20 wt.% Sn Alloy by Magnetic Field

    pp. 505-514

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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.
  • Magneto Hydrodynamic Calculation of Electromagnetic Stirring with Concave Shaped Free Surface Using Based Plane Shadow Method

    pp. 515-520

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    DOI:10.2355/isijinternational.ISIJINT-2017-564

    The electromagnetic stirring (EMS) is a method to stir molten metal using in the steel making like the continuous casting. Physics concerning the EMS includes electromagnetic and fluid dynamics with free surface, which is magneto hydrodynamics. Theoretical analysis of magneto hydrodynamics is limited and/or very difficult, so that the numerical computation is required to analyze magneto hydrodynamic phenomena. It means that Maxwell’s equations and Navier-Stokes equations must be solved simultaneously, and a lot of calculation time is expected. In this study, “based plane shadow method”, which is similar to the previous “R shadow method” but different from it in ability to be applied to any shape of the free surface, is suggested. Validity of the “based plane shadow method” is demonstrated by solving a magneto hydrodynamic problem simulating the continuous casting. It is shown that a comparable accuracy with solution obtained to solve the governing equations directly and a large amount of reduction in computational time achieve.
  • Estimation of Lubrication and Heat Transfer by Measurement of Friction Force in Mold

    pp. 521-526

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    DOI:10.2355/isijinternational.ISIJINT-2017-562

    In the continuous casting process of steels, the mold flux infiltrated in between a mold and solidified shell plays an important role to optimize lubrication and heat transfer to establish not only stable operation but also good surface quality of slabs. Therefore, lubrication and heat transfer was evaluated by measuring friction force attributed to the mold oscillation along with a lubrication model. The friction force was measured with a slab caster equipped with hydraulic oscillators, to understand how the friction force was affected by continuous casting factors such as the mold oscillation conditions, mold flux properties and casting speed.It was found that the friction force was proportional to the velocity of the slab relative to the mold. The lubrication condition behaved as if it was fluid with the casting speed higher than 1.4 m/min.In addition, the temperature dependence of viscosity of the molten flux was accounted for to develop a new fluid lubrication model. The present model showed that the lubrication layer thickness was approximately 50 µm.Further, heat transfer through the mold flux was evaluated by the lubrication model revealing thermal resistance of the solidified flux layer, proving that the resistance caused by the crystallized flux was larger than that by glassy flux.
  • Characterization of Surface Oxidation and Numerical Simulation of Oxidation Kinetics for Fe-3%Si Steel during Decarburization

    pp. 527-534

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    DOI:10.2355/isijinternational.ISIJINT-2017-492

    During the decarburization annealing process, the oxidized layer formed on the Fe-3% Si steel surface may affect its subsequent nitriding and secondary recrystallization. The decarburization experiment is carried out in the N2 + H2 + H2O at an annealing temperature 835°C. The morphology evolution of the oxidized layer on the steel surface under different annealing times is studied, and the distribution trend of silicon and oxygen in the oxidized layer is analyzed. For the phenomenon of selective oxidation behavior of Fe-3% Si steel, its oxidation kinetic model is established by using mass conservation equations, which is modified by probabilistic statistical method according to the experimental results. The results show that the oxidized layer of Fe-3% Si steel is composed of silica and fayalite after decarburization annealing. The oxidized layer thickens with the increase of annealing time. This oxidation kinetics model is suitable for calculating the mass fraction distribution of silicon and oxygen in the oxidized layer, the thickness of oxidized layer, and the content of oxygen in the steel. The model is a very powerful tool in the simulation of Fe-3%Si steel during decarburization.
  • Effect of Titanium Addition on High Temperature Workability of High Manganese Austenitic Steel

    pp. 535-541

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    DOI:10.2355/isijinternational.ISIJINT-2017-385

    In the present study, the high temperature workability of high manganese austenitic steel has been examined to prevent the grain boundary embrittlement cracking problems in the continuous casting process. As-cast Fe-22Mn-0.4C steel exhibited poor hot ductility behaviors at 900°C tensile test. Phosphorus segregation and BN precipitation at grain boundaries were mainly responsible for this deterioration. In order to enhance the hot ductility, titanium was added to this steel, and high temperature workability was compared in view of reduction of area in tensile test at 900°C. BN precipitation at grain boundaries was effectively suppressed by the formation of interior Ti(C,N) precipitates. Furthermore, phosphorus atoms, a grain boundary embrittlement element, were observed to segregate at Ti(C,N) interfaces in Auger electron spectroscopy and atom probe tomography. These results show that titanium addition in Fe-22Mn-0.4C steel can effectively improve the high temperature workability by decreasing the segregation of phosphorus at grain boundary.
  • Randomization of Ferrite/austenite Orientation Relationship and Resultant Hardness Increment by Nitrogen Addition in Vanadium-microalloyed Low Carbon Steels Strengthened by Interphase Precipitation

    pp. 542-550

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    DOI:10.2355/isijinternational.ISIJINT-2017-537

