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

ISIJ International Vol. 56 (2016), No. 4

  • Mineral Phase Formation and Zinc Removal during Sintering of Filter Cake Wastes

    pp. 505-512

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    DOI:10.2355/isijinternational.ISIJINT-2015-485

    A large amount of filter cake wastes are produced from the gas cleaning systems of blast furnace (BF) ironmaking and basic oxygen furnace (BOF) steelmaking processes. The filter cake wastes cannot be directly recycled through the ironmaking process due to the high zinc contents and are therefore, predominantly, stockpiled. The storage of filter cake wastes presents a long-term environmental issue but also an opportunity to extract or recover the iron content, motivating a search for processes or technologies to allow their cost-effective recycling. In this study, two filter cake wastes from BlueScope Ltd. were sintered at 1100–1300°C in argon and air to evaluate the effects of temperature, gas atmosphere and carbon content on the mineral phase formation and zinc removal of sintered filter cake specimens. The fine particles in filter cake can be well aggregated by bonding phases (calcium ferrites and silicates) during sintering due to the presence of flux materials, CaO and SiO2, in the filter cake. Carbon and metallic iron in the filter cake reduced ZnO to zinc vapour during sintering, which enhanced the zinc removal of the filter cake in a reducing gas atmosphere.
  • Phase Equilibria Studies in the CaO–SiO2–Al2O3–MgO System with CaO/SiO2 Ratio of 1.10

    pp. 513-519

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    DOI:10.2355/isijinternational.ISIJINT-2015-486

    Phase equilibria and liquidus temperatures in the CaO–SiO2–Al2O3–MgO system with CaO/SiO2 weight ratio of 1.10 have been experimentally determined by means of high temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Isotherms in the interval of 20 K between 1613 and 1733 K were determined in the primary phase fields of dicalcium silicate, wollastonite, merwinite, periclase, spinel and melilite that are relevant to ironmaking slags. Effects of Al2O3, MgO and CaO/SiO2 ratio on the liquidus temperatures have been discussed to assist optimum operation of iron blast furnace. Compositions of the solid solutions corresponding to the liquidus have been accurately measured that will be used for development of the thermodynamic database.
  • Sulfide Capacity of CaO-SiO2-FeO-Al2O3-MgOsatd. Slag

    pp. 520-526

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    DOI:10.2355/isijinternational.ISIJINT-2015-524

    The sulfide capacities of CaO-SiO2-FeO-Al2O3-MgOsatd. slag were measured at 1823 K over a wide range of compositions using the thermochemical equilibrating technique. The experimental results indicated that MgO had a marginal effect on desulfurization because of its low thermodynamic driving force for sulfur ion stabilization in slag, whereas Al2O3 decreases the sulfide capacity because of its acidic behavior in the present slag system. The effect of FeO on desulfurization can be changed by the slag basicity because the Fe2+ cation competes with the Ca and Mg cations, which is reflected in changes in the sulfide stability of FeS in the slag. The depletion of Ca2+ cations in an acidic slag electrically bound Ca2+ ions with near non-bridging oxygen to create electric neutrality because of its higher ionicity. Thus, the competitive affinity of Fe, Ca, and Mg with sulfur in the slag plays an important role in the effect of the basicity of the slag on the stability of sulfide in a moderate slag composition range. Nonetheless, S2− ions form CaS instead of FeS in a basic slag because there are excess free Ca2+ ions.
  • Importance of Melt Generation and Properties in Iron Ore Sintering

    pp. 527-536

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    DOI:10.2355/isijinternational.ISIJINT-2015-489

