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

ISIJ International Vol. 49 (2009), No. 12

  • Mathematical Model for Prediction of Composition of Inclusions Formed during Solidification of Liquid Steel

    pp. 1819-1827

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    DOI:10.2355/isijinternational.49.1819

    Non-metallic inclusions originate mainly during secondary steelmaking due to deoxidation and other exogenous sources. Additional inclusions form during cooling and subsequent freezing of liquid steel. Rejection of solutes by the solidifying dendrites causes segregation of solutes in the interdendritic liquid with consequent build-up of their thermodynamic supersaturation. The work reported in the present paper was undertaken to develop a computation procedure for prediction of inclusion compositions formed during cooling and solidification of liquid steel. The model has been applied to an inclusion sensitive grade of steel. Segregation of various solutes with progress of freezing has been calculated using the Clyne–Kurz microsegregation equation. A sequential computation procedure involving segregation equation and thermodynamic equilibrium calculations by the Factsage thermodynamic software has been developed. Compositions of inclusions at various solid fractions have been determined. Model predictions have been compared with literature as well as with inclusion compositions determined in continuously cast billet samples using SEM-EDS. Reasonably good correspondence between model predictions and observed inclusions have been obtained.
  • A Thermodynamic Model for Calculating Sulphur Distribution Ratio between CaO–SiO2–MgO–Al2O3 Ironmaking Slags and Carbon Saturated Hot Metal Based on the Ion and Molecule Coexistence Theory

    pp. 1828-1837

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    DOI:10.2355/isijinternational.49.1828

    A thermodynamic model for calculating sulphur distribution ratio between CaO–SiO2–MgO–Al2O3 ironmaking slags and carbon saturated hot metal has been developed by using a thermodynamic model for calculating mass action concentrations of structural units or ion couples of ironmaking slags based on the ion and molecule coexistence theory.
    The calculated mass action concentrations of structural units or ion couples in CaO–SiO2–MgO–Al2O3 ironmaking slags equilibrated with carbon saturated hot metal at 1773 K can be applied to represent reaction ability, like classic concept of activity. The calculated total sulphur distribution ratio shows an acceptable agreement with the tested sulphur distribution ratio between CaO–SiO2–MgO–Al2O3 ironmaking slags and carbon saturated hot metal from desulphurization experiments at 1773 K. Meanwhile, the developed thermodynamic model for calculating sulphur distribution ratio between CaO–SiO2–MgO–Al2O3 ironmaking slags and carbon saturated hot metal can quantitatively determine the respective contribution of free CaO and MgO in CaO–SiO2–MgO–Al2O3 slags. A very significant difference of desulphurization ability between free CaO and MgO has been found with free CaO accounting for 97% desulphurization potential comparing with free MgO as about 3% in CaO–SiO2–MgO–Al2O3 slags equilibrated with carbon saturated hot metal at 1773 K.
  • Mass Transfer of P2O5 between Liquid Slag and Solid Solution of 2CaO·SiO2 and 3CaO·P2O5

    pp. 1838-1844

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    DOI:10.2355/isijinternational.49.1838

    Hot metal dephosphorization slags in the BOF can be considered to be within the CaO–SiO2–FeO–P2O5 system, and are usually in the dicalcium silicate (C2S) saturated composition range. It is well known that C2S forms a pseudo-binary solid solution with tricalcium phosphate (C3P) over a wide composition range at the dephosphorization treatment temperature. To increase the reaction efficiency of dephosphorization, it is important to increase the mass transfer rate of P2O5 from the liquid slag to the solid solution.
    In order to clarify the mechanism of mass transfer of P2O5 between the solid solution and liquid slag, an artificially made C2S–C3P solid solution rod was dipped into the C2S–C3P saturated slag and the interface was observed.
    When the activity of P2O5 in liquid slag was higher than that in solid solution, a reaction layer was formed at the interface, and its width increased with immersion time. A concentration gradient of P2O5 was observed in the solid solution.
    When the activity of P2O5 in liquid slag was lower than that in solid solution, no reaction layer was formed, and P2O5 did not transfer to the liquid slag. In this case, P2O5 in the solid solution was quite stable.
    The reason for these phenomena was discussed. The mass transfer of CaO and SiO2 must occur simultaneously with the mass transfer of P2O5 in order to maintain the pseudo-binary relation of the solid solution.
  • Theoretical Consideration of Heat Flux Distribution of Arc Driven by AC Magnetic Field

    pp. 1845-1849

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    DOI:10.2355/isijinternational.49.1845

