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

ISIJ International Vol. 59 (2019), No. 2

  • Experiments on Removal of Hydrophilic Fine Particles in Bubbly Flow

    pp. 209-215

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    DOI:10.2355/isijinternational.ISIJINT-2018-582

    It is commonly believed that the solid oxides, like aluminum inclusions, were easily removed by bubbles because of their poor wettability with molten steel. However the liquid oxides like ladle slags were hard to remove because of their good wettability. The purpose of this study was to reveal the removal rate coefficient of the hydrophilic particles, which simulated liquid oxides in molten steel, in bubbly flows. The water model experiments were carried out. The air was injected into water-particles mixtures in a rectangular tank and the amount of particles included in the mixture overflowed from the tank was measured.The experiments confirmed that bubbles have abilities to bring hydrophilic particles upward even though the particles do not adhere to the bubble interfaces. The hydrophilic particles are entrained into the bubble wake at a certain probability and dragged upward while riding on the liquid flow in the wake. The removal rate coefficient per a bubble increases with the bubble diameter whereas the increase in the number of bubbles deteriorates the efficiency due to the reduction of the wake volume which is effective for particle transportation.
  • Effect of EAF Slag Temperature and Composition on its Electrical Conductivity

    pp. 216-220

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    DOI:10.2355/isijinternational.ISIJINT-2018-507

    Slag practice is one of the most important factors in molten steel production. Physical and chemical properties of slag determine the efficiency of the production process. Slag electrical conductivity is the second effective parameter in slag practice after viscosity. During current study, effect of temperature, FeO, CaO, SiO2 content and basicity ratio B2 on slag’s electrical conductivity was studied experimentally. It was found that, electrical conductivity increases with increasing temperature, %FeO, %CaO and basicity B2. On the other hand electrical conductivity was decreased with increasing SiO2 content. Specific conductance and electric conductivity index for slag main constituents were also estimated.
  • Molecular Dynamics Simulation of Carbon Effect on the Thermal Physical Properties of the Molten Iron

    pp. 221-226

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    DOI:10.2355/isijinternational.ISIJINT-2018-513

    In this paper, the effect of the carbon on the thermal physical parameters of the molten iron at 1500 K–2500 K is studied using a molecular dynamics method based on the hybrid inter-atomic potentials. Results show that density of molten iron decreases linearly in accordance with the carbon or temperature rise, and such correlation is derived using a least square method. The viscosity of molten iron is also indicated to decrease with the temperature increase. In addition, the self-diffusion coefficient of molten iron is reducing with the carbon content rise. While the overall phonon thermal conductivity decreases along with the carbon content increase, the process appears to be fluctuating significantly.
  • Effect of Silica on Reduction Behaviors of Hematite-carbon Composite Compact at 1223–1373 K

    pp. 227-234

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    DOI:10.2355/isijinternational.ISIJINT-2018-613

    The influence of compositional changes in the SiO2–Fe2O3 binary oxide system on the reduction behavior of carbon-bearing compact was investigated at 1223–1373 K. Density functional theory (DFT) calculations were employed to investigate the adsorption behaviors of O–Si–O on various FeO surfaces in order to explore the mechanism of the conversion of FeO to Fe–Si–O phase. Chemical analysis, SEM-EDX, and XRD were carried to characterize the conversion mechanisms. According to experimental results, silica causes the decrease of the metallization ratio by hindering the reduction of FeO to Fe and facilitating the reaction of FeO to Fe–Si–O phases. The size of metallic iron granules diminishes gradually and the boundary between the iron phase and the slag phase becomes less obvious with increasing silica content, which greatly increases the contact probability of SiO2/liquid phases and FeO. For the three adsorption sites, the adsorption energies of Si atoms onto FeO surfaces are all obviously larger than that of the reducing gases, making it extremely difficult for the reducing gases to remove O atoms from FeO surfaces, as the DFT results show. Moreover, it is easier to form the Fe–O–Si phase on the FeO (110) surface since the adsorption energy of O–Si–O onto this surface is greater than that onto the FeO (100) and FeO (111) surfaces. Additionally, the charge of the O (FeO) 2p orbital, the Si 3p orbital, as well as the 3s, 3p, and 3d orbitals of the Fe atom take charge of the formation of Si–O–Fe bond.
  • Phosphorus Gasification during the Carbothermic Reduction of Medium Phosphorus Magnetite Ore by Adding Na2CO3

    pp. 235-244

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    DOI:10.2355/isijinternational.ISIJINT-2018-456