    In iron ore sintering material coalescence leading to densification occurs in the flame front. Unless a certain level of material coalescence is achieved, the obtained sinter product will not have the necessary size or load-bearing strength requirements. The efficiency of this process is dependent on melt volume and flowability of the molten system at flame front. Melt volume is greatly affected by the assimilation process which depends on ore properties – composition, porosity and size. The aim of this study is to provide information on the effect of solids ratio and melt properties on coalescence. In a sinter plant these parameters alter with changing blend composition. In this study, the behaviour of tablets containing four different iron sources: porous and dense ores, sinter and a chemical reagent, was studied in two fashions: theoretically the influence of assimilation on the properties of the melt and the three-phase system was examined; by experiments with an electric furnace, material coalescence was quantified using sinter density and pore property analysis. Results show that the porous ore tablet was more deformable and had a higher densification degree compared with the dense ore tablet. The highest density was found for the tablets containing sinter and chemical grade reagents. The results indicate that increased level of porous ore or sinter of return fines may enhance coalescence in sintering.
  • Analytic Approach for the Effect of Interfacial Tension on the Liquid Drop Flow in a Simple Packed Bed

    pp. 537-545

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    DOI:10.2355/isijinternational.ISIJINT-2015-495

    In a packed bed system, the interfacial tensions of liquid drops highly affect their flow behavior by changing the direction of the interfacial tensions in the liquid-solid-gas interface. The vertical directional interfacial forces of a liquid drop in a packed bed of small particles were calculated using a 3-D analytic calculation model. Regardless of the wettability of a solid surface, the interfacial tension induces the resisting force against the gravitational force. In short, the interfacial tension limits the flow of a liquid drop along the direction of the gravitational force. In case two liquid drops of different phases directly contact each other in a packed bed, one of the interfaces of each drop is shared, and the influence of the interfacial force decreased so that the liquid drops could move down through the void between particles compared with the case a single drop. If the shared interface of two liquid drops of which one is non-wettable and the other is wettable has lower contact angle than that of the liquid-gas interface of the liquid drop, then the drops experience the downward force along the direction of the gravity in the larger range of the position in the packed bed.
  • Viscous Flow and Crystallization Behaviors of P-bearing Steelmaking Slags with Varying Fluorine Content

    pp. 546-553

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    DOI:10.2355/isijinternational.ISIJINT-2015-538

    The role of fluorine in the CaO–SiO2–MgO–Al2O3–FetO steelmaking slags was investigated through analyzing the viscous flow and crystallization behaviors of the slags. It was found that the viscosity decreased with increasing CaF2 content, which resulted from the decrease of the degree of polymerization (DOP) of the structures, as proved by O1s X-ray photoelectron spectroscopy (XPS) and magic angular spinning nuclear magnetic resonance (MAS-NMR) analysis. The continuous cooling transformation (CCT) diagrams of the primary crystals were also constructed. The results showed that CaF2 addition promoted the transformation of the primary crystal from spinel (MgFe2O4) to flourapatite (Ca5(PO4)3F), which was beneficial to the further enrichment of phosphorus. According to 19F MAS-NMR results, F ions mainly coordinate with Ca2+ ions to form Ca–F bond. Furthermore, considering the greater stability of P–O–Ca than that of Si–O–Ca bonds, most of the F ions behave as F–Ca–O–P band, which thus enhanced the formation of Ca5(PO4)3F. Additionally, the non-isothermal crystallization kinetics was further analyzed and the activation energy for the primary crystal growth was derived.
  • Effect of Flow Rate Controllers and their Opening Levels on Liquid Steel Flow in Continuous Casting Mold

    pp. 554-563

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    DOI:10.2355/isijinternational.ISIJINT-2015-440

    The present study investigates the mold flow structure at constant throughput condition for different slide-gate and stopper rod openings by utilizing computational fluid dynamic (CFD) modeling. Detailed validation of the CFD models are conducted using available experimental data and the performances of three different turbulence models, standard k-ε, realizable k-ε and k-ω SST are compared. The constant throughput casting operations for different slide-gate and stopper rod controller openings are simulated to quantify the effect of flow controllers and their opening levels on mold flow. The results indicate that for a slide-gate controlled system, the meniscus velocities are significantly affected by the changes in the opening level. The steady state operations do not provide the same mold flow if the slide-gate opening is altered. However, for the stopper rod controlled system the stopper rod opening level changes do not affect the meniscus velocities and the flow structures within the mold.
  • Validation and Simulation of Cellular Automaton Model for Dendritic Growth during the Solidification of Fe–C Binary Alloy with Fluid Flow

    pp. 564-573

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    DOI:10.2355/isijinternational.ISIJINT-2015-573