    A magnetically driven arc is produced by imposing an external magnetic field to a transferred arc. Its width is determined by the amplitude of its oscillatory motion. Its heat flux distribution can be controlled by the waveform of the magnetic field. Prediction of the heat flux distribution on the anode is necessary to apply the magnetically driven arc in industrial fields.
    This paper describes the theoretical examination of the magnetically driven arc. A one-dimensional heat source with a Gaussian distribution is assumed to predict the heat flux distribution within the amplitude. First, the heat flux variation according to the magnetic flux density was examined under a DC magnetic field. Based on that investigation, the heat flux distributions in various AC magnetic fields were considered within the oscillatory amplitude.
  • Ti Deoxidation Equilibrium in Molten Fe–Cr and Fe–Cr–Ni Alloys at Temperatures between 1823 K and 1923 K

    pp. 1850-1859

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    DOI:10.2355/isijinternational.49.1850

    Titanium deoxidation equilibria between Ti and O in molten Fe–Cr and Fe–Cr–Ni alloys were investigated at temperatures of 1823 to 1923 K. Titanium oxides equilibrated with molten Fe–Cr and Fe–Cr–Ni alloys have been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). Deoxidation product changes from Ti2O3 to Ti3O5 with decrease of Ti content in Fe–Cr and Fe–Cr–Ni alloys.
    Binary interaction parameters of Redlich–Kister type polynomial between Cr and O was assessed by using the previous experimental result in the Fe–Cr–O system. Experimental result of titanium deoxidation in molten Fe–Cr alloy has been numerically analyzed by the excess Gibbs free energy change of mixing Fe–Cr–Ti–O system with Redlich–Kister type polynomial. Validity of evaluated parameters between Cr–O (ΩCr–O) and Cr–Ti (ΩCr–Ti) was confirmed by comparison with experimental result for Fe–Cr–Ni alloy.
    Binary interaction parameters of Redlich–Kister type polynomial in present work were evaluated as follows,
    0ΩCr–O = −52870−24.10T J/mol (XO<0.0015, 1823≤T≤1923 K)
    1ΩCr–O = −498200+234.7T J/mol (XO<0.0015, 1823≤T≤1923 K)
    0ΩCr–Ti = 365700−206.3T J/mol (XTi<0.003, 1823≤T≤1923 K)
    1ΩCr–Ti = 432900−208.8T J/mol (XTi<0.003, 1823≤T≤1923 K)
    x

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  • Influence of Mineral Matter on Carbon Dissolution from Metallurgical Coke into Molten Iron: Interfacial Phenomena

    pp. 1860-1867

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    DOI:10.2355/isijinternational.49.1860

    Identifying key factors governing the rate of carburisation of liquid iron is important for sustainable developments in blast furnace ironmaking. This study investigated the influence of mineral matter on carburisation rate ‘K’ for two different cokes: coke 1 (K=14.7×10−3 s−1) and coke 2 (K=1.1×10−3 s−1). The sessile drop technique was used to investigate carbon dissolution from coke into molten iron (1450°C, 1550°C) and the nature of interfacial products formed. Examination of the underside of the iron droplets showed the iron/coke interface was markedly different in appearance and composition between the two cokes. The interfacial product formed with coke 2 had a mesh like structure that seemed to wet the iron droplet much better than the interfacial product formed with coke 1. In contrast, Fe globules and discrete interfacial products were observed in coke 1. Interfacial products containing calcium sulfide (CaS) and manganese sulfide (MnS), were observed for both cokes. The presence of MnS could reduce the overall viscosity of the interfacial layer as it's known to lower the liquidus temperature. Electron dispersive X-ray analyses of coke 1 identified iron to be in close association with sulfur. These Fe/S species have atomic ratio similar to pyrrhotite (Fe1−xS) or troilite (FeS). Pyrrhotite in coke can decompose to release gaseous sulfur and metallic iron, which can be carburised to form Fe–C particles. Carburisation of liquid iron can thus occur via Fe–C particles. These factors can have a significant influence on the kinetics of carbon dissolution.
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    1. Effect of Carbonisation Conditions on Mineral Matter in Coke ISIJ International Vol.47(2007), No.1
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    3. Effects of Coal Inertinite Size on Coke Strength ISIJ International Vol.48(2008), No.5
  • Carbon Dissolution Occurring during Graphite–Ferrosilicon Interactions at 1550°C

    pp. 1868-1873

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    DOI:10.2355/isijinternational.49.1868