    For medium phosphorus magnetite ore, effects of carbon mixing ratio, reduction temperature and basicity on phosphorous gasification and iron metallization during carbothermic reduction were investigated using XRD, SEM-EDS and FactSage software, as well as the existing status of Fe and P in the Bayan Obo raw ore and the appropriate addition of Na2CO3. The obtained results show that magnetite grains and phosphorous containing minerals (apatite and monazite) are finely disseminated and closely associated with gangue minerals of carbonate, silicate and aluminosilicate. Moreover, adding 5 mass% Na2CO3 is capable of breaking the abovementioned gangue mineral weaved structure and promoting the reduction of phosphorous ores. Furthermore, the optimum condition for phosphorus gasification is carried out at reduction temperature of 1050°C, with the carbon mixing ratio and basicity of 15 mass% and 0.5, respectively. The corresponding dephosphorization and iron metallization are 31.61% and 96.35%, respectively. Both of the increased carbon mixing ratio and reduction temperature lead that the reduced phosphorous gas tends to migrate in the metallic iron phase. Besides, thermodynamic analysis demonstrates that the presence of SiO2 not only promotes the dephosphorization but reacts with FeO resulting in the formation of fayalite, which prevents FeO from deeper reduction to metallic iron. Meanwhile, the combination of CaO, CaF2 and SiO2 produces cuspidine and decreases the quantity of liquid phase, consequently increasing the dephosphorization more or less.
  • Effect of Mineral Elements Migration on Softening–melting Properties of Ti–bearing High Basicity Sinter

    pp. 245-252

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    DOI:10.2355/isijinternational.ISIJINT-2018-498

    The mineral elements migration behaviours of Ti–bearing high basicity sinter during softening–melting process, as well as its effect on softening–melting properties, are studied using scanning electron microscope and X–ray diffractometer. We can conclude that both MgO and Al2O3 content increase while TiO2 content increases first and decreases later overall in the slag phase from the original state to melting end. At softening stage, some perovskite dissolves into the slag phase and part of TiO2 and MgO in wustite phase transfer into the slag phase. The low melting temperature of the slag phase is the main factor for the low softening temperatures of Ti–bearing sinter. At melting stage, TiO2 in the slag phase is tiny and changes little. The low liquidus temperature and viscosity of the slag phase result in the low melting start temperature of Ti–bearing sinter. The slag phase melts great earlier than metallic iron while the unfused sponge iron still bounds large amounts of perovskite crystals. And then, iron collapses and releases the restrained crystals at a higher temperature, resulting in the second rise of pressure drop.
  • Experimental Study on the Physical Properties of Iron Ore Granules Made from Australian Iron Ores

    pp. 253-262

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    DOI:10.2355/isijinternational.ISIJINT-2018-508

    A fundamental experimental study was conducted to measure the physical properties of iron ore granules made from three types of Australian iron ores. In this study, some key physical property parameters, including apparent density, Young’s modulus and the coefficients of static and rolling frictions, of the iron ore granules with varying moisture content were investigated. The effect of granule size on the considered property parameters was also studied for the iron ore granules at the optimal moisture content which was determined by permeability pot packing test. The measurement results showed that both apparent density and Young’s modulus of iron ore granules generally decreased with moisture content due to the growth of adhering layer around the nuclei particles. The static friction coefficient generally increased with moisture content but, at lower moisture contents, its variation differed between the granule types. The rolling friction coefficient generally experience a minimum value as moisture content increased within the considered range. The moisture content for the minima varied with granule type due to the different characteristics of the ore types. At the optimal moisture content for each granule type, the apparent density of different granule size fractions showed variable values because of the heterogeneous composition of the raw mixture in each size fraction. The Young’s modulus and static friction coefficient showed slight downward and upward trends with the increase of granule size, respectively. The rolling friction coefficient is nearly independent of granule size.
  • Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) Iron Ore Sinter Bonding Phase Formation: Effects of Basicity and Magnesium on Crystallisation during Cooling

    pp. 263-267

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    DOI:10.2355/isijinternational.ISIJINT-2018-573