    Based on our previous developed 2D CA-FVM model, where the transport phenomna and kinetics conditions of solute-driven dendritic growth occurred in the solidification process with fluid flow were totally taken into consideration, an extensive model validation and furhter model application are demonstrated here. Firstly, the flow pattern of the lid-driven cavity is well predicted and quantitatively coincides with the classic benchmark solutions, as Re is in the range of 100 to 3200. Secondly, the numerical simulations of the free dendritic growth of Fe-0.82 wt%C alloy in the static undercooled melt and the convectional undercooled melt agree well with the LGK predictions in a relatively low undercooling range and the Oseen-Ivantsov solutions, respectively. After the detailed model validation, numerical simulations of the equiaxed/columnar dendritic growth of Fe-0.82 wt%C alloy with fluid flow have been carried out and the results show that the dendrite morphologies and solute profiles are significantly affected by the fluid flow and the asymmetries of the dendrite morphologies and solute profiles become more and more serious with the increase of the flow Péclet number. For the equiaxed dendritic growth in the undercooled melt with fluid flow, the solute is washed away from the upstream to the downstream region, resulting in accelerating the dendritic growth of the upstream tip and perpendicular tip and inhibiting the dendritic growth of the downstream tip. For the columnar dendritic growth in the lid-driven cavity, the circulation flow facilitates the side branch of the dendrite trunk edge, which faces to the incoming flow, and promotes the asymmetrical dendrite morphology and solute profile.
  • In-situ Study of Crystallisation Behaviour of CaO–SiO2–Na2O–B2O3–TiO2–Al2O3–MgO–Li2O Fluorine-free Mould Fluxes with Different CaO/SiO2 Ratios

    pp. 574-583

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    DOI:10.2355/isijinternational.ISIJINT-2015-583

    The increasing environmental concern for the fluorine emission in steel continuous casting makes the development of fluorine-free mould fluxes imperative. The main challenge in the development of fluorine-free mould fluxes is controlling heat transfer rate which is closely related to the crystallisation behaviour of mould fluxes. In this study, the crystallisation behaviour of CaO–SiO2–Na2O–B2O3–TiO2–Al2O3–MgO–Li2O fluorine-free mould fluxes with CaO/SiO2 mass ratios from 0.9 to 1.2 was examined using single hot thermocouple technique (SHTT) and double hot thermocouple technique (DHTT). Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams developed using SHTT showed that the crystallisation temperature increased and the incubation time decreased with the increase of CaO/SiO2 ratio. DHTT was used to simulate the temperature gradient between copper mould and strand in steel continuous casting. Analysis of the crystallinity evolution in the simulated temperature field showed an increased crystallinity of fluxes with the increase of the CaO/SiO2 ratio at certain times. The crystal phases and crystal morphologies formed in different conditions were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray energy dispersive spectroscopy (EDS). Phases formed in the process of the flux crystallisation included CaSiO3, Ca2MgSi2O7 and Ca11Si4B2O22. It revealed that CaSiO3 was the major phase at low CaO/SiO2 ratio. The amount of Ca2MgSi2O7 and Ca11Si4B2O22 increased with increasing CaO/SiO2 ratio.
  • Transient Behavior of Inclusions during Reoxidation of Si-killed Stainless Steels in Continuous Casting Tundish

    pp. 584-593

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    DOI:10.2355/isijinternational.ISIJINT-2015-694

    In the current study, steel samples in continuous casting tundish were taken at every 5–10 minutes to investigate the reoxidation behavior and inclusions in Si-killed stainless steel in the tundish during a casting sequence with three heats. Contours were employed to clearly illustrate the distribution of number density, diameter and area fraction of inclusions in composition ternary diagrams. After reoxidation of Si-killed stainless steel, [Al] and [Ca] in the steel were oxidized and decreased to extremely low levels in the reoxidized region of the molten steel. A large number of MnO-riched small inclusions as transitional products were generated by the oxidation of high [Mn], and gradually decreased. The population density function (PDF) of inclusions tended to a power law type function (f(r)=4.54×10−5·r−3.66). Moreover, thermodynamic calculation illustrated that, the increase rate of MnO and SiO2 content in liquid inclusions are much faster than that of Al2O3 and CaO during reoxidation of Si-killed stainless steel, while solid inclusions become predominant and transfer from CaAl4O7 to CaAl12O19 to Al2O3 in Al-killed stainless steel.
  • Viscosity Property and Structure Analysis of FeO–SiO2–V2O3–TiO2–Cr2O3 Slags

    pp. 594-601

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    DOI:10.2355/isijinternational.ISIJINT-2015-457

