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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 79 (1993), No. 1

  • Progress of DH Vacuum Refining Process in Japan

    pp. 1-9

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  • Materials for Skid Rails in Slab Reheating Furnace

    pp. 10-19

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  • Measurement of Effective Thermal Conductivity of Coke

    pp. 20-25

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    Effective thermal conductivity of coke was measured in the temperature range from 100°C to 1400°C by using the laser flash method. Effective thermal conductivity k of coke increased with a rise of temperature, and decreased with an increase of porosity of coke. The effect of radiation in the pore of coke on the value of effective thermal conductivity of coke was very small. The following equation was obtained for effective thermal conductivity k (W/m·k) as a function of temperature T (K) and porosity ε (-) of coke.
    k= {0.973 + 6.34 × 10-3 (T-273)} (1-ε2/3)
    x

    Readers Who Read This Article Also Read

    1. CO2 Recycling for a Carbon Resource Tetsu-to-Hagané Vol.78(1992), No.8
    2. Reaction Rate of Methane Formation for the Catalyst of Reduced Iron Pellets Tetsu-to-Hagané Vol.78(1992), No.11
    3. Outlook of Kinetic Studies on the Combustion of Pulverized Coal in a Blast Furnace Tetsu-to-Hagané Vol.78(1992), No.8
  • Estimation of Hydroxyl Capacity of Molten Silicates by Quadratic Formalism Based on the Regular Solution Model

    pp. 26-33

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    An attempt has been made to estimate the hydroxyl capacities of some molten silicates by the regular solution model of Lumsden, which has been extensively developed to be applied to slag-metal reactions in steelmaking process by the authors. The slag systems discussed were of Na2O-SiO2, K2O-SiO2, Li2O-SiO2, CaO-SiO2 binaries and CaO-SiO2 -Al2O3, CaO-SiO2-MgO, CaO-SiO2-MnO and CaO-SiO2-P2O5 ternaries. In the present work, it was assumed that the water vapor is dissolved in the slag as HO0.5, and the hydroxyl capacity is redefined as C'OH=XHO0.5/(PH2O/P0)1/2, where, PH2O, P0 are partial pressure of water vapor in the gas phase and the atmospheric pressure(Pa), respectively. The interaction energies between hydrogen ion and cation i, αH-ihave been derived based on the regular solution model in the present work. As the result, it has been confirmed that the model has been applicable to predict the hydroxyl capacities over the wide range of slag composition discussed. It has been found that COH calculated by the model showed the minimum value at the slag composition of about unit basicity. The hydroxyl capacities calculated by the model have agreed with the measured within ± 0.002.
    x

    Readers Who Read This Article Also Read

    1. Sulphide Capacities of CaO-Al2O3-SiO2Slags Tetsu-to-Hagané Vol.79(1993), No.1
    2. Mathematical Modelling for Electromagnetic Field and Shaping of Melts in Cold Crucible Tetsu-to-Hagané Vol.77(1991), No.3
    3. O, P and S Distribution Equilibria between Liquid Iron and CaO-Al2O3-FetO Slag Saturated with CaO Tetsu-to-Hagané Vol.77(1991), No.3
  • Sulphide Capacities of CaO-Al2O3-SiO2Slags

    pp. 34-40

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    The sulphide capacities of CaO-Al2O3, CaO-Al2O3-MgO and CaO-Al2O3-SiO2 slags were studied at 1823 to 1923K to estimate the sulphur distribution ratio between secondary steelmaking slag and liquid steel.
    From the obtained results, it was confirmed that substitution of MgO or SiO2 for CaO at a given NAl2O3 decreased the sulphide capacities in both systems of CaO-Al2O3-MgO and CaO-Al2O3-SiO2. The evaluated maximum values of sulphur distribution ratio for both slags were higher than 1000 at 1873K on the condition of CaO-saturation if the dissolved aluminium content in steel was assumed to be 0.01mass%.
  • Metallurgical Characteristics and Optimum Casting Conditions on VADER Process