    The effects of basicity and Mg addition on the crystallisation during cooling of complex Ca-rich ferrite iron ore sinter bonding phases SFCA and Fe-rich SFCA was investigated using in situ synchrotron X-ray diffraction. In synthetic iron ore sinter mixtures, cooling of a high temperature (T = 1623 K) assemblage comprising magnetite and melt showed that decreasing basicity from B = 4.0 to 3.0 and 2.5 resulted in the formation of a Fe-rich SFCA phase being suppressed, with SFCA being the only Ca-rich ferrite phase to form initially from the melt at B = 2.5. Increasing the Mg concentration in the sinter mixtures to 1 and 3 wt% MgO resulted in an overall suppression of the amount of Ca-rich ferrite phase formation. However, Mg addition caused the formation of Fe-rich SFCA to be favoured over SFCA, with SFCA not observed to form at all during cooling in the 3 wt% MgO mixture. The absence of SFCA in the high-Mg experiment was rationalised on the basis that the Fe-rich SFCA structure accommodates more Fe2+ than the SFCA structure, thereby stabilising Fe-rich SFCA relative to SFCA through replacement substitution of Fe2+ by Mg2+. Observation of Fe-rich SFCA in sinter may be an indicator of localised high basicity, and/or, high Mg concentration, within a sinter blend.
  • Change in Composition of Inclusions through the Reaction between Al-killed Steel and the Slag of CaO and MgO Saturation

    pp. 268-276

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    DOI:10.2355/isijinternational.ISIJINT-2018-584

    The inclusion of CaO–Al2O3 is occasionally observed during the secondary refining of Al-killed steel. In this study, MgO and CaO saturated slag was reacted with Al-killed steel in a MgO crucible, and the dissolution behaviors of Mg and Ca from the slag and the change in composition of inclusions were considered. Both the MgO and CaO in the slag were reduced from the presence of Al in the steel, and the concentration of dissolved Mg and Ca increased with the reaction time and Al concentration. When the Al concentration in the steel was 0.25 mass%, the concentration of dissolved Mg was 30 ppm or higher, whereas that of Ca was only 0.3 ppm. The initial Al2O3 inclusions transformed into a MgO·Al2O3 spinel, and finally changed into MgO inclusions rather than CaO–Al2O3 type inclusions. When the Al concentration was 0.75 mass%, the dissolved Ca concentration increased to 0.9 ppm, and the CaO–Al2O3 type inclusion with MgO was observed at 120 min. When the Al concentration further increased to 2.5 mass%, the concentrations of dissolved Mg and Ca increased to 110 and 3 ppm, respectively. The initial Al2O3 inclusions transformed into MgO inclusions within 5 min, and a CaO-Al2O3-type inclusion with MgO was observed after a 10 min reaction period. Finally, all inclusions transformed into a CaO-Al2O3-type inclusion with MgO at 120 min.
  • Problems in Solidification Model for Microsegregation Analysis of Fe–Cr–Ni–Mo–Cu Alloys

    pp. 277-282

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    DOI:10.2355/isijinternational.ISIJINT-2018-557

    Microsegregation of a Fe–Cr–Ni–Mo–Cu alloy was studied with the calculation model on the basis of two-dimensional concept considering diffusion of solutes during and after solidification. The calculated results were compared with the previous experimental results of the microsegregation profiles obtained by random sampling method. At first, a calculation model was created by applying two database sets of diffusion coefficients reported on Fe(γ)-X binary and Fe–Cr–Ni systems. The results using the database of the Fe–Cr–Ni systems fitted the experimental data better than those using the Fe(γ)-X systems in the region of lower solid fraction (fs). Meanwhile, in the higher fs region, the calculated lines passed below the arranged experimental data plots particularly for Cr and Mo. This inconsistency could be attributed to the following problems:(a) Diffusion coefficients might be lower at the post solidification temperature.(b) Partition coefficients might vary with solidification progress.(c) The ratio of the solid/liquid interfacial area to the solid volume might vary with solidification progress.Further, Fe contents analyzed in the previous experiments were rearranged as they simply decreased, while Cr, Ni, Mo and Cu were rearranged dependently with the Fe data at each fs point to keep the law of mass conservation. This rearrangement showed that the “slope segment” appearing in the region of fs below 0.1 in random sampling method was attributed to the probable measurement error.
  • Dynamic Distributions of Mold Flux and Air Gap in Slab Continuous Casting Mold

    pp. 283-292

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    DOI:10.2355/isijinternational.ISIJINT-2018-609