    In order to clarify the viscosity of FeO–SiO2–V2O3–TiO2–Cr2O3 system as the main components of vanadium slag with varied Cr2O3 and TiO2 contents, the viscosity and structure characteristics of the slag were investigated by the rotating cylinder method and Raman spectroscopy, respectively. The results showed that the viscosity was decreased to 3.5 Pa·s at temperature above 1534 K for the FeO–SiO2–V2O3 system, and the polymerization degree of this system was low due to the main structure of silicate as monomer. Meanwhile, V3+ mainly existed in the form of V–O–V as a chain structure in FeO–SiO2–V2O3 system, which slightly enhanced the polymerization degree of the slag. With the introduction of 6 mass% Cr2O3 into FeO–SiO2–V2O3 system, the viscosity increased rapidly and was decreased to 3.5 Pa·s until temperature higher than 1767 K, and the polymerization degree of the slag was enhanced drastically due to the formation of Q2 and Cr–O–Cr band in a chain structure as well as the formation of Q3 species in a sheet structure. Furthermore, part of the chromium existed in the form of the high melting point of spinel (FeCr2O4). With the introduction of 13 mass% TiO2 into the FeO–SiO2–V2O3–Cr2O3 system, the viscosity decreased and was of 3.5 Pa·s at 1624 K, and the polymerization degree of the slag became weak due to the formation of discrete Si–O–Ti and Ti–O–Ti inhibiting the formation of sheet structure and hampering the crystallization of FeCr2O4 in molten slag, which was advantageous to decrease the viscosity of FeO–SiO2–V2O3–Cr2O3–TiO2 system.
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  • Microstructural Characteristics with Various Finish Rolling Temperature and Low Temperature Toughness in Hot Rolled Nb–Ti Ferritic Steel

    pp. 602-609

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    DOI:10.2355/isijinternational.ISIJINT-2015-297

    In order to investigate the effects of finish rolling temperature on the microstructural characteristics and fracture mechanism of Nb–Ti ferritic steel, the samples with various finish rolling temperature have been observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results indicated that both ferrite grain size and volume fraction of (Nb,Ti)C precipitates decreased with the decreasing finish rolling temperature, but the size of (Nb,Ti)C precipitates changed little with the finish rolling temperature. All of these factors caused the yield strength, tensile strength and elongation remained similar. However, the low temperature toughness was significantly influenced by the finish rolling temperature. Based on the observation results of fracture surface of samples tested at −40°C, the fracture type of steels with finish rolling temperature of 940°C and 910°C was brittle, while the fracture of steel with finish rolling temperature of 880°C was ductile. At last, the crack initiation and propagation mechanism is elucidated in details. At −40°C, both intergranular cracks and transgranular cracks existed in the steels finish rolled at 940°C and 910°C, and only microvoides were observed in the steel finish rolled at 880°C with high toughness.
  • Formability of Al-killed AISI 1040 Medium Carbon Steel for Cylindrical Cup Formation

    pp. 610-618

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    DOI:10.2355/isijinternational.ISIJINT-2015-571

    The basic formability of Aluminum-killed AISI 1040 graded medium carbon steel (cold rolled followed by hardening and spheroidization tempering) has been characterized by uniaxial tension, compression, bending, and Erichsen cup tests.The results shows a good strength (~634 MPa) - ductility combination, high strain hardening exponent, normal plastic anisotropy value >1 and a considerably low planar anisotropy. The compressibility, bendability and biaxial strechability characteristics of the steel also signify its formability behavior in different loading states. The strain analysis on tensile and Erichsen cup specimens has provided deeper information on its strain dispersibility as well as necking tendency in both uniaxial and biaxial states.The actual press formability also has been investigated by applying a process consisting of multistage deep drawing accompanied with wall ironing, without using blank holder and with intermediate stress relieving treatment. Thus ~56 mm long cylindrical cups, ~36.85 mm diameter and ~3.8 mm wall thickness, have been manufactured from 12 mm thick and 60 mm diameter circular blanks in a preformed shape. This experiment has yielded significant values of few press formability parameters in terms of draw ratio, draw reduction, ironing ratio, ironing reduction and etc. Further, by drawing comparisons with few sheet metals, the competitiveness of the steel has been shown with an objective to enlighten on its line of applications as per customer demands.
  • Effect of Titanium on Hot Deformation Behaviors of Boron Microalloyed Steel