    The carburisation reaction is a key reaction for the cupola process, since the metallic liquid droplets interact with coke at high temperatures. The kinetic mechanism of carbon dissolution in liquid iron had been extensively investigated. However, there is little knowledge about the kinetics of carbon dissolution when the silicon contents are over 10%, since the silicon content during the iron and steel making processes are usually well below this limit.
    Carbon dissolution phenomenon and associated mechanisms are established for ferrosilicon alloys and silicon at 1550°C in this study. The overall-rate constants at 1550°C for Si 98.5%, FeSi 74% and FeSi 24.7% were 3.8, 3 and 3.9×10−3 (s−1) respectively. The appearance of SiC as an interfacial product was found during the metal–graphite interactions and its role as a retarding agent during the carbon pickup was established.
    The kinetics of carbon dissolution from graphite is controlled by a mixed-control mechanism and this includes the diffusion of carbon and carbon transfer from the SiC interfacial layer.
  • Removal Behavior of Zn, Pb, K and Na from Cold Bonded Briquettes of Metallurgical Dust in Simulated RHF

    pp. 1874-1881

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    DOI:10.2355/isijinternational.49.1874

    Removal behavior of Zn, Pb, K and Na from cold bonded briquettes made by mixing four typical metallurgical wastes, as blast furnace dust, converter dust, electric arc furnace dust and converter sludge with proper proportions, in a simulated RHF (Rotary Hearth Furnace) were investigated in this paper. Effects of temperature and C/O molar ratio on metallization rate of iron oxides, and effect of temperature on removal rate of elements Zn, Pb, K and Na were checked respectively. The results show that when reduction temperature, C/O molar ratio, reduction time are 1300°C, 1 and 15 min respectively, removal rates of Zn, Pb, K and Na are 97.1%, 99.4%, 94.5% and 89.6% respectively, at the same time the metallization rate is 80.6%, which can meet demands of the blast furnace. X-ray mapping analysis via scanning electron micrograph (SEM) for Zn, Pb, K and Na in the cold bonded briquettes at different reduction time and different selected areas tells that Zn, Pb, K and Na located in edge of the briquettes remove faster than those located in the center of briquettes. The dust arrested in the reduction process, called as secondary dust, is proved to be mixture of mainly Zn, ZnO, KCl and NaCl by X-ray diffraction (XRD) analysis and SEM EDS (energy-dispersive spectrometry), and contents of Zn and KCl are obtained as over 60% and nearly 20% respectively, while Pb is probably in an insufficient amount to be detected. Water leaching tests arrive at a conclusion that primary separation of Zn and Pb from K and Na is obtained as expected, meanwhile content of element Zn increases from 57.9% in the initial secondary dust to 73.6% as ZnO in the leaching residual.
  • Electrochemical Method for Controlling the Interfacial Oxygen in Molten Fe with ZrO2 Based Solid Electrolyte

    pp. 1882-1888

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    DOI:10.2355/isijinternational.49.1882

    The control of the interfacial oxygen concentration in molten steel by an electrochemical method using ZrO2 based solid electrolyte was suggested in this study. Oxygen ions were transferred through the solid electrolyte by varying the chemical potential difference and applying an external electric potential between the cathode and the anode. By applying an external electric potential, the oxygen concentration was controlled below 3 ppm at the molten Fe/ZrO2 interface. The electrochemical reaction rate of oxygen removal was found to be faster than the estimated diffusion of oxygen through the boundary layer of molten steel. Thus, the slow diffusion of oxygen through the boundary layer creates a steady state oxygen concentration profile, where an oxygen depleted layer at the molten Fe/ZrO2 interface is present. The oxygen concentration profile in the boundary layer was confirmed using the Glow Discharge Spectroscopy.
    In this study, the oxygen concentration at the interface could be controlled using an electrochemical method of ZrO2 based solid electrolyte and achieve a steady state at the interface within the liquid phase boundary layer.
  • A Novel Bottom Stirring Scheme to Improve BOF Performance through Mixing and Mass Transfer Modelling

    pp. 1889-1894

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    DOI:10.2355/isijinternational.49.1889