    The distributions of mold flux and air gap in shell/mold gap have significant influences on the shell heat transfer in slab continuous casting mold. To describe the dynamic distribution characteristics of the mold flux and air gap, a three-dimensional thermo-mechanical model coupling with a complex interfacial heat transfer model was developed, in consideration of the interactions between the thermo-mechanical behaviors of solidified shell and distributions of mold flux and air gap. Based on these, the contact and heat transfer behaviors between the shell and mold copper plates, as well as the influence of wide face mold taper on the distributions of mold flux and air gap during a peritectic steel continuous casting were studied. The results show that the temperatures of copper plate hot faces beneath the bolt columns are higher than those beneath the deeper channels, and the calculated temperatures of copper plates coincide well with the measured data by thermocouples. Due to the thermal contraction, the shell corners in mold shrink away from mold corners as the slab moving downward, which causes the thick mold flux film and air gap concentrate around the corners and off-corners. As a result, the hot spots form at the shell off-corners. With greater wide face tapers, the thicknesses of mold flux film and air gap at wide face corner decrease. When the wide face taper increases to 4 mm, the air gap on shell wide face corner disappears near the mold exit.
  • Generation Mechanism of Driving Out Force of the Shaft from the Shrink Fitted Ceramic Roll by Introducing Newly Designed Stopper

    pp. 293-299

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    DOI:10.2355/isijinternational.ISIJINT-2018-615

    Ceramic roller can be used in the heating furnace conveniently because of its high temperature resistance. The roller consists of ceramic sleeve and steel shaft connected only under a small shrink fitting ratio because of the brittleness. However, the coming out of the shaft sometimes happens from the ceramic sleeve under repeated loading. Therefore, it is important to find out the driving out force to prevent the coming out failure. Based on the previous studies, a two-dimensional shrink fitted structure is considered by replacing the shaft with the inner plate and by replacing the sleeve with the outer plate. Then, the driving out force is focused in this study by introducing a newly designed stopper on the outer plate. The finite element simulation shows that the coming out phenomenon can be prevented due to the stopper installed on the outer plate. Then the mechanism of driving out force generation is clarified. Finally, the process of coming out is explained in terms of the residual displacement.
  • Effect of Brazing Temperature on Microstructure and Mechanical Property of High Nitrogen Austenitic Stainless Steel Joints Brazed with Ni–Cr–P Filler

    pp. 300-304

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    DOI:10.2355/isijinternational.ISIJINT-2018-442

    In this study, Ni–Cr–P filler was used for vacuum brazing of high nitrogen austenitic stainless steels (HNS). The microstructure and shear strength of HNS joints were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and universal testing machine. The results exhibit that Cr2N compounds are formed at the HNS/filler interface when the brazing temperature is lower than 1000°C. The brazing seam is composed of Ni–Fe solid solution and (Ni, Cr)3P compounds, and the content of (Ni, Cr)3P compounds decrease with the increasing of brazing temperature. The formation of Cr2N and (Ni, Cr)3P compounds is adverse to the joint strength due to their brittleness. The optimal shear strength of joints is 163 MPa when the brazing temperature is 1050°C.
  • Microstructure and Failure Analysis of Resistance Projection Welding of Nuts to AHSS with Capacitor Discharge Welding

    pp. 305-311

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    DOI:10.2355/isijinternational.ISIJINT-2018-425

    Resistance projection welding (RPW) of T-shaped nuts to Usibor1500 hot-stamping steel sheets was conducted using Capacitor Discharge Welding (CDW). The microstructure evolutions, failure modes, and failure mechanisms of the RPW joints were investigated. The results show that the microstructure of the joints is divided into three regions: the fusion zone (FZ), the heat affected zone (HAZ), and the base material (BM). Predominant HAZ softening occurs on the HAZ of the sheet side due to the formation of ferrite and tempered martensitic. There are three modes of RPW joint failure: interfacial failure (IF), pullout failure (PF), and projection failure. Due to the uneven distributions of tensile stress on the faying surface, the fracture of the joints in the IF mode is a combination of ductile and brittle fracturing. The crack of the PF mode is generated in a ductile manner, but propagates around the joint in a brittle way. The fracture morphology of the projection failure mode is of large cleavage faces and river patterns. The solidification crack around the shrinkage void changes the crack propagation path and leads to a brittle rupture. As the welding voltage increases, the joints fail in mix modes: the pullout and interfacial failure mode or the pullout and projection failure mode.
  • Evolution of Inclusions and Associated Microstructure in Ti–Mg Oxide Metallurgy Steel

    pp. 312-318

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    DOI:10.2355/isijinternational.ISIJINT-2018-445