    pp. 619-627

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    DOI:10.2355/isijinternational.ISIJINT-2015-605

    The hot deformation behaviors of titanium-free and titanium-treated boron microalloyed steel were investigated at the temperatures from 850°C to 1100°C and strain rates from 0.1 s−1 to 10 s−1 on Gleeble-2000 thermo-mechanical simulator. It was found that the flow stress of the titanium-treated steel is lower than that of titanium-free at lower strain rates, indicating that titanium addition generates a softening effect. The flow stress constitutive equations of hot deformation were developed for the experimental steels, the activation energy of titanium-treated steel (299.7 kJ·mol−1) is higher than that of the titanium-free steel (286.9 kJ·mol−1). Additionally, it is interesting to note that the peak and critical strain are lowered by titanium addition, indicating that titanium has the ability to promote the onset of dynamic recrystallization. However, the dynamic recrystallization kinetics of titanium-free steel is faster than that of titanium-treated steel.
  • Effects of Surface Conditions on Spray Cooling Characteristics

    pp. 628-636

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    DOI:10.2355/isijinternational.ISIJINT-2015-609

    The influence of surface conditions such as scale thickness and surface roughness on water spray cooling and air jet cooling characteristics was investigated experimentally. SUS304 stainless steel with the thickness of 20 mm was used as the cooled sample. An artificial scale layer was formed on the sample surface by thermal-spraying using Al2O3 powder. The thickness of the Al2O3 layer was varied from 50 µm to 210 µm. A sample without an artificial scale layer was also studied; in this case, the surface was roughened by shot blasting up to 20 µmRa.
    As a result, the artificial scale layer showed a thermal resistance function in both water spray cooling and air jet cooling. In water spray cooling, the characteristics of which depend on surface temperature, the cooling rate during film boiling and the apparent quenching temperature at the interface increased with Al2O3 scale thickness. Surface roughness enhanced the cooling rate during film boiling and resulted in a higher quenching temperature in spray cooling. In air jet cooling, heat flux increases with surface roughness, but this tendency can be seen only with larger flow rates. Surface roughness has a much stronger influence on heat flux in water spray cooling, even though the average heat flux is not as large. In this research, the heat flux during impingement of water droplets was estimated to be much higher than that in air jet cooling. This is thought to explain the difference in the influence of surface roughness on cooling characteristics with the two cooling methods.
  • Numerical Simulation and Parameters Optimization of Laser Brazing of Galvanized Steel

    pp. 637-646

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    DOI:10.2355/isijinternational.ISIJINT-2015-467

    In order to study the heat phenomenon of laser brazing galvanized steel, the experiments of laser brazing were carried out, in which the base metal is galvanized steel sheets and CuSi3 is used as filler metal. The numerical simulation of temperature field was carried on by the finite element method, and the simulation result was validated through comparative experiment. The composite heat source model of gauss double ellipsoid was used. Temperature field of different process parameters have been calculated. The results show that: The peak temperature and temperature gradient on the joint are lower when the laser power is 1600 W, the brazing speed is 0.96 m/min. Response surface methodology was applied to the simulation data, and mathematical models was built based on Box-Behnken Design using linear and quadratic polynomial equations. The results indicate that the proposed models predict the responses adequately within the limits of brazing parameters being used. The optimum brazing parameters were found, and it is more favorable to form the brazed joint of good quality at the laser power of 1600 W, brazing speed of 0.96 m/min, filler wire speed of 1.19 m/min, defocusing distance of 30 mm.
  • Experimental and Numerical Investigation of Trailing Heat Sink Effect on Weld Residual Stress and Distortion of Austenitic Stainless Steel

    pp. 647-653

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    DOI:10.2355/isijinternational.ISIJINT-2015-659