    pp. 41-47

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    The VADER (Vacuum Arc Double Electrode Remelting) process introduced by Special Metals Corp. in 1982 is a noticeable new vacuum melting and casting technology. This process has potential as an alternative for powder metallurgy in superalloy production, because the as cast VADER ingot might be forged directly due to the uniform fine grain structure and low level of macro-segregation.
    Metallurgical characteristics of VADER process such as formation mechanism of molten metal droplets, optimum casting conditions and hot workability of as cast ingot were studied by melting and casting stainless steel and Ni-base superalloy using an experimental VADER equipment.
    Fine grain structure of 100-200 μm free of micro void was obtained under conditions of low super-heat of molten metal droplets (1030°C) and low casting speed (several cm/min) in the case of 90200mmφ ingots cast into steel molds. The hot workability of as cast Ni-base superalloy ingot was equal to that of forged material.
  • Characterization of Oxide Layers on SUS304L Stainless Steel by Raman Spectroscopy

    pp. 48-54

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    Raman spectroscopy was applied to the characterization of the thin oxide layers produced on SUS304L stainless steel in Ar gases of several purities at 1273K andit was revealed that measurement of the incident angle dependency of Raman spectra from oxide layers makes it possible to identify the outer and inner regions of the two oxide layers on SUS304L. The oxide layer, produced in high purity Ar gas at 1273K-120s, consisted of MnCr2O4spinel type oxide. The oxide layer produced in 99.5%Ar + 0.5%O2 gas showed a double-layer structure, and the outer and the inner were identified with FeCr2O4 and Cr2O2 respectively. The frequency shift of Raman spectra from the powder standards has been shown to be induced by the compressive stress in the oxide layers on stainless steel, and the amount of compressive stresses was estimated.
  • Mechanism of Film-Boiling Onset in Transient Cooling Process with Highly Subcooled Water and Unstable Boiling-Cooling Phenomena

    pp. 55-61

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    The unstable boiling-cooling phenomena in transient cooling process of hot steel bring about dispersion in steel temperature during cooling with subcooled water.The dispersion phenomena of cooling curves are resulted from co-existence of film and transition boiling on the cooling surface of steel in earlier period of cooling. This paper discusses the mechanism of this phenomena in terms of the cooling-curve shape and the average cooling rate in the film boiling region.
    It has been made clear that the unstable boiling-cooling phenomena are not random but have a kind of regularity. The quench point temperature and average cooling rate immediately after the quench point are determined only by the average cooling rate in film boiling region, which is inversely proportional to the thickness of vapor film.
    For the transient cooling process of steels with highly subcooled water, it is suggested that the onset condition of film boiling depends on the roughness because the cavities on the steel surface have a great influence on the capability in trapping air in the bottoms of cavities. The onset of film boiling, namely, depends on the combined effect of geometry and wettability of the cavity wall. The mechanism of unstable boiling cooling can also be understood based on the initiation of film boiling.
  • Development of Rolled Titanium Clad Steel Sheet Using Liquid Phase in the Interface of Both Metals for Joining

    pp. 62-68

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    A technique for hot rolling of the titanium clad steel sheet in atmospheric condition has been newly developed.
    The titanium and steel sheets are assembled in the atmosphere through the copper sheet as insert metal between them. When such clad steel assembly is heated to high temperature, intermetallic compounds of titanium and copper are formed and melted in the interface. The air bubbles and oxides generated in the interface, are squeezed out from the interface with the aid of the melted intermetallic compound and compressive rolling pressure during hot rolling which results in the metallurgical bonding of clean metal surfaces of titanium and copper. On the other hand, copper sheet and steel can be easily bonded because of unstable oxides of both metals. In this technique, the most suitable heating temperature and time for the better bonding properties are 850 to 900°C for 300 to 1800 seconds. Titanium clad steel sheet manufactured using this technique shows approximate 180 MPa of shear strength. Such titanium clad steel is thought to have satisfactory performance with practical use although its bonding strength is relatively lower than those of conventional titanium clad steel manufactured in vacuum condition.
  • Protective Rust Layer Formed on Weathering Steel by Atmospheric Corrosion for a Quarter of a Century

