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

Tetsu-to-Hagané Vol. 88 (2002), No. 4

  • Advance in the Excitation Source in Glow Discharge Optical Emission Spectrometry

    pp. 169-179

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    A Grimm-style glow discharge is now an important excitation source in atomic emission spectrometry, especially for direct analysis of solid samples. Many studies have been conducted for enhancing the emission intensities from the source and thus improving the detection sensitivity in the analytical applications. This review introduces several improved Grimm-style excitation sources. The techniques employed in such sources include the modification of the source geometry, supplementary discharges caused by d.c. or microwave powers, and methods for controlling the glow discharge plasma. Improvement in the analytical performance is presented when they are compared with a conventional Grimm-style glow discharge source.
  • Mass Transfer Influenced by Wave Motions Appearing on Gas-Liquid Interface Exposed to Turbulent Flow

    pp. 180-187

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    Wave motions appear on the surface of a single-bubble rising in liquid when the bubble Reynolds number exceeds a certain critical value. Such wave motions enhance the mass transfer from the bubble to the liquid especially under the condition that the bubble surface is contaminated by surfactant. This is caused by surface renewal due to the wave motions. The mass transfer coefficient under this condition was experimentally measured using a simplified model. Water and CO2 gas were used as the working fluids. Two empirical equations for the mass transfer coefficient were proposed.
  • Evaluation of Matrix of Coke Strength by Nano-indentation Method

    pp. 188-194

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    Nano-indentation method is proposed to measure the elastic modulus of matrix of coke and to study the relativity of the elastic modulus to raw coal.
    Coke strength is the most important qualities to retain the permeability in a blast furnace. Then coke strength must be clarified. Matrix of coke elastic modulus and its relation to raw coal are essential for theoretical approach based on Mechanics of Materials to reveal the fracture behavior of coke. Nano-indentation method, which couples the equation obtained by finite element analysis with the load-displacement curves in the microscopic region measured by ultra-micro-hardness tester, enables us to determine the elastic modulus of coke substrate except the effect of pores.
    The matrix elastic modules of cokes made from four kinds of coal are measured for each coke texture. Elastic modules of flow texture, coarse mosaic texture and fine mosaic texture that are the texture originated in reactives are 17-18 GPa for every raw coal, so they can be regarded as same strength. The elastic modulus of inerts is higher than that of the textures organized in reactives, and increases as coal rank increases.
    As a result it follows that matrix of coke is simplified to a composite material composed of two kinds of materials, reactives and inerts.
  • Effects of Pressure, Sulfur and Oxygen on the Rate of Decarburization from Liquid Steel

    pp. 195-201

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    The study was made on the rate of decarburization of molten steel in the low carbon content range ([%C] ≤0.1 mass%) under reduced pressure to reveal the effects of sulfur content of molten steel, pressure and CO bubble formation in the metal bath. The chemical reaction rate constant at gas-metal interface was estimated. The value obtained was far greater than that of previously reported value by Harashima et al.using CO2-CO-Ar gas. The reaction model analysis was made on the assumption that agitation by the formation of CO bubbles increased the interfacial area of bath surface.
    Three-step, i.e. mass transfer in metal and gas phases and chemical reaction at gas-metal interface were taken into consideration in the model.
  • Development of a New Technology for Controlling NOx Gas Generation on Pickling of Stainless Steel and Titanium Metal by Nitric-hydrofluoric Acid

    pp. 202-209

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    In order to control NOx gas emissions on pickling both stainless steel and titanium metal with nitric-hydrofluoric acid, a new control system has been investigated in laboratory and tested at a pickling plant, which doses hydrogen peroxide into the pickling bath automatically. The system includes pairs of platinum electrodes and electrolyzers, pumps for injecting hydrogen peroxide solution into the pickling bath, and their controllers. Results of the tests at the pickling plant showed that the NOx gas concentration can be lowered to 50200 ppm and consumption of the nitric acid was reduced apparently by dosing hydrogen peroxide so as to oxidize most of nitrous acid on pickling stainless steel, or as to oxidize whole nitrous acid and go to slight excess on pickling titanium metal. It was also verified that the electrolytic current measured in the pickling bath was of use as index which showed the concentration of remaining nitrous acid or hydrogen peroxide excessively added. The amounts of consumed hydrogen peroxide through pickling using this system was about 0.92 or 0.82 mole for one mole of SUS304 or titanium metal, respectively.
  • In situ Measurement of Dissolved Ion Concentration inside an Artificial Crevice by X-ray Fluorescence Micro-probe Technique

    pp. 210-213

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    In this study, solution chemistries inside artificial crevices of high purity nickel and Type 316 stainless steel were investigated by in situ energy dispersion X-ray fluorescence microanalysis technique.
    Concentration of dissolved metal ions inside the artificial crevice was successfully measured by the technique.
    In case of high purity nickel, diffusion coefficient of nickel ions inside the artificial crevice was estimated as approximately 6×10-6cm2/s.Super-saturation of nickel ion at steel/solution interface inside the artificial crevice prior to formation of salt films on the metal surface was detected.The concentration was about 1.4 times higher than the saturated value.
    In case of Type316 stainless steel, concentration of iron, chromium and nickel ions inside the artificial crevice were decreased similarly when the potential was stepped down to open circuit potential from 0.6 V (vs. SCE). The diffusion coefficient of these ions was estimated as 8.4×10-6cm2/s.
    This technique is very useful for analyzing local solution chemistries.
  • Coherent Laves Phase Finely Precipitated in Heat Resisting High-W and 10% Cr Ferritic Steels

    pp. 214-221

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    In recent advanced high Cr ferritic steels, it is known that the Laves phase precipitates during creep test when the steels contain a relatively high level of Mo+W content. The Laves phase is believed to be granular in shape and to exist in the boundaries of lath, block, packet and prior austenite grains, but a number of fine Laves-phase precipitates are found to exist even inside the martensite lath in the tempered steels containing 10 mass% Cr and 4.6 mass% W. The shape of this Laves phase is plate-like, and the size is below 300 nm. The crystallographic relationship between the fine Laves phase and the matrix phase is as follows; (111)ferrite//(001)Laves and [011]ferrite//[110]Laves. In the microstructure aged at 923 K for 714 Ms, the fine precipitates of the Laves phase disappear inside the martensite lath, and coagulated Laves phase is observed at the lath-, block-, or packet- boundaries. Only the low C steel containing 0.08% C and 3% W shows a few amounts of the fine precipitates of the Laves phase after aging at 923 K for 7.268 Ms. This compositional dependence of the precipitation behaviour can be understood qualitatively with the aid of the System-Free-Energy Concept.
  • Magnetic Properties of Fe-Cr-C and Fe-Cr-C-Ni Alloys

    pp. 222-228

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    Structures and magnetic properties of Fe-17.5mass%Cr-0.5mass%C and Fe-17.5mass%Cr-0.5mass%C-zmass%Ni(z=l-2.4) alloys were studied. The Fe-17.5mass%Cr-0.5mass%C alloy consisted of ferromagnetic α and M23C6 phases when annealed at temperatures below the A3 temperature, and showed good soft magnetic properties with a high relative permeability. On the other hand, the solution treatment of the alloy resulted in the formation of paramagnetic γ phase with a low relative permeability. However, the relative permeability of the alloy increased as the temperature decreased. This was due to the transformation from the γ phase to the ferromagnetic α' phase. The addition of Ni to the Fe-17.5mass%Cr-0.5mass%C alloy lowered the transformation temperature, Ms, and stabilized the paramagnetic γ phase. The annealing of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys also resulted in theformation of ferromagnetic α and M23C6 phases, and showed soft magnetic properties. However, the soft magnetic properties of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were slightly inferior to those of the Fe-17.5mass%Cr-0.5mass%C alloy, mainly due to the smaller grain size of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys. It was found that the soft magnetic properties of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were significantly dependent on the residual stress. The soft magnetic properties of the optimally annealed Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were superior to those of the commercial Fe-18mass%Cr-8mass%Ni alloy.

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