Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 82 (1996), No. 9

  • Influence of Matrix Strength and Pore Structure on Sinter Cake Strength

    pp. 719-724

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    Theoretical and experimental studies were carried out to understand the effects of matrix strength and pore structure on the tensile strength of the sinter cake.
    The matrix strength was described in terms of mass percentage of calcium-ferrite and amorphous silicate. The influence of pore structure on the tensile strength of the sinter cake was determined by the porosity and the pore size distribution. The calculated tensile strength by this model was in good agreement with the observed one.
    As a results of the theoretical studies and the survey of the sinter cake in the sinter plant, it follows that the contribution of the pore size distribution on the sinter yield is about 60%. It is effective to control the pore size distribution, in other words, to decrease the pores above 1.0mm for the improvement of the sinter yield at the top of the sintering bed.
  • The Characteristic of a Thick Slag Layer and Mechanism of Reduction of Iron Ore in the Smelting Reduction

    pp. 725-730

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    It was reported that the reduction rate constant of iron are increased with increasing of the amount of slag in the smelting reduction with a thick slag layer. However, its mechanism was not clear.
    In this study, distributions of metal droplets and carbonaceous materials in the slag layer were investigated with a 100t converter and the mechanism of reduction of iron are was discussed. The obtained results were as follows:
    (1) Considered from the distributions above, 44% of iron oxide was reduced at the metal surface in the lower 30% of the slag layer, 6% of theat was reduced at the metal surface in the upper 70% of the slag layer and 50% of that was reduced at the surface of the carbonaceous materials in the slag.
    (2) For achieving high productivity keeping high post-combustion ratio, low dust formation and a stable operation without slag foaming, the following methods are useful.
    (i) keeping a large amount of slag.
    (ii) keeping a large amount of carbonaceous materials in the slag.
    (iii)controlling the bottom stirring to surpress the amount of metal droplets in the upper 70% of slag layer.
  • Development of One-dimensional Mathematical Model for Pulverized Coal Combustion Considering Particle Dispersion

    pp. 731-736

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    A one-dimensional mathematical model of pulverized coal combustion in a blast furnace considering particle dispersion has been newly developed. On the basis of the model, the combustion efficiency was precisely estimated by setting the dispersion parameters properly for the lance structure. Evaluation of the effect of lance structure on the combustion behavior using this mathematical model suggested that the combustion efficiency in the raceway was greatly improved by intensifying the dispersion of particles. It was estimated that this phenomenon was resulted from the increase of the gasification rate of char particles caused by heating-up and the pyrolysis of the coal particles followed by the combustion of the volatile matter with peripheral oxygen. Moreover a simulation using an oxy-coal lance was carried out. The oxygen supplied from the lance tip was rapidly mixed with the hot blast as coal particles were dispersed, and concentration of oxygen that contributes to coal combustion decreased soon after injection. Therefore, injection of pulverized coal with the oxy-coal lance showed little improvement in combustibility compared with a normal single lance.
    In conclusion, taking the particle dispersion into account in the one-dimensional model, it became possible to make a quantitative approach to evaluate the effect of lance structure, lance arrangement and the manners of oxygen enrichment in an actual blast furnace.
  • Liquid Holdup and Electric Resistivity in an Irrigated Packed Bed

    pp. 737-742

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    Liquid holdup and electric resistivity in an irrigated packed bed for scrap melting with a high-frequency induction furnace was examined by using model experiments. In the measurement of liquid holdups, the contact angle between liquid and particles in the packed bed was controlled above 90°, and the inner wall of the packed bed was lined with a sheet of regularly arranged hemispherical convexity for eliminating wall effect. In the measurement of electric resistivity, molten wood's metal was irrigated to packed beds of graphite or iron particles. As the results, two empirical formulate were obtained as follows;
    For static and dynamic holdups
    εl, s=0.181Cpm-0.458Gam-0.0218, εl, d=1.58×105Rem0.268Cpm-2.16Gam-0.526
    For electric resistivity
    ρe=1.92[1/3(εssll)+2/3 1/εsρslρl]-0.819[Nεs/dp/Lexp(εs-1/εl)]-0.243
    x