    pp. 69-75

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    The rust layers formed on weathering and mild steels by atmospheric corrosion in an industrial region for a quarter of a century have been characterized by means of observation of the reflection behaviour of polarized light, scanning electron microscopy, infrared transmission, X-ray diffraction and Raman spectroscopy, and electron probe microanalysis.
    It was found that the protective and stable corrosion product which covered the surface of weathering steel mainly consisted of α-FeOOH (ferric oxyhydroxide). The protective rust layer contained a considerable amount of Cr, and was composed of densely packed rust particles in contrast with the rust layer formed on the mild steel. The fact that the protective rust layer was mainly composed of α-FeOOH can reasonably be interpreted in terms of the transformation process of a corrosion product formed by the atmospheric corrosion of steels.
  • Bake Hardenability of Cold Rolled Ti-Bearing Extra Low Carbon Steel Sheets due to Precipitation Control

    pp. 76-82

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    Bake hardenability (BH) of cold rolled titanium-bearing extra low carbon steel sheets has been investigated by examining the precipitation behavior of sulfides and titanium-compounds in hot bands with varying sulfur and manganese content. In high sulfur steels (0.0050mas%) without manganese, Ti4C2S2 mainly precipitated in hot bands, while through the addition of manganese MnS was promoted to precipitate before the Ti4C2S2 precipitation and consequently titaniumcompounds mainly consist of TiN and TiC in hot bands. On the other hand, in low sulfur steels (0.0015mass%) TiN and TiC mainly precipitated independenly of manganese addition. As the solubility temperature of Ti4C2S2 is higher than that of TiC, in an usual continuous annealing temperature range, Ti4C2S2 does not dissolve and consequently carbon in solution does not exist while carbon is dissolved from TiC during annealing, which provides the bake hardenability for annealed sheets.
    Through the precipitation control the BH of 30MPa is achieved for titanium bearing extra low carbon steel sheets with an elongation of greater than 50% and a r-value of higher than 2.0 after annealing.
  • Precipitation of NbC during Hot Strip Production Process

    pp. 83-89

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    The precipitation of NbC during hot rolled steel production process was examined by the laboratory simulation for Nb-bearing low carbon steels.
    For a 0.03%C-0.1%Mn-0.13%Nb steel, finely dispersed NbC precipitates and the precipitate free zone (PFZ) were observed in the ferrite matrix. On the other hand, for the Mn and B bearing steel the NbC precipitaion was suppressed considerably. However by aging treatment in a temperature range between 550 and 700°C the fine precipitates became visible and in the specimens aged at 700°C PFZ was also observed. The addition of Mn and B was also found to lower the austenite/ferrite transformation temperature.
    The suppression of the precipitation by Mn and B addition is explained by the effect of these elements on the transformation temperature, not by the effect on the Nb diffusion rate and solubility product in ferrite.
    The formation of PFZ is explained as follows:
    The coarse particles already precipitate in rows along austenite grain boundaries and deformation bands. Through the austenite/ferrite transformation, the coarse particles grow rapidly and the amount of Nb in solution in the neighborhood decreases, resulting in the formation of PFZ along the rows of the coarse particles.
  • Effects of Alloying Elements and Shot Peening on Impact Fatigue Strength of Carburized Steels

    pp. 90-97

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    Impact fatigue tests were carried out using various kinds of carburized steels. It was shown that internal oxidation was remarkably reduced with decreasing Si and Mn contents, and resulted in higher impact fatigue strength. The effects of residual stress, retained austenite, hardness near the surface, and fatigue fracture toughness were investigated. The difference of the fatigue strength in various carburized steels could be explained in terms of those effects.
    The effect of shot peening application to carburized steel was investigated using JIS standard type steels. As a result, high cycle impact fatigue strength increased 40 to 60% gain by shot peening. This improvement was caused by increase of hardness near surface and compressive residual stress. On the other hand, low cycle fatigue strength showed no gain. For this phenomenon, it was suggested that decrease of the amount of retained austenite by shot peening showed negative effect for fatigue strength. Further, the difference of the fatigue strength in shot peened steels was very slightly. For this reason, it was considered that the life of shot peened steel was influenced by releasing its compressive residual stress rather than the effect of alloying elements.
  • Room Temperature Creep Behavior of Stainless Steels

    pp. 98-104

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    Room temperature creep behavior has been investigated for typical stainless steels (SUS304, SUS430, SUS410L). The mechanism of creep is discussed in comparison with creep data on a carbon steel (SM400).
    The results are summerized as follows:
    1) Stainless steels showed creep deformation at a stress around 0.2% proof stress. Though creep rate decreased monotonously with increase in time, deformation did not ceased even at a time 1000 h. The creep curve of SUS304 steel followed a logarithmic creep law.
    2) No creep was observed in steel SM400 below a critical strain rate at around 10-8S-1.
    3) The facts that interstitial free steels showed room temperature creep, and that SUS304 steel showed no creep at 300°C suggest that the suppression of creep can be attributed to the dynamic strain aging due to the interaction between dislocation and interstitial carbon and nitrogen atoms.
    x