    Evolution of inclusions from laddle furnace (LF) to continuous casting in Ti–Mg oxide metallurgy treatment were studied. The resuluts suggested that the composition of inclusions changed from MnS-MnO·SiO2 to (Ti–Ca–Mg–Al–O)–MnS. Furthermore, EDS results indicated that the content of Mg decreased because of reduction reaction, float and gasification. The average size of inclusions was decreased from 0.73 µm to 0.47 µm and the number density decreased from 977/mm2 to 595/mm2 after continuous casting. The microstructures changed from polygonal ferrite (PF) and ferrite side plate (FSP) to acicular ferrite (AF), PF and bainite (B) gradually after inclusion treatment (Ti–Mg oxide metallurgy) in LF furnace and Ca treatment in RH furnace. Heterogeneous nucleation of AF was observed on the surface of Ti–Mg oxides.
  • Coating Film Profiles Generated by Fluctuating Location of the Wiping Pressure and Shear Stress

    pp. 319-325

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    DOI:10.2355/isijinternational.ISIJINT-2018-413

    Impinging planar jets are a widely used means of removing excess drag-out coating material from steel strip in order to control the final thickness of the applied coating. A wide range of possible coating defects are known to occur for this process, many of which are suspected to have their origin in the spatio-temporal characteristics of the air jets. It is therefore of interest to improve understanding of the link between the unsteady flow behaviour inherent to impinging jets and the evolution of the coating free surface produced by the gas-wiping process. In this paper, the coating response, characterised by the amplitude and frequency of the coating thickness fluctuation, throughout both the active region of the gas-wiping jets and the region immediately downstream, is investigated using a numerical model. The pressure and shear stress profiles acting on the coating surface along the strip are imposed as time-varying inputs such that for both the pressure and shear the vertical location of the entire profile undergoes sinusoidal oscillation parallel to the strip. A range of amplitude-frequency combinations for the vertical oscillation of the profiles are employed to assess the combined effect of these parameters on the coating response. Additionally, the strip speed is a varied parameter. Both the magnitude of the coating thickness fluctuation and the corresponding shape of the coating surface profile along the strip are found to be dependent on the strip speed and the oscillation amplitude and frequency of the vertical location of the pressure and shear stress profiles.
  • Numerical Simulation of Decarburization Kinetics for Fe-3%Si Steel during Annealing

    pp. 326-335

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    DOI:10.2355/isijinternational.ISIJINT-2018-547

    In order to reduce the magnetic aging produced in the use of oriented silicon steels, the carbon content in the steel matrix of products is less than 50 ppm. In this study, the decarburization reaction kinetics on Fe-3% Si steel surface and the diffusion mechanism of carbon in the steel were analyzed during decarburization annealing. Based on the balance between carbon diffusion flux in the steel matrix and the decarburization reactions on steel surface, the mathematical model for decarburization of Fe-3% Si steel with oxidation behavior was established. The boundary conditions of the model were given and the model was solved by numerical method. The decarburization experiments were carried at different annealing time, annealing temperature and PH2O/PH2. Results showed that the residual carbon content in the steel decreased and oxygen content increased continuously as the annealing time increased. With the increase of annealing temperature and PH2O/PH2, the residual carbon content in the steel first decreased and then increased. But the oxygen content increased continuously. Based on the experimental results, the decarburization model was modified from three aspects, which were phase transition in steel matrix, temperature change of steel in heating process and parameters change of decarburization kinetics. When the decarburization model was modified, the values of simulated results were in good agreement with the experimental results, which proved the validity of the model.
  • Corrosion Behaviour of TiC Particle-reinforced 304 Stainless Steel in Simulated Marine Environment at 650°C

    pp. 336-344

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    DOI:10.2355/isijinternational.ISIJINT-2018-534

    Corrosion behaviour of 304SS and TiC-reinforced 304SS in simulated marine environment at 650°C, compared with that of 304SS in air, has been investigated. The corrosion of 304SS in marine environment is more severe than that in air due to the effect of NaCl and water vapor. For TiC-304SS, a finer microstructure and higher dislocation density formed by TiC addition accelerates chromium diffusion. The formation of TiO2 by the oxidation of TiC possibly assists chromia nucleation and increases the adhesion of chromia scale. As a result, corrosion resistance is increased. However, the corrosion rate of 304SS-6TiC is faster than that of 304SS-2TiC and the possible reason to cause this is discussed.
  • Fabrication of Superoleophobic Surface on Stainless Steel by Hierarchical Surface Roughening and Organic Coating

    pp. 345-350

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    DOI:10.2355/isijinternational.ISIJINT-2018-569