    In combined blown basic oxygen steelmaking converter bottom stirring plays an important role in mixing within the bath. Better mixing within the bath and improved mass transfer between slag and metal is believed to cause better dephosphorisation. Normally an equal amount of gas in passed from each tuyere in bottom stirring throughout the blow. Here a novel bottom stirring scheme has been proposed and investigated where different amount of gas was injected from different tuyeres in last 3 to 5 min of the blow. The investigation was carried out with respect to mixing and mass transfer in a scaled-down physical model having appropriate similarity with the actual steelmaking vessel. The scheme, differential flow bottom stirring, basically redistributes the total bottom gas flow in a manner so that a linear flow gradient is imposed across the bath. It was found that the differential flow bottom stirring scheme gives 30–35% improvement in mixing compared to uniform flow through all the bottom tuyeres. The scheme also gave better mass transfer rates than the conventional stirring. A 30% increase in the mass transfer rate was observed. Plant trials with the scheme were conducted to assess the impact on dephosphorisation within the practical BOF vessel. Improved BOF performance in terms of phosphorous removal was obtained in the plant trials. Comparatively lower turn-down phosphorous and improved phosphorous partition was achieved with a saving in bottom gas injection amount.
  • Parametric Investigation of Interfacial Heat Transfer and Behavior of the Melt Puddle in Planar Flow Casting Process by Numerical Simulation

    pp. 1895-1901

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    DOI:10.2355/isijinternational.49.1895

    The interfacial heat transfer between a rotating roller surface and a melt puddle, and the thermal and fluid-dynamical behaviors of the melt puddle play an important role in the formation of the amorphous alloy ribbon in the Planar Flow Casting (PFC) process. Several parametric studies, including the melt and the roller thermal conductivities, melt inflow temperature, rotating roller speed and melt ejection velocity have been performed to investigate their effect on interfacial heat transfer and on the behavior of the melt puddle by the solution of a conjugated fluid–solid (melt/roller) mathematical model. With the given process parameters, the theoretical interfacial heat transfer and interfacial temperature, puddle shape, velocity and temperature distribution in the melt puddle, temperature profile of the roller and thermal penetration depth underneath the puddle, and the growth and cooling characteristics of solid/liquid interface are presented and discussed. It is found that the upstream and downstream menisci are sensitive to the variations of these parameters. The casting conditions affect the profile of theoretical interfacial heat transfer coefficient and roller surface temperature. However, the flow patterns in the puddle hardly change except the size of two recirculation zones with stagnate flow. As a result of lower roller speed and larger melt ejection velocity, the thermal penetration depth in the roller and the thickness of the ribbon increase, and the solidification rate reduces during the later period of solidification process. The decrease of roller thermal conductivity will lead to a high roller surface temperature and a low thermal penetration depth. The melt with high thermal conductivity has a quicker growth of the solid/liquid interface. The solidification rates of the solid/liquid interface seem to also be slow near the final solidification stage with the decrease of roller thermal conductivity, and with the increase of melt inflow temperature and melt ejection velocity.
  • Electrochemical and Surface Analytical Approach to Passive Film on 200 Series Stainless Steels Formed in Sulfuric Acid

    pp. 1902-1906

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    DOI:10.2355/isijinternational.49.1902

    Electrochemical corrosion behaviour and chemical structure of the passive film of two newly developed austenitic stainless steels belonging to 200 series were studied in 1 M sulphuric acid (H2SO4). From polarization studies it was found that addition of Cu in the Cr–Mn–Ni stainless steel is beneficial in the passive range in terms of reduction in current density. X-ray photoelectron spectroscopy analysis of the passive film revealed enrichment of Cr ions on the surface irrespective of Ni and Mn content in the alloy. Mn in the passive film was relatively less considering its content in the alloy, but it increases with increase of Mn in the alloy. N compound was also observed in the passive film. Cu was present in the metallic as well as ionic form.
    x

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    1. Mathematical Model for Prediction of Composition of Inclusions Formed during Solidification of Liquid Steel ISIJ International Vol.49(2009), No.12
  • A Numerical Study on the Validity of the Local Equilibrium Hypothesis in Modeling Hydrogen Thermal Desorption Spectra

    pp. 1907-1913

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    DOI:10.2355/isijinternational.49.1907