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    1. Effect of Strain Rates on Strength of Sheet Steels Tetsu-to-Hagané Vol.83(1997), No.11
    2. Stress Relaxation Behavior of SUS630 Stainless Steel at Room Temperature Tetsu-to-Hagané Vol.85(1999), No.3
    3. Relationship between Room Temperature Creep Behavior and Yield Strength in Austenitic Stainless Steels Tetsu-to-Hagané Vol.80(1994), No.2
  • Surface Modification by Laser Cladding of Ni-Cr-Al-Y Alloy

    pp. 105-112

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    Ni-22mass%Cr-10mass%Al-lmass%Y (NiCrAlY) alloy, Al, Nb carbide, and Cr carbide added NiCrAlY alloy were deposited on to mild steel substrate using laser cladding. Crack free clad layers were obtained at laser power of 2.5kW, defocus length of 25mm and traverse speed of 5mm/ks.
    Laser clad NiCrAlY alloy and Al added NiCrAlY alloy exhibited superior oxidation resistance because of formation of an Al2O3 protective scale. Spalling of oxide scales reduced the oxidation resistance of laser clad Nb carbide and Cr carbide added NiCrAlY alloy in comparison with NiCrAlY alloy clad layer.
    Wear resistance of laser clad NiCrAlY alloy enhanced after a surface oxidation treatment because of a lubricating effect of the oxide scale. Al addition has no advantageous effect on wear resistance of laser clad NiCrAlY alloy. Laser clad Nb carbide added NiCrAlY alloy has superior wear resistance regardless of the oxidation treatment. Wear resistance of laser clad Cr carbide added NiCrAlY alloy was also improved by the oxidation treatment. However, degradation of the wear resistance did not occur after removing the oxide scale. Thus, the improvement seems to be caused by an effect of carbides precipitated in the clad layer during the oxidation treatment.
  • The Growth of γ' Precipitates in 53Ni-20Co-15Cr Base Superalloy

    pp. 113-119

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    The nucleation and growth behaviors of γ' precipitates in a 53Ni-20Co-15Cr-5Mo-4.9Al-1.3Ti alloy have been investigated mainly by micro-Vickers hardness test, X-ray diffraction analysis and transmission electron microscopy.
    The obtained results are as follows:
    (1) The γ' precipitates were observed to be spherical at the early stage of aging time and to be cuboidal at the later stage.
    (2) The hardness of specimens aged in various conditions closely related to the size and the quantity of γ' precipitates.
    (3) The γ' precipitation cannot be stopped by water quenching after solution treatment. It is necessary to quench the specimen at the rate of over 104K/s to restrain the precipitation of γ' phase.
    (4) The growth kinetics of γ' precipitates in the alloy followed the prediction of Lifshitz-Slyozov-Wagner(LSW) theory of volume diffusion controlled growth at all aging temperatures. The activation energy for the growth of γ' precipitates was estimated to be 266kJ/mol which was nearly similar to those of diffusion of solute atoms; ie. Al, Ti and so on, in Ni and Ni alloys.
    (5) The actual particle size distribution of γ' precipitates was somewhat different from the distribution predicted by the LSW or Brailsford-Wynblatt encounter modified (BWEM) theory.
  • Production and Technology of Iron and Steel in Japan during 1992

    pp. N6-N22

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    x

    Readers Who Read This Article Also Read

    1. CO2 Recycling for a Carbon Resource Tetsu-to-Hagané Vol.78(1992), No.8
    2. Reaction Rate of Methane Formation for the Catalyst of Reduced Iron Pellets Tetsu-to-Hagané Vol.78(1992), No.11
    3. Outlook of Kinetic Studies on the Combustion of Pulverized Coal in a Blast Furnace Tetsu-to-Hagané Vol.78(1992), No.8

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