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  • Effect of Oxygen Flow Rate and Pressure on Metallurgical Characteristics in Bottom Blowing Converter

    pp. 743-748

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    In order to improve the refining characteristics in the bottom blowing converter (Q-BOP) at Chiba works, the oxygen flow rate at the final stage of the blowing was decreased by reducing the diameter of the bottom tuyere.
    The results obtained are summarized as follows:
    (1) By lowering the oxygen flow rate at the final stage of the blowing, the improvement in the decarburization efficiency is achieved. Consequently, (T.Fe) in slag is lowered.
    (2) The effect of the dilution of the partial pressure of CO, Pco, on the metallurgical characteristics is small in Q-BOP. Therefore, for the improvement in the metallurgical characteristics the reduction of the oxygen flow rate is better than the mixed gas blowing.
    (3) The increase in the pressure of the oxygen gas improves the decarburization efficiency at the same gas flow rate.
    (4) On the basis of the mass transfer model considering the turbulent theory, the mass transfer rate in the reaction zone is assumed to be increased with the increase in the gas pressure. The improvement in the decarburization efficiency by the increase in the gas pressure in Q-BOP is well described by this increase in the mass transfer rate in the reaction zone.
  • Influence of Molten Steel Flow on Inclusion Behavior near the Solidification Shell

    pp. 749-753

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    In in-mold electromagnetic stirring (EMS), horizontal flow is generated by Lorenz force so that non-metallic inclusion entrapment is avoided. Though the effect of EMS is popular by many reports, there are few studies about the behavior of non-metallic inclusions near solidfied shell under horizontal flow. In this study, a model experiment using water and particles made of ion-exchange resin is performed to analyze relations between behavior of non-metallic inclusions near solidified shell and horizontal fluid. As a result of the model experiment, it is cleared that the main factor avoiding nonmetallic inclusion entrapment is the force given by the horizontal flow and that influence of Saffman force can be negligible.
  • Effect of Organic Film Composition on Performance of Organic Composite Coated Steel Sheet with Excellent Lubrication

    pp. 754-759

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    There is an increasing demand for steel sheet that should be completely free from oiling and degreasing during the forming operation in order to improve working environment and hence global environment; In order to achieve this we studied a lubricated galvanized steel sheet, which has a thin organic film on the chromated upper layer.
    A lubricated galvanized steel sheet requires not only good lubricity but also good resistance to mechanical damage that causes deterioration of surface appearance. The reason why the appearance of the steel sheet deteriorated was investigated by considering that this is caused by sliding and deformation. The draw bead test which simulate both sliding and deformation components of forming process was used as a simulation testing method to study deterioration of the appearance.
    From the point of the improvement of resistance against mechanical damage, an organic film has high level of mechanical strength to reduce powdering by sliding, and has adequate softness that allows the film to follow to the press deformation well. The tensile strength and elongation of various films were also measured. On the basis of the test results, it is concluded that thermosetting polyurethane resin has good mechanical properties to provide excellent surface appearance.
  • Effect of N on the Softness of Continuous Annealed Tinplate

    pp. 760-764

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    Effect of the amount of total and solute nitrogen on the softness of continuous annealed tinplate was experimentally investigated.
    (1) Reduction of total N and lowering the slab reheating temperature are effective on softening.
    (2) Hardness of soft temper tinplate does not depend on total N and slab reheating temperature but on solute N in hot rolled sheets, if other conditions are the same. The smaller the amount of solute N is, the lower the hardness of tinplate becomes.
    (3) T-1 of temper degree requires to keep solute N in hot rolled sheets below about 15ppm.
    (4) The phenomenon of softening due to the reduction of solute N in hot rolled sheets cannot be explained by the reduction of its solution hardening, but by the reduction of its pinning effect to grain growth in annealing and by coarse grain structure of annealed sheets.
  • Relationship between Precipitation Behavior and Creep Property of Stabilizing-treated Alloy 706

    pp. 765-770

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    For Ni-Fe-base superalloy 706, a stabilizing treatment between solution-annealing and age- hardening treatments has been proposed to improve its creep rupture life. The precipitation behavior of Alloy 706 was investigated in the present study and related with creep rupture properties. Samples taken from a gas turbine disk forging were solution-treated at 980°C for 3 h and stabilizing-treated in a range of 780 to 900°C for 1.5 h, followed by the double-aging at 720°C for 8 h and at 620°C for 8 h. Precipitation behavior of these samples was examined by SEM and TEM, and creep rupture tests were conducted at three conditions. Four kinds of intra-granular precipitates were identified : fine γ'-γ" coprecipitates having the core of γ' being overlaid with γ" on its top and/or bottom, large γ'-γ" co-precipitates having the core of γ' being completely covered with γ", large γ' precipitates and fine γ" precipitates. At the grain boundary η was identified and found to be accompanied by a serrated grain boundary and denuded zone. Such precipitation behavior was significantly affected by stabilizing temperature, especially below 840°C, and so was creep rupture property accordingly. It is concluded that the best creep rupture properties are obtained when an optimum combination is established among intra-granular fineγ '-γ" co-precipitates, intra-granular large γ'-γ" co-precipitates, and the inter-granular η phase.
  • Recrystallization Texture and Young's Modulus of Ceramic Particle Dispersed Ferrite Steel Bars