    Interphase precipitation of nano-sized alloy carbides is recently used to strengthen low carbon steels for its excellent contributions to strength and formability. The effects of nitrogen addition on the hardness of vanadium-microalloyed low carbon steels were investigated by considering both the dispersion of interphase precipitation and the ferrite/austenite crystallography. Three-dimensional atom probe analysis reveals that interphase precipitation of vanadium carbide is hardly affected by increasing the nitrogen content, although the nanohardness of ferrite is slightly increased. Another important factor determining the overall hardness of ferrite is found to be the ferrite/austenite crystallography. At lower transformation temperature, nitrogen addition reduces the amount of Widmanstatten ferrite and bainite, which are formed in absence of interphase precipitation. Instead, relatively harder allotriomorphic and idiomorphic grain boundary ferrite without Kurdjumov-Sachs orientation relationship against austenite are formed extensively.
  • Effect of Molybdenum Content on the Combined Effect of Boron and Molybdenum on Hardenability of Low-Carbon Boron-Added Steels

    pp. 551-560

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    DOI:10.2355/isijinternational.ISIJINT-2017-579

    Addition of Mo to boron-alloyed steel improves the hardenability by suppressing the precipitation of Fe23(C, B)6; this is known as the combined Mo-B effect. However, the maximum Mo content for the combined effect to occur is still unclear because previous studies on this effect mainly investigated steels with a Mo content of less than 0.80%. Therefore, in this study, 0.15% C steels containing more than 0.80% Mo were investigated to determine the maximum content required for the occurrence of the combined Mo-B effect. The combined effect increased with increasing Mo content up to 0.75%, after which it decreased. The optimum B content decreased from 12 to 11 ppm with increasing Mo content from 1.0% to 1.5%. In 1.0%Mo-20 ppm B steel and 1.5%Mo-20 ppm B steel, Mo2FeB2 precipitated instead of Fe23(C, B)6. Thermodynamic calculations revealed that the temperature at which Mo2FeB2 precipitation started increased with increasing Mo content in 20 ppm B steel. Moreover, Mo2FeB2 could precipitate even at a reheating temperature of 950°C. Thus, it is suggested that the maximum Mo content for the combined Mo–B effect on hardenability is determined by the precipitation of Mo2FeB2 mainly during reheating.
  • Tensile Properties of an Electrolytically Hydrogen Charged Duplex Stainless Steel Affected by Strain Rate

    pp. 561-565

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    DOI:10.2355/isijinternational.ISIJINT-2017-631

    To provide a reliable relationship between hydrogen embrittlement (HE) and the behavior of hydrogen in duplex stainless steels (DSSs), we evaluated the tensile behavior of electrolytically charged DSS (JIS SUS329J4L) specimens at various strain rates. Immediately after hydrogen charging, tensile tests were performed at strain rates ranging from 1.38×10−7 to 1.38×10−3s−1. Fracture surface was evaluated by scanning electron microscope (SEM) and the concentration of hydrogen was measured by thermal desorption spectroscopy (TDS).It was confirmed that elongation to failure was decreased with increasing charging time for testing at 1.38×10−6s−1, while ultimate tensile strength was not affected markedly by hydrogen charging. The extent of HE took a maximum at a strain rate of 1.38×10−4s−1. Tensile test results and results of fracture surface evaluation by SEM were consistent to each other: the fraction of smooth area (area without dimples) with respect to the whole fracture area also took a maximum at the strain rate of 1.38×10−4s−1. These results were correlated to the balance between hydrogen diffusion and hydrogen desorption during the test. By TDS, the concentration of the diffusive hydrogen was confirmed to increase with increasing charging time. Hence, the extent of HE was strongly dependent on the concentration of the diffusive hydrogen.
  • De novo Formation of PCDD/F during Sintering: Effect of Temperature, Granule Size and Oxygen Content

    pp. 566-572

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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.

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  1. blast furnace
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  9. heat balance
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