    In this study, welding with a trailing heat sink was applied to austenitic stainless steel for reducing the weld residual stress and distortion. The effects on temperature profiles, residual stress and distortion were experimentally investigated through the use of gas tungsten arc welding with and without a water-cooling device. As the results, the weld residual stress and distortion can be reduced without affecting the weld penetration by welding with a trailing heat sink. Numerical investigation was also performed using the three-dimensional thermal elastic-plastic finite element analysis. A numerical model of gas tungsten arc welding was constructed based on the physics of the welding arc. The calculated weld penetration, temperature profiles, residual stress and distortion were in good agreement with those measured under the same welding conditions. Using the simplified model of homogeneously distributed heat sink on the basis of the developed welding simulation, the effect of intensity of the heat sink on the weld residual stress and distortion was quantified. Furthermore, the mechanism of the reduction of weld residual stress and distortion was discussed based on the temperature distribution variation in welding with a trailing heat sink. Based on the results, the effectiveness of welding with a trailing heat sink in reducing the weld residual stress and distortion of austenitic stainless steel has been clarified.
  • Crevice Corrosion Resistance and Structure of Passive Film on Fe–Mn–Si–Cr–Ni Steel

    pp. 654-660

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    DOI:10.2355/isijinternational.ISIJINT-2015-634

    The crevice corrosion resistance of an Fe–Mn–Si–Cr–Ni (15 Mn) steel as a shape memory alloy was estimated by laser microscopy and statistical calculation of the corrosion depth, and the structure of the passive film formed on the steel was examined by EELS (Electron Energy Loss Spectroscopy) analysis using TEM (transmission electron microscopy). The crevice corrosion results were analyzed using a Gumbel distribution, and the mode (λ) and distribution parameter (α) of the maximum corrosion depth of the 15 Mn steel were found to be much smaller than those of 430 stainless steel (SUS: 16Cr – Fe). This shows that 15 Mn steel has a higher crevice corrosion resistance than 430 SUS steel. In AES and XPS analysis, the passive film of 15 Mn steel was shown to contain Fe, Mn, Cr, Si and Ni. From TEM-EELS, the passive film was found to consist of 2 layers. In the passive film, Cr and Si are thought to be effective early, with Ni preventing penetration of crevice corrosion. It was found that 15 Mn steel could maintain a passive film which was composed of effective elements in a crevice corrosion environment.
  • Effect of Ag Content on the Microstructure and Magnetic Properties of Grain-oriented Silicon Steels

    pp. 661-668

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    DOI:10.2355/isijinternational.ISIJINT-2015-498

    The effect of Ag content in the range of 0–0.026 wt%, on the precipitates, microstructure, texture and magnetic properties of five grain-oriented electrical steels have been studied. A small quantity of Ag atoms with content less than 0.005 wt% only existed in the form of solid solution and promoted the nucleation rate of grain with {111} orientation on the grain boundary during decarburizing process. However, when Ag level rised to 0.012 wt%, some supersaturated Ag atoms precipitated from the matrix and in the form of single Ag-rich particles which inhibited the nucleation of the grains with (111) orientation and promoted the nucleation of grains with other orientation, such as Goss-orientation, during decarburizing process. The average grain size of decarburized bands decreased continuously as Ag content rised from 0 to 0.026 wt%. Compared to those final recrystallized bands with other Ag contents, the final recrystallized bands containing 0.012 wt% Ag obtained slightly larger average grain size. As Ag content rised from 0 to 0.026 wt%, magnetic flux density (B8) firstly dramatically decreased and then abruptly increased, nevertheless, core loss (P1.7/50) firstly slightly increased and then obviously decreased in final recrystallized bands. Final recrystallized bands with 0.026 wt% Ag obtained the best magnetic properties, whose core loss and magnetic flux density were 1.140 W/kg and 1.467 T, respectively.
  • Development of Biaxial Tensile Test System for In-situ Scanning Electron Microscope and Electron Backscatter Diffraction Analysis

    pp. 669-677

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    DOI:10.2355/isijinternational.ISIJINT-2015-534