    We present a systematic benchmark study on different numerical models for analyzing hydrogen thermal desorption spectra, by focusing on the adoption of the local equilibrium hypothesis in these models. We find that the direct numerical method of the full set of the extended mass conservation equations is only able to predict the experimental behavior of thermal desorption spectra for pure iron in the thin specimen limit, while other models incorporating the local equilibrium hypothesis fail to predict this behavior.
  • Characterization of Mechanically Alloyed Powders for High-Cr Oxide Dispersion Strengthened Ferritic Steel

    pp. 1914-1919

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    DOI:10.2355/isijinternational.49.1914

    High-Cr oxide dispersion strengthened (ODS) ferritic steel powders with the nominal composition of Fe–16Cr–4Al–0.1Ti–0.35Y2O3 in wt% were produced by milling of elemental powders and Y2O3 particles in argon atmosphere to investigate changes in the particle properties during mechanical alloying (MA). SEM observation and PSD analysis revealed that the MA powders milled for different times were composed of agglomerated particles having multimodal distributions with substantial size variation ranging from several μm to 350 μm. The mean size of particles rapidly increased at the initial stage of MA, then gradually decreased to 22 μm with increasing milling time up to 48 h, and kept constant thereafter. During milling of the Fe–16Cr–4Al–0.1Ti–0.35Y2O3 powder, MA within 6 h had mainly taken place between Fe and Al to form a bcc-Fe(Al) solid solution. The lattice constant of bcc-Fe steadily increased with a drastic increase in the solute concentrations of Cr, Al, and Ti in Fe. Alloying between Fe and alloying elements is almost fulfilled after milling for 48 h. The MA powder milled in air was much smaller than that milled in gaseous argon under the same conditions. Milling in an air atmosphere is effective to reduce the particle size of the ODS ferritic steel powder, although the pickup of oxygen from environment causes too high excess oxygen content.
  • Role of Surface Roughness in Water Spray Cooling Heat Transfer of Hot Steel Plate

    pp. 1920-1925

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    DOI:10.2355/isijinternational.49.1920

    A water spray cooling has been widely used in a variety of engineering applications. The current study focuses on making quantitative measurements of heat transfer by water spray as it impinges on the rough surface of hot steel plate at higher temperature nominally up to 900°C. The local heat flux measurements are introduced by a novel experimental technique in which test block assemblies with cartridge heaters, thermocouples are used to measure the heat flux distribution on the surface of hot steel plate as a function of heat flux gauge. The roles of surface roughness on heat transfer are presented for well-characterized four rough surfaces with average rms roughness heights ranging from 40 to 80 μm. The results show that the local heat transfer for the rough surface is compared with that for a smooth surface. Finally the heat transfer enhancement mechanism on rough surface can be investigated by the different boiling phenomena.
  • Oxidation Behavior of Pure Copper in Oxygen and/or Water Vapor at Intermediate Temperature

    pp. 1926-1931

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    DOI:10.2355/isijinternational.49.1926

    The oxidation of pure copper in oxygen with and without water vapor was investigated as a function of temperature, oxygen pressure, and water vapor pressure using thermogravimetric analysis. The rate of the oxidation was increased with increasing temperature from 500 to 700°C and followed by the parabolic rate law regardless of the presence of water vapor. The activation energy for the oxidation was 90.67 kJ/mol in dry oxygen and 95.86 kJ/mol in oxygen with water vapor. The change of oxygen pressure without water vapor does not affect the oxidation rate at given temperatures. However, increasing water vapor pressure from 0.39 to 0.58 atm resulted in higher oxidation rate due to the increase of copper vacancies. CuO whiskers were observed and their growth seems to be enhanced by the presence of water vapor.
  • Influences of Morphology and Size of Mg2Si on Microstructural Evolution of Mg–6.2Si Alloys during Partial Remelting

    pp. 1932-1937

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    DOI:10.2355/isijinternational.49.1932

    After isothermally treated at 660°C for 20 min, both dendritic Mg2Si in unmodified alloys and polyhedral ones in KBF4-modified alloys transformed to nearly globular morphology, while the degree of spheroidization in KBF4-modified alloy was lower than that in unmodified alloy. This result might be attributed to both restriction effect of boron and stability of octahedral primary Mg2Si crystals. After isothermal treatment at 660°C for 20 min, however, the initial grain sizes of dendritic Mg2Si crystals in unmodified alloy or polyhedral ones in modified alloy obtained by different cooling rates (copper mold with the holes of φ20 and φ6 mm) only caused a little effect on the partial remelting microstructure. The fine primary Mg2Si particles obtained from φ6 mm hole, however, were more readily to evolve to globular crystals, which might be attributed to the more active Ostwald ripening and/or coalescence.
  • The Effect of S and Mn on the High-temperature Oxidation and Scale Spallation Behavior of Low-carbon Steels

    pp. 1938-1944

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    DOI:10.2355/isijinternational.49.1938