    Stainless steels is practically important corrosion-resistant metallic materials, and additional surface functionalities including self-cleaning, anti-fouling, anti-ice and snow sticking and fluid drag reduction by the introduction of superhydrophobic and superoleophobic surfaces are of recent interest. Here, we report the micro-/nano-hierarchical roughening of type 304 stainless steel surface by chemical and electrochemical etching and anodizing. Chemical etching in HCl + FeCl3 aqueous solution containing a surfactant introduces surface roughness of several tens micrometers scale and the electrochemical etching in HCl + HNO3 aqueous solution produces a number of etch pits of ~1 µm in size. Then, a porous anodic layer of the pore size of ~20 nm is formed on the etched surface by anodizing in ethylene glycol electrolyte containing 0.1 mol dm−3 NH4F and 0.1 mol dm−3 H2O. After fluoroalkylsilane (FAS) coating of the hierarchically rough surface to reduce the surface energy, the surface becomes superhydrophobic and superoleophobic; the advanced contact angle for hexadecane (surface tension of 27.6 mN m−1) is ~160° and the contact angle hysteresis is less than 10°. Since the FAS-coated flat surface is oleophilic, so that such hierarchically rough surface is of significant importance to achieve the superoleophobicity even for low surface tension liquids.
  • Effect of Sn Addition on Evolution of Primary Recrystallization Texture in 3% Si Steel

    pp. 351-358

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    DOI:10.2355/isijinternational.ISIJINT-2018-223

    The evolution of the primary recrystallization texture was investigated for 3%Si steel without and with solute Sn. The texture component just after the completion of recrystallization was {111}<112> in both the Sn-less steel and the Sn-added steel. However, while the {111}<112> orientation remained the main texture component in the Sn-less steel after grain growth at 850°C, the {411}<148> orientation replaced the {111}<112> orientation as the main texture component in the Sn-added steel. In Sn less steel, the frequency of low angle boundaries decreased during grain growth indicating the movement of low angle boundaries which are major boundaries around {111}<112> grains. The addition of Sn selectively suppressed the decrease of the frequency of low angle during grain growth. The Monte-Carlo grain growth simulation in which the mobility of grain boundaries depended on the grain boundary misorientation angle (ω) was conducted. The simulation results suggested that reducing mobility of low angle boundaries (ω<15°) and high angle boundaries (ω>45°) enhanced the development of {411}<148> grains during grain growth with high angle boundaries (15<ω<45°), which are major boundaries around {411}<148> grains. The difference in mobility between the low angle boundaries (ω<15°) and high angle boundaries (15<ω<45°) is caused by anisotropic solute drag effect on the grain boundaries and would result in the preferential texture evolution observed in the Sn-added steel.
  • Slow Strain Rate Tensile Test Properties of Iron-Based Superalloy SUH660 in Hydrogen Gas

    pp. 359-366

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    DOI:10.2355/isijinternational.ISIJINT-2018-539

    To investigate dependence of strain rate of tensile test for iron-based superalloy SUH660 (A286), tensile tests were conducted for the specimens in 70 MPa hydrogen gas and air at 150°C. Nominal stress-nominal strain curve of each strain rate in 70 MPa hydrogen gas showed same behavior to maximum load via yield point in comparison with that in air, however, each elongation at breaking point in 70 MPa hydrogen was a little shorter than that in air. The values of tensile strength didn’t depend on the strain rate in 70 MPa hydrogen as well as those in air. In addition, the difference in tensile strength wasn’t observed between that in 70 MPa hydrogen gas and that in air for the strain rate. However, it’s proved that relative reduction of area in 70 MPa hydrogen to that in air was significantly affected by strain rate of tensile test. Those values were 80%, 51%, and 32% in the case of strain rate 5.0×10−5, 7.5×10−6, and 1.25×10−6 s−1, respectively. The morphology of fracture surface also changed from dimple to quasi-cleavage (QC), with a decrease in strain rate. Simulation of hydrogen gas diffusion from surface to inside during experiment showed that the hydrogen diffusion layer of specimen with QC fracture surface (RRA 51%, strain rate 7.5×10−6 s−1) was only 0.25 mm in depth. That implies that hydrogen content at crack tips is much higher than that of simulation due to hydrogen concentration by a couple of defects. That tendency seems to become stronger with a decrease in strain rate.
  • Effect of F Replacing O2− on Crystallization Behavior of CaO–SiO2–Al2O3 Continuous Casting Mold Flux

    pp. 367-374

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    DOI:10.2355/isijinternational.ISIJINT-2018-422

