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

Tetsu-to-Hagané Vol. 95 (2009), No. 9

  • Effects of Ti Addition on As-cast γ Grain Structure in Hyper-peritectic Carbon Steel

    pp. 629-635

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    DOI:10.2355/tetsutohagane.95.629

    Effects of titanium addition on as-cast austenite grain size in 0.2 mass% carbon steel cooled at 0.03°C/s has been studied. The average austenite grain size was reduced from 4.3 to 1.9 mm by increasing the titanium concentration from 0 to 0.13 mass%. Two different shapes of