    Early-stage oxidation behavior in air of low-carbon steels with and without S and Mn additions was investigated in terms of oxidation kinetics and scale spallation in a temperature range of 900 to 1150°C. S and Mn did not appear to affect the growth rate of oxide scales within the given oxidation time, ~30 min, however it was found that S significantly enhanced oxide scale spallation. Scale spallation occurred only on the S doped steels oxidized at temperatures more than 1000°C when the thickness of oxide scale exceeded about 120 μm. This scale spallation was confirmed to occur during cooling after the given oxidation time. GD-OES analysis revealed that a significant amount of S enrichment occurred at the oxide/steel interface, which was around 1 mass% on 100 ppm S steel after 120 s of oxidation at 1150°C. Such sulfur enrichment was speculated to be due to accumulation of rejected S from surface recession during the high-temperature oxidation. Observation of the steel surface after complete removal of the oxide scale by quenching the steels into liquid nitrogen clearly indicates the formation of eutectic Fe–FeS structure at scale/steel interface, resulting from a liquid phase formation above 1000°C. Formation of sulfide, and therefore a liquid phase at higher temperature, greatly affected oxide scale spallation.
  • Effect of Heat Treatment on Formability of Hot-dip Galvanized Low Carbon Steel Sheet

    pp. 1945-1951

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    DOI:10.2355/isijinternational.49.1945

    In this research, the effects of annealing heat treatment on the coating microstructure and formability of hot dip galvanized sheet were evaluated. For this purpose, samples of galvanized sheet with identical production parameters, mechanical properties, and coating thicknesses (weight) were heat treated at a temperature range of 500–540°C for 10–180 s. After heat treatment, the samples were cooled in water and dried quickly. Scanning electron microscopy (SEM) was employed before and after heat treatment to evaluate the microstructure and coating layers. Energy dispersive spectroscopy (EDS) microanalyser and x-ray diffractometer were also used to determine each layer's chemical composition and phase, respectively. Formability of the samples was evaluated using forming limit diagrams (FLDs). FLDs and strain distribution were evaluated experimentally by stretch-forming sheet samples over a hemispherical punch. The fractography of the stretched samples was accomplished using SEM. Experimental results show that surface appearance quality changes with temperature and time of heat treatment process from silvery and bright to gray and dull. Conclusions drawn from formability evaluations indicate that the growth of iron-zinc brittle intermetallic layers and complete removal of η phase in heat treatment decrease the level of forming limit diagrams. Also, heat treatment at higher temperatures and for shorter process times improves coating formability behavior.
  • Hydrogen Delayed Fracture Properties and Internal Hydrogen Behavior of a Fe–18Mn–1.5Al–0.6C TWIP Steel

    pp. 1952-1959

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    DOI:10.2355/isijinternational.49.1952

    The hydrogen delayed fracture (HDF) properties and internal hydrogen behavior were investigated in a Fe–18Mn–1.5Al–0.6C steel, a representative twinning induced plasticity (TWIP) aided steel. Slow strain rate tests (SSRT) were employed on both smooth and notched specimens to evaluate the effects of diffusible hydrogen on the HDF properties of the steel. Results showed that the fracture stress, fracture strain and time to fracture of the hydrogen pre-charged specimens were relatively insensitive to the amount of diffusible hydrogen. Fracture surface exhibited a ductile dimple fracture mode regardless of the diffusible hydrogen concentration. It was found that most hydrogen became non-diffusible after SSRT. The major trapping sites of hydrogen were dislocations, grain boundaries and twins. The activation energies for detrapping of hydrogen were estimated 35 kJ/mol for dislocations or grain boundaries, and 62 kJ/mol for twins. A comparison of the HDF properties of the present steel with those of other high strength steels revealed that the TWIP steel appeared to be relatively immune to hydrogen delayed fracture. This was due to the combined effects of (a) higher hydrogen solubility of austenite matrix (b) negligible portion of diffusible hydrogen to the total hydrogen, (c) decrease of diffusible hydrogen content during the deformation, and (d) no transformation of austenite to either ε or α′ martensite.
  • Puddling: A New Look at an Old Process

    pp. 1960-1966

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    DOI:10.2355/isijinternational.49.1960