    In the molten slag system of CaO–SiO2–Al2O3, F will replace part of the bridging oxygen in the Al–O network as bridging fluorine. The electronegativity of fluoride ions is greater than that of oxygen ions. By maintaining the molar number of metal cations, and using an equimolar amount of CaF2 to replace CaO, i.e., F instead of O2−, the main focus of this research is whether one can inhibit the crystallization of the CaO–SiO2–Al2O3 slag system. In this paper, the techniques of single hot thermocouple technique, X-ray diffraction and Raman spectroscopy were used to analyze the crystalline properties, the crystalline phases and the molten slag structure. The results show that with the increase in the amount of equimolar CaF2 replacing CaO, the structure of Q0 decreases in prevalence, the structure of Q2, Al–F–Al and Al–O–Si with high polymerization increases in prevalence, the critical cooling rate decreases, the high temperature precipitation material of the sample changes from dicalcium silicate to gehlenite, and there will be CaF2 precipitation at low temperature.
  • Evaluation of the Effect of Humic Acids on the Reductive Elution of Fe from Fe2O3 in a Saline, Seawater-like Medium

    pp. 375-380

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    DOI:10.2355/isijinternational.ISIJINT-2018-219

    A fertilizer composed of steelmaking slag and compost, which would be expected to supply dissolved Fe to the sea, was evaluated for use in a seaweed-bed restoration technique. The Fe species in steelmaking slag is present in the form of insoluble Fe(III)-oxides, but could be eluted by seawater via reducing reactions. Humic acid (HA) would contribute to such a reductive Fe elution because it can act as an electron donor/acceptor. In this study, the effect of HAs with added ascorbic acid (ASC) on the reductive elution of Fe from Fe2O3 into a saline medium (pH 8, I = 0.7 as NaCl) was evaluated by a laboratory-based method. After a 3-day incubation, approximately 3 µM of Fe(II) was eluted in the presence of 5 mM of ASC. The effect of reductive Fe elution was clearly enhanced by the co-presence of low concentrations of HA, due to the electron shuttling function of HA. When 5 mM ASC was used in conjunction with 5 mg of L−1 HA, which was derived from hard-wood bark compost, about 5 µM of Fe(II) was eluted. The function was attributed to the structural features of HAs, polyaromatic compounds, N-content and highly substituted aromatic compounds, all of which could enhance the reductive Fe elution process. The present study also provided a simple method to evaluate the efficiency of HA on the reductive Fe elution.
  • A Mechanism Model for Accurately Estimating Carbon Emissions on a Micro Scale of Iron-making System

    pp. 381-390

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    DOI:10.2355/isijinternational.ISIJINT-2018-239

    The research from the Reclaim Program in Los Angels and Tsinghua University shows the estimation error reaches up to 27%–50% via using the emission coefficient approach offered by IPCC. In principle, this approach only concerns the categories and amount of fuels though ignoring the systemic parameters and many process details. Therefore it is only applicable to the carbon emission estimation on a macro scale of an industry or a zone with a tolerable accuracy while the amount of carbon emissions is large. For more accurate estimation, a mechanism model considering the systemic parameters and the carbon metabolic processes of the iron-making system is established on a micro scale. In order to simplify the mechanism model, the iron-making system is divided into processing sectors and subsequently the carbon metabolic behaviors on systemic boundaries of sectors are parameterized for constructing the multiple agents. All agents are assembled by using the Petri net that indicates the links of sectors and the corresponding operation sequences. The mechanism model based on Hybrid PN–MaS formulates the quantitative relation between the carbon emission and systemic parameters and therefore can be used to accurately estimate the carbon emission from the iron-making system with multiple blast furnaces. Subsequently the systemic parameters including the allocation of materials, fuels, and the processing control parameters are discussed considering the objective of carbon emission reduction for the iron-making system on a micro-scaled level.

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