    For the further improvement of the press formability of steel sheets, it is important to clarify the relationship between macro mechanical properties and microstructure under multi-axial deformation state. The objective of this work is to develop the experimental system of in-situ observation and analysis for biaxial tensile deformation using electron back scatter diffraction patterns (EBSD) with scanning electron microscope (SEM). The appropriate shape of cruciform specimen for the system was examined first by using finite element analysis, and the biaxial tensile test system in vacuum SEM chamber was developed. In-situ observation of microstructure during equibiaxial tensile deformation was then conducted using the developed system and the proposed cruciform specimen. The material used in this study was an interstitial-free steel. It was validated by the comparison with the results obtained by the Marciniak type macro test that the developed system realized equibiaxial tensile deformation. Finally, some information obtained from SEM and EBSD analysis was illustrated. It was found for example that the grains with {001} plane orientations deformed easily and might cause the surface roughness.
  • Prediction of Ar3 during Very Slow Cooling in Low Alloy Steels

    pp. 678-684

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    DOI:10.2355/isijinternational.ISIJINT-2015-602

    Considering the partition behavior of substitutional alloying elements, a computing method is developed to predict the starting temperature of proeutectoid ferrite transformation (Ar3) in low alloy steels during cooling. The paraequilibrium γ/(α+γ) phase boundary temperature (denoted Para Ae3) and local equilibrium partition to no-partition transition temperature are calculated using Thermo-Calc software in Fe-C-M1, Fe-C-M1-M2 and Fe-C-M1-M2-M3 (M1, M2 and M3 denote substitutional alloying elements) low alloy steels. Compared with Ar3 taken from published CCT diagrams, it is found that the transition temperature from partitioned to no-partitioned growth agrees relatively well with Ar3 when the cooling rate is less than 1°C/min.
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  • Comparison of Hydrogen Embrittlement Resistance of High Strength Steel Sheets Evaluated by Several Methods

    pp. 685-692

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    DOI:10.2355/isijinternational.ISIJINT-2015-566

    Applications of ultra-high strength steel sheets to automotive bodies have expanded steadily in recent years. Various methods are used to evaluate resistance to hydrogen embrittlement (HE), which is one problem of ultra-high strength steels. In this study, the critical HE conditions obtained by the SSRT, CSRT and 4-point bending test were compared by using the same materials. The materials were two ultra-high strength steel sheets with tempered martensite microstructures, one with the SCM435 composition and the other a V-added steel containing many hydrogen trapping precipitations. The specimens were charged with hydrogen by the cathodic charging method. The specimens used in the SSRT and CSRT were machined with notches on both sides of the parallel part. The values of the stress concentration factor (Kt) of the specimens were 4.26 and 1.76. A coupon-shaped specimen was used in the 4-point bending test. The critical HE conditions evaluated by the average applied stress and the average hydrogen content of the specimen were different depending on the test methods. The HE conditions were also evaluated by the local stress and the local accumulated diffusible hydrogen content at the fracture initiation point. The critical condition evaluated by the 4-point bending test was located in a higher stress and higher hydrogen content region compared with the critical conditions obtained by the CSRT and the SSRT.
  • Development of Recrystallization Texture in Severely Cold-rolled Pure Iron

    pp. 693-699

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    DOI:10.2355/isijinternational.ISIJINT-2015-567

    The mechanism of recrystallization texture development is changed by the chemical composition of materials, cold-rolling reduction, and annealing conditions. This study discusses the development of recrystallization texture for severely cold-rolled pure iron. In cold-rolled iron with 99.8% reduction, the deformation texture was a strong α-fiber (RD//<011>) with high strain. During annealing in a temperature range from 20°C to 800°C, in this highly strained α-fiber, the microstructure started to recover from a low temperature. Thereafter, recrystallized grains began to appear at 350°C, and many recrystallized grains were generated at random locations. Their textural components were {100}, {211}, {111}, and {411}, which were already included in the α-fiber. At 550°C, recrystallization was completed, and the resulting recrystallization texture was similar to the original cold-rolling texture. This texture was developed by unique microstructural changes, which could be classified as continuous recrystallization. During grain growth stage, the recrystallization texture changed into the {100}<012> component presumably by the selective growth of recrystallized grains governed by the size effect.
  • Hydrostatic Pressure Dependent Crystal Plasticity by Homogenization-based Finite Element Method

    pp. 700-707

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    DOI:10.2355/isijinternational.ISIJINT-2015-644

