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

Tetsu-to-Hagané Vol. 86 (2000), No. 9

  • Reduction Rate Analysis of Dense Wustite in Consideration of CaO Enrichment at Reaction Interface

    pp. 571-577

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    Dense wustite plates containing CaO were reduced with CO-CO2-Ar gas mixtures at 1273K. Soon after start of the reduction, formation of metallic iron was observed and the reduction rate increased gradually with increasing in reduction time. Lattice parameter measurement of the samples reduced to predetermined state revealed that CaO concentration in the unreduced wustite increased with decreasing in the distance from the wustite/iron reaction interface. The reduction rate was examined with modified model of alloy solidification in consideration of the CaO enrichment at the reaction interface. The apparent reaction rate constant, kc, was correlated well to the CaO concentration at the reaction interface, CT, not to the initial concentration, C0. The kc increased remarkably with increasing in CT up to about 2 mass% and tended to become constant where CT become more than 2 mass%. In consideration of the variation of kc with CT, mass change of wustite sample with reaction time was estimated reasonably with the reaction model proposed by the authors previously.
  • Microstructural Analysis of Rust Layers on Weathering Steels Exposed at Rural and Coastal Areas

    pp. 578-583

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    Weathering steel has been widely used for the bridge materials because of its superior atmospheric corrosion resistance. It has been, however, pointed out that the amounts of corrosion are greater used in coastal area than rural area. In order to clarify the differences of corrosion resistance between rural and coastal area, rust layers were analyzed in details by combining with FIB (Focused Ion Beam) and electron microscope. Analytical results indicate as follows:
    Inner layer of the rust exposed in rural area consists of multiple layers and thickness of each layer is less than 2μm. These layers have different composition and degree of enrichment in alloying elements, especially chromium. Though these layers consist of mainly FeOOH fine particles, crystalline FeOOH layer exists between fine particle layers. Rust layer exposed in coastal area did not show such multiple-layer structure. The layer consists of crystalline β-FeOOH and FeOOH fine particles. The crystalline β-FeOOH is not a single crystal but is an aggregation of ordered fine rust particles. A size of the fine particles of rust exposed in coastal area is not much different from that exposed in rural area. Major differences existed are structure and packing state of fine rust particles.
  • Effect of Small Amount of Inorganic Additives on the Lightness and the Gloss of Electrogalvanized Steel Sheets

    pp. 584-590

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    Zn was electrodeposited on a commercial steel sheet from the sulfate baths containing a small amount of inorganic additives. The lightness and the gloss of deposited Zn were evaluated by the conventional techniques and the morphology was observed using an atomic force microscope. On the basis of their effect on the appearance of deposited Zn, the additives used were classified into following three groups: Fe, Ni, Co, Al, Mg and Mn (Group I), Cr, W, Mo and Zr (Group II) and Cu, Pb, Cd, In, Sn, Ge, Sb and Ag (Group III). The additives of group I hardly affected the morphology, crystal orientation and surface roughness of deposited Zn, and therefore they caused no change in the lightness and the gloss compared with the deposit from additive-free bath. Since the additives of group II enhanced the (0002) orientation index of deposited Zn, the surface roughness decreased significantly. As a result, the lightness and the gloss of deposited Zn increased although the morphology was scarcely affected by these additives. The additives of group III caused a significant change in the morphology of deposited Zn and therefore the surface roughness changed considerably depending on the additive concentration in the baths. With an increase in the additive concentration in the baths, the lightness and the gloss were generally decreased, although the addition of extremely small amount of Cd, Ge, Sb and Ag compounds to the baths increased the lightness and the gloss of deposited Zn.
  • Nucleation Kinetics in Materials with a Time-independent Driving Force during Phase Transformation

    pp. 591-594

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    The dynamics of clusters during phase transformation can be described by the Fokker-Planck equation. In this paper asympototic behaviours of the Fokker-Planck equation were investigated. The driving force for nucleation in an infinite system is time dependent and the nucleation rate approaches a constant value, steady state nucleation rate. However, if the drivig force is constant during the phase transformation, the number of clusters having the critical size increases with time. Therefore, the number of the stable clusters increases with time in the case that an external driving force is applied to compensate the decrease in the chemical driving force. This result may be helpful to develop a new method of thermomechanical control process.
  • Effects of Striker Shape and Attached Position of Strain Gage on Measured Load in Instrumented Charpy Impact Test

    pp. 595-601

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    Instrumented Charpy impact test is widely used for the evaluation of toughness of many kinds of materials such as steel, aluminum alloys, polymers and ceramics with small scale specimens. In the test, therefore, it is important to record an accurate impact load. Generally, one can obtain measured load in the instrumented Charpy impact test by multiplying the output signal from strain gage attached to the instrumented striker by load-calibration factor assuming a liner relationship between the strain gage signal and applied load. Although JIS or ISO describes about the instrumented striker, amplifier, data processing parameter and etc., detailed method on load measurement is hardly described in any standard.
    In the present study, two types of striker were used. The strain gages were attached to 4 positions in each striker. Instrumented Charpy impact test was carried out using these strikers in order to investigate the effect of gage position on actual impact load. By the finite element analysis, the effect of the strain gage position on the measured load was also investigated. As the result, it became clear that the accurate impact load was not measured around the end of slit which was introduced to release the constraining effect of deformation of the gage position from surrounding hammer; the effect of the vibration of the hammer appeared strongly around this position. However, it was possible to prevent the effect of such vibration by attaching the gage away from such position.
  • Tensile Properties and Cyto-toxicity of New Biomedical β-type Titanium Alloys