    pp. 771-776

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    Formation behavior of recrystallization texture of ceramic particle dispersed ferrite steel bars has been studied in order to achieve high Young's modulus. The ferrite steel bars containing high amounts of ferrite stabilizing elements and small amount of fine Y2O3 particles, which were prepared by mechanical alloying and subsequent hot-extrusion, exhibits considerably high recrystallization temperatures. By the recrystallization at temperatures around 1625K, extremely strong <111> texture is formed. As a result, the Young's modulus in the extrusion direction reaches 282GPa, which is just below the theoretical value of 284GPa. The recrystallization temperature to achieve strong <111> texture depends considerably on the hot-extrusion conditions and amount of ceramic particles. Another texture formation such as <311> by the annealing at higher temperatures will also be discussed.
  • Effects of Ni and Si on Delayed Fracture Properties of High Strength Steels with 1420 MPa Grade

    pp. 777-782

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    Effects of Ni and Si on delayed fracture properties of high strength steels with 1420MPa grade were investigated. 0.25% to 3.5% of Ni or 0.25% to 1.7% of Si was added respectively to 0.3%C-boron-containing steel. Delayed fracture test and measurement of diffusible hydrogen were carried out using bar steels for prestressed concrete with a diameter of 7.1 mm. As each addition of Ni or Si was increased, diffusible hydrogen decreased and delayed fracture properties improved in condition as heat treated. Diffusible hydrogen in Ni-containing steels increased after polishing the surface in comparison with as heat treated and no diffusible hydrogen in Si-containing steels was varied. In Ni-containing steels, Ni concentrating and Ni-sulphide forming at the surface retarded the absorption of hydrogen and delayed fracture properties were improved, while in Si-containing steels, variation of microstructure decreased trapping sites of hydrogen and consequently the absorption of hydrogen was prevented and delayed fracture properties improved.
  • Effects of Strengthening Mechanisms on Fatigue Properties in Hot-Rolled Sheet Steels with Ferrite Matrix

    pp. 783-788

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    This study was carried out with a search for hot-rolled high strength sheet steels having excellent formability and fatigue properties as background. The effects of strengthening mechanisms on fatigue and tensile properties were investigated using hot-rolled TS280880MPa class sheet steels composed of ferrite matrix and harder second phases. The following results were obtained. The improvement of fatigue limit (FL) associated with an increase from 21% to 27% of volume fraction of harder second phases (V2) is small compared with that of tensile strength (TS). The effect of an increase from 260 points to 480 points of the second phase micro-vickers hardness (H2) on FL is also small compared with that on TS. The endurance ratio (FL/TS) has a tendency to decrease as H2 increases. The changes in TS×El and FL×El values with V2 variation are small. The change in TS×El values with H2 variation is small. FL×El values, on the other hand, have a tendency to decrease with the increase of H2. FL/TS and FL/YS (yield stress) increase as the volume fraction of ferrite increases from 73% to 100%. The following empirical formula are proposed from a least squares analysis to estimate FL. FL (MPa)=10, 4×d-1/2+51×(%Si)+16×(%Mn)+80
  • Thermal Conductivities of SUS304/PSZ Composite Materials

    pp. 789-794

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    The effective thermal conductivity and thermal anisotropy of SUS304/PSZ composite materials produced by three different sample preparation processes have been systematically determined by the laser-flash method in the temperature range from room temperature to 1280K. The results obtained are summarized as follows. 1) The thermal conductivity of SUS304/PSZ composite materials increases with increasing the volume fraction of SUS304. 2) Temperature dependence of thermal conductivity of SUS304/PSZ composite materials also changes with increasing the volume fraction of SUS304. This is attributed to the thermal properties of the components of SUS304(positive) and PSZ (slightly negative). 3) Samples having small fractions of pore show higher thermal conductivity values. 4) The thermal anisotropy is not observed in the samples prepared by sintering at atmospheric pressure. On the other hand, the thermal anisotropy is clearly found in the samples prepared by sintering at 20 MPa. This would be attributed to the preferential orientation of PSZ particles in the direction perpendicular to the direction of applied pressure. 5) Estimation for thermal conductivity values has also been made using the equivalent inclusion method in the composition range with relatively low concentration of dispersed phase, because it is difficult to apply this method to the sample where direct contact between dispersed phases is realized. Fair agreement between the estimated and experimental values was found.
  • Thermal Diffusivity Measurements of Fe1-xO by the Devised Laser-Flash Method for Small Samples

    pp. 795-797

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