    Throughout most of the 19th century, the process of choice in the west for producing wrought iron and steel was “puddling” of cast iron. A major development of the process, “wet puddling”, became widespread commercially beginning in 1830. That process is examined quantitatively using modern thermodynamic, solidification and rheologic understanding. The ‘clearing’ and ‘boiling’ steps are considered in detail. In the ‘clearing’ step, the silicon is oxidized (by iron oxide) resulting in bath heating. Subsequent carbon removal from the melt, prior to initiation of solid iron solidification results first in the ‘low boil’, with simultaneous melt cooling. Then, as decarburization continues, solidification of iron begins, and with it, the ‘high boil’, with vigorous gas evolution and significant temperature increase. The importance of the iron solidification in promoting the decarburization reaction has not, in our opinion been fully understood heretofore. The lower the carbon content at the start of the boil, the higher the final melt temperature, and the lower the carbon content in the fully solid iron. During the high boil the four phase slurry of slag, liquid iron, solid iron and gas is thixotropic in nature, readily agglomerates, and possesses a low viscosity up to fractions solid of 0.2–0.3, with that viscosity rising rapidly at higher fractions solid. Comparison of the model presented with observations from the actual puddling process is made. The qualitative and quantitative model presented agrees in general outline with the historical record and serves to strengthen our respect for those master puddlers who could control such a complex process with little other than their senses to guide them.
  • In-use Stock of Steel Estimated by Top-down Approach and Bottom-up Approach

    pp. 1967-1971

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    DOI:10.2355/isijinternational.49.1967

    Recently, prices of natural resources have rapidly risen, so recovery of materials from the end-of-life products as secondary resources is of great interest. However, it is generally a challenging task to estimate the in-use stock of materials, especially in developing countries, because of lack of data. In this paper, two approaches, the top-down approach and the bottom-up approach, were adopted for estimating the in-use steel stock in end uses. The top-down approach uses time-series data of consumption and trade of materials and product lifetime data, whereas the bottom-up approach uses the numbers of units of a specified product in a designated area and its material intensities. In this paper, steel stock in Japan divided into seven end-uses was estimated by the top-down approach. Steel in-use stock in Japan was estimated as approximately 1000 Tg in 2005. Steel stock in automobiles in 2005 was estimated as 105 Tg by the bottom-up approach and compared with that estimated as 125 Tg by the top-down approach. In addition, applying the bottom-up approach, steel stock used in automobiles in the United States was estimated and compared with that obtained by the previous research using the top-down approach. Steel stock used in automobiles in 2000 in the United States was estimated as 480–870 Tg by the top-down approach and 754–767 Tg by the bottom-up approach. Both approaches have some uncertainties in the parameters used in the estimation. Therefore, complementary use of the two approaches is helpful to estimate in-use stock of materials.
  • Strengthening Dual Phase Steel Welds by Shot Peening

    pp. 1972-1974

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    DOI:10.2355/isijinternational.49.1972

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    1. Hydrogen Delayed Fracture Properties and Internal Hydrogen Behavior of a Fe–18Mn–1.5Al–0.6C TWIP Steel ISIJ International Vol.49(2009), No.12
  • Prediction of Annual Production Rate of Crude Steel after the Global Financial Crisis in 2008 by Using the Logistic Transformation Procedure

    pp. 1975-1977

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    DOI:10.2355/isijinternational.49.1975

  • Erratum: Intensification of Bubble Disintegration and Dispersion by Mechanical Stirring in Gas Injection Refining
    [ISIJ. Int. 49(1): 17-23 (2009)]

    pp. 1978-1978

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    DOI:10.2355/isijinternational.49.1978

    Correction of the parameters reported in the paper “Intensification of Bubble Disintegration and Dispersion by Mechanical Stirring in Gas Injection Refining” Yan Liu, Masamichi Sano, TingAn Zhang, Qiang Wang and JiCheng He, ISIJ Int., 49 (2009), No. 1, pp. 17–23.
    The authors have found that the numerical values in Page 22 reported in the above paper are incorrect. The authors would like to correct the parameters as follows:
    [Table]

    This correction does not affect Tables, Figures, other equations, discussion and conclusions in the article at all.

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