    A crystal plasticity model considering the hydrostatic pressure dependence is presented and validated using several numerical examples. Some metallic materials clearly show higher flow stress under uniaxial compression than that under uniaxial tension, and this phenomenon is called the strength-differential (S-D) effect. Since the S-D effect often occurs in iron-based materials, the understanding and modeling of its mechanical characteristics is important in industrial and engineering fields. The S-D effect may result from the hydrostatic pressure dependence of plastic deformation. Therefore, in this study, a crystal plasticity model is modified to account for this dependence. The proposed model is combined with the homogenization-based finite element method. This model adequately reproduces the S-D effect observed experimentally, thus its advantages over the previously introduced Taylor polycrystalline model, which overestimates the flow stress and fails to represent the strong inhomogeneity of hydrostatic pressure distribution at a crystalline scale, is highlighted. In addition, initial and subsequent plastic work contours are evaluated and a forming limit diagram is analyzed to characterize the new model.
  • Enhancement of Marine Phytoplankton Growth by Steel-making Slag as a Promising Component for the Development of Algal Biofuels

    pp. 708-713

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    DOI:10.2355/isijinternational.ISIJINT-2015-341

    Growing phytoplankton for the production of biofuels is one of the expected alternatives to the usage of safer and renewable type of energy. Steel-making slag, a by-product of the steel manufacturing process, is known to contain nutrients such as iron, phosphate and silicate, which are essential for the growth of marine phytoplankton. A batch experiment was carried out to examine the dissolution of phosphate and silicate from steel-making slag and their effects on the growth of a common neritic marine diatom Skeletonema costatum. The dephosphorized slag used in this study released iron moderately, maintaining a constant concentration of dissolved iron, which highly differed from the results of iron sulfate (FeSO4) and iron powder used as references. FeSO4 showed a rapid increase in iron ion for several days but the concentration rapidly decreased due to hydrolysis. The growth of S. costatum was significantly enhanced by the addition of slag because the released ratio of silicate, phosphate and iron was close to the required ratio for the growth of phytoplankton. Therefore, steel-making slag is a promising component for the enhancement of phytoplankton growth in the production of algal biofuels.
  • Ultrasound-intensified Leaching of Gold from a Refractory Ore

    pp. 714-718

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    DOI:10.2355/isijinternational.ISIJINT-2015-476

    The effect of ultrasonic energy on the pretreatment and leaching of gold from the refractory ore was investigated. Firstly, the refractory ore was pretreated with sodium hydroxide under ultrasound. Secondly, the pretreated ore was leached under ultrasound. The leaching ratio of gold decreased with increasing of the ultrasound pretreatment time from 1 to 5 h and the NaOH concentration from 5 to 20 wt%. The ultrasound increased remarkably the leaching ratio of gold when the pretreated ore was subjected to ultrasound leaching. The results showed that the appropriate acoustic power was a requirement during the ultrasound-intensified leaching. The leaching ratio of gold increased with an increasing of NaCN concentration from 6 to 18 kg/t. The results demonstrated that the ultrasound is a viable extractive metallurgy technique in pretreatment and leaching for the refractory gold ores.
  • Non-Contact Measurement of Thermophysical Properties of Fe, Fe–C, and Fe–C–Mn Alloys in Solid, Supercooled, and Stable Liquid Phases

    pp. 719-722

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    DOI:10.2355/isijinternational.ISIJINT-2015-526

    High temperature thermophysical properties of Fe and Fe alloys with small additions of C and Mn are reported using electrostatic levitation, for the first time. Thermophysical property measurements were carried out in wide temperature ranges from 800 K to 1850 K, including solids, supercooled, and stable liquids. The small additions of C and Mn affect transformation temperatures, but not significantly other thermophysical properties, i.e., density, volume expansion coefficient, and specific heat. Anomalous volume expansion coefficient was observed in δ-phase.

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