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

Tetsu-to-Hagané Vol. 86 (2000), No. 3

  • Influence of Iron Ore Properties on the Flow of Melt Formed in the Sintering Process

    pp. 139-145

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    Melt formation and its flow are essential phenomena to proceed agglomeration in the sintering process of iron ores. A new experimental technique have been proposed which enables us to detect the macroscopic flow of melt initially formed by the reaction between iron ore and limestone. Using this technique, influence of iron ore property on the melt formation and assimilation process were examined in terms of meltdown temperature, chemical composition of dropped melt and shape change of a tablet sample. As a result, a difference was obtained in the melt-down behaviors between hematite and pisolitic ores. However, the hematite and pisolitic ores both having a similar gangue mineral composition show similar melt-down temperatures. A pisolitic ore having relatively high Al2O3content has little dependency of particle size and shows higher melt-down temperature. The effect of increase in Al2O3content is considerably large, and it leads to decrease in fluidity of formed melt and increase in melt-down temperature.
  • Hybrid Control of Surface Behavior on Molten Metal by Mold Oscillation and Intermittent Alternating Magnetic Field

    pp. 146-151

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    In a continuous casting of steel, the surface quality of a slab is strongly influenced by mold oscillation. Recently, a new idea in which the imposition of an intermittent alternating magnetic field was synchronized with the mold oscillation has been proposed for the improvement of surface quality under a concept of "soft contacting solidification". The concept is based on the information that the reduction of the contact pressure between a mold and a melt under the imposition of an alternating magnetic field results in good surface quality. However, the most suitable timing for the imposition of the magnetic field in a mold oscillation cycle still has not been determined. To clarify the behavior of the surface wave motion, which is closely related to the contact pressure between a mold and a melt, we have conducted a model experiment on the free surface motion of a molten gallium excited by the synchronous imposition of the intermittent alternating magnetic field and the simulated mold oscillation. The phase difference between the mold oscillation and the magnetic field has been studied from the viewpoint of the suppression of the surface motion. It has been found that the wave shape excited by the synchronous imposition agrees with the numerical superposition of the two wave shapes excited independently by the magnetic field and the mold oscillation, except for the case where a small surface excitation is observed.
  • The Behavior of Argon Gas Bubbles at Meniscus in Continuous Casting Mold

    pp. 152-159

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    The behavior of argon gas bubbles at meniscus in the continuous casting mold was studied using a Wood's metal model. Argon gas was injected into Wood's metal flow through a porous plate or an orifice set in the immersion nozzle. Both the diameter and the number of argon gas bubbles generated at meniscus regions were measured with a color high-speed video camera. Generation rate of argon gas at each region of meniscus was measured with a mass flow meter. The distribution of argon gas bubbles at meniscus was dependent on the flow rate of argon gas injected into the immersion nozzle, but was independent on the flow velocity of Wood's metal in the nozzle. The number of argon gas bubbles at meniscus was dependent on the diameter of bubble. The ratio of the number of argon gas bubbles at meniscus in a unit time was estimated as the following function of bubble diameter.
    n=Ωd-5.5
    where n is the ratio of the number of argon gas bubbles at meniscus in a unit time, Ω is the constant and d is the diameter of argon gas bubble.
    The flow velocity of Wood's metal at meniscus in mold was influenced by the injection rate of argon gas into the immersion nozzle.
  • Development of Emissivity Compensated Pyrometer Using the Information of Reflection

    pp. 160-165

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    The emissivity change due to oxidation is very important information to measure accurate temperature by a pyrometer in steel making process, for example continuous annealing line of cold rolled steel. We have measured the behavior of spectral emissivity in detail during oxidation process. The behavior is very complex and it is difficult to compensate for change in emissivity. In order to compensate for emissivity in steel making process, we have proposed a new method. This method depends on both Kirchhoff's law and the characteristics of surface reflection of cold rolled steel. We have measured surface reflection of cold rolled steel sheets which had three kinds of surface roughness. The angular distribution of reflection mostly concentrates in a normal direction even with the roughest surface steel. 85-93% of hemispherical reflection is measured by reflection from normal to 35 degrees. Emissivity can be accurately estimated by measurement of reflection intensity from steel sheet surface.
    We have manufactured a compact and practical pyrometer, in which specular and diffusive reflection components have been measured by photodiode separately. The accuracy of emissivity is ±13%, and the accuracy of temperature is ±10°C with the temperature range of 650-900°C in both laboratory experiments and continuous annealing line.
  • Determination of Chromium in Iron and Steel by Adsorptive Stripping Voltammetry with Diphenylcarbazide

    pp. 166-170

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    A sensitive and selective method is described for the determination of chromium at the low ppm level in iron and steel by differential pulse adsorptive cathodic stripping voltammetry with diphenylcarbazide as complexing agent. The complex of chromium(VI) with diphenylcarbazide, Cr(III)-diphenylcarbazone, was adsorbed on a graphite electrode for 5 min with open circuit in a nitric-sulfuric acids mixture solution containing phosphoric acid (pH=ca. 0.6), and subsequently was stripped in another solution (the acid mixture solution in the absence of iron(III) and phosphoric acid) in the potential range 0.3 to -0.1V vs. SCE at a scan rate of 50mV/s. Most of the foreign metals did not interfere by application of the non-electrolytic accumulation step. The calibration curve was linear over a concentration range 9.6×10-8to 1.3×10-6M of chromium (correlation coefficient>0.999) and passed through the origin. The detection limit (3σ) was 2.7×10-8M (1.43ngCr(VI)/ml) for an accumulation time of 5min. The determination of 8 to 500 massppm of chromium in iron and steel was achieved with good precision and accuracy within 1 h by the proposed method without any separation of the matrix. The simple method developed can be also applied to the determination of chromium in obsolete steel scrap.
  • Variations of Biaxial Orientation of Polyester Film on Laminated Steel in the Laminating Process

    pp. 171-175

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    Polyester film laminated steel for can container will gradually replace lacquer coated steel sheet from environmental consideration and cost reduction. The process is characterized by partial melting of the film on the steel surface during lamination by pressing the supplied films between both sides of heated steel and a couple of cooled rubber rolls.
    At present, most of polyester films used for the can containers are biaxially oriented films and various characteristics of film laminated steel for can use are strongly influenced by the degree of biaxial orientation of the laminated film.
    Therefore, this report deals with the result of an experiment regarding variations of the degree of biaxial orientation with several polyester films, and thermal analysis of these polyester films by means of Differential Scanning Calorimeter (DSC).
    Finally, from these experiments, we found that it is possible to estimate the variation of the degree of biaxial orientation during lamination by means of thermal analysis.
  • Effect of Pb on the Electrodeposition Behavior of Zn-Ni Alloy

    pp. 176-180

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    The effect of Pb in the bath on the electrodeposition behavior of Zn-Ni alloys in sulfate type baths was investigated for the hydroxide suppression mechanism. In the presence of Pb in the bath, the transition current density where codeposition behavior changes from normal type to anomalous type was increased. This increase can be explained by the following two factors, one is the current density which is equal to reduction rate from Pb2+ ion to Pb as metal, another is the increase of apparent current density because of rough deposits on the electrode surface. The Ni content in deposits increased in the region II where anomalous type codeposition occurred with high current efficiency. This phenomenon appears to have been caused by the metal Pb electrodeposition continuously supplying activation sites for electrodeposition of Ni, which is not blocked in Zn hydroxides, thus accelerating the rate of electrodeposition of Ni, compared to that of Zn.
  • Mechanical Properties of Beta Solution Treated and Aged Ti-10V-2Fe-3Al Alloy

    pp. 181-188

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    Generally Ti-10V-2Fe-3Al and Ti-6Al-4V alloys are solution heat treated below beta transus for use in order to avoid beta grain growth. But recently it was found that beta solution treated and over aged Ti-6Al-4V alloy has martensitic microstructures and good mechanical properties such as high fracture toughness and large crack propagation resistance. The effect of beta solution treatment on the mechanical properties of Ti-10V-2Fe-3Al have been hardly reported. In this study, the mechanical properties of beta solution treated and aged Ti-10V-2Fe-3Al was investigated and compared to conventional solution treatment. Then it is revealed that beta solution treatment gives better fracture toughness and crack propagation resistance comparing with alfa+beta solution treatment.
  • Behaviour of Dislocation Substructures during High Temperature Creep of High-Cr Ferritic Steels

    pp. 189-195

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    The creep behaviour of martensitic 9% chromium steels and the steels alloyed with Mo and W was investigated at temperature of 600 to 650°C under stress of 238 to 350 MPa. The results showed that the creep curves of these alloys were similar to those observed for martensitic 9-12% chromium steels. The minimum creep rate of εminfor model steels alloyed with Mo and W was one order of magnitude lower than εminin base steel. Also the changes of strengthening factor can be described by the effect of solid solution of Mo and W. The observed substructure revealed that sub-boundaries with well-knitted dislocations were always formed and the subgrain size in steady state was inversely proportional to the applied stress. The subgrain size and the dislocation density within subgrains during creep decreased unequivocally with increasing strain, while the misorientation of subgrains increased monotonically with increasing strain. The rate of coarsening for the subgrains of these alloys, however, was dependent on the solute Mo and W and its concentration. It is suggested that creep of these alloys is controlled by the mobility of dislocations in the subgrains and sub-boundaries under the present experimental condition.
  • Estimation of CO2 Emission during Thermo-mechanical Process and Eco-steel Design of a Mn-Si-C Steel by Microstructural Control

    pp. 196-202

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    The amounts of CO2 emission in the production of several commercial JIS standard steels have been estimated by the MLCA database prepared by Halada et al. Although low alloyed steels show smaller amounts of CO2 emission from their database, the database can not estimate the influence of thermo-mechanical process. Therefore, the change of CO2 emission during thermo-mechanical process has been estimated by the annual data concerning consumption of energies and materials publicized from Japanese steel makers. As a result, the change of CO2 emission related to thermo-mechanical process was estimated to share from 5.1% (minimum) to 7.7% (maximum) of the total amount for production. This change is not negligible but much smaller compared with the influence of increasing the content of alloying elements. By combining the prediction of tensile properties of multi-microstructure steels based on micromechanics and the MLCA database, the Mn-Si-C steels are recommended as a candidate of eco-steels from the viewpoints of excellent tensile properties and low CO2 emission for production.

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