    pp. 602-609

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    Co-Cr alloy, SUS 316L stainless steel, pure Ti and Ti-6Al-4V ELI have been used as implant materials. Ti-6Al-4V ELI has been most widely used as an implant material to date because of its excellent combination of biocompatibility, corrosion resistance and mechanical properties. Since toxicity of V etc., and high moduli of elasticity have been pointed out, β-type biomedical titanium alloys are recently getting much attentions. New β-type biomedical titanium alloys composed of non-toxic elements such as Nb, Ta, Mo, Zr and Sn with lower moduli of elasticity and greater strength were, therefore, designed using alloy design method based on the d-electron theory in this study.
    Tensile test, measurement of modulus of elasticity and evaluation of biocompatibility were conducted in order to investigate the mechanical properties and biocompatibility of the designed alloy. Tensile strength and elongation of Ti-29Nb-13Ta-4.6Zr are, in particular, equivalent to those of conventional biomedical titanium alloy such as Ti-6Al-4V ELI, and modulus of elasticity of Ti-29Nb-13Ta-4.6Zr is lower than that of Ti-6Al-4V ELI. The moduli of elasticity of the designed alloys are equivalent or lower comparing with those of conventional biomedical titanium alloys such as Ti-6Al-4V ELI and Ti-13Nb-13Zr. The biocomparibility of Ti-29Nb-13Ta-4.6Zr is equivalent to pure-Ti, and biocompatibility of Ti-29Nb-13Ta-4.6Zr is much greater than that of Ti-6Al-4V.
    The new β-type titanium alloy, Ti-Nb-Ta-Zr, designed in this study is expected to have greater performance for implant materials.
  • Heat Treatment Processes and Mechanical Properties of New β-type Biomedical Ti-29Nb-13Ta-4.6Zr Alloy

    pp. 610-616

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    Practical size ingot of new β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr, which was composed of non-toxic elements of Nb, Ta and Zr, with lower modulus of elasticity, high strength and excellent biocompatibility was tried to be fabricated. Then the heat treatment processes of the alloy, which gave a good balance of strength, ductility and modulus of elasticity, were investigated in this study.
    Practical size ingot of Ti-29Nb-13Ta-4.6Zr with a weight of 17 kg has been successfully fabricated. The distribution of alloying elements was homogeneous through the ingot. The practical size ingot can be easily hot forged and cold rolled by a total reduction of 98%.
    Ti-29Nb-13Ta-4.6Zr which was aged after cold rolling indicates higher strength and lower elongation as compared with those of the alloy aged after solution treatment. In the aging temperature range between 598K and 648K, the alloy indicates relatively higher strength and lower elongation. The precipitation of ω phase increases tensile strength and decreases elongation in the alloy aged between 598K and 643K after solution treatment. In the aging temperature above 673K, the precipitation of α phase increases tensile strength and elongation in the alloy aged after solution treatment. New alloy has excellent strength ductility relationship when aging temperature was above 673K.
  • Effect of Solute Mo and W on Transient Creep Deformation of High-Cr Ferritic Steels

    pp. 617-624

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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 160 to 168 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 εmin for model steels alloyed with Mo and W was one order of magnitude lower than εmin in base steel. Also it is found that transient creep stage is controlled by glide using the stress-change technique under the present experimental condition. Furthermore, the changes of strengthening factor can be described as a function of the solute mole fraction, C, times the second power of the size-misfit parameter, ε2b. In the range of high W mole fraction, however, the changes of strengthening factor deviate from the linear relation line which represents C×ε2b. This is suggested that transient creep of these alloys with high W mole fraction is controlled by cluster hardening, in addition to solid solution hardening.
  • Design of Ultrasonic Field in Liquid Metal Processing

    pp. 625-632

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    Sound fields in liquids have been studied for effective utilization of ultrasonic energy in materials processing. Experimental conditions under which small particles could be concentrated by ultrasound were investigated using a cylindrical acrylic resin vessel filled with a 13 wt% aqueous sugar solution in which polystyrene particles of 0.24 mm diameter were initially dispersed uniformly. A distribution of acoustic pressure in the sound field was measured under the above one condition using a commercial ultrasonic meter (a calibrated hydrophone with a voltmeter). Another distribution of acoustic pressure in a copper vessel was also measured under the condition at the same driving frequency and liquid depth. It is clarified that the successful conditions for concentration of small particles are the resonant conditions of ultrasonic standing wave field and that the sound field is affected by vessel material used. A numerical scheme has been developed on the basis of the finite difference solution of the linear wave equation. The scheme allows us to design sound fields considering material and thickness of a vessel, depth and properties of a liquid, and a dimension and arrangement of a transducer at various driving frequencies. The calculated pressure distributions agreed well with the measured ones. These results may be useful to design ultrasonic fields in such materials processing as suppression of thermal convection, separation of inclusions and directional control of reinforcing fibers in composite.
  • Production Mechanisms of Bloom and Pig Iron by a Small “Tatara” Furnace

    pp. 633-640

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    The mechanisms of pig iron “Zuku” making and steel “Kera” making from iron sand and charcoal using small Tatara furnaces have been cleared. The “Zuku” making furnace has larger zone at high temperature than the “Kera” making furnace. For the “Zuku” making, iron sand falls down, stays longer in the high temperature zone and is reduced and carbonized in higher carbon steel than for the “Kera” making. The higher carbon steel becomes molten pig iron and the less carbon steel becomes bloom with 1.0 to 1.5 mass% C. From the results of small Tatara furnaces, the difference of reaction mechanisms of Tatara furnaces for “Kera” making and “Zuku” making in the Meiji period has been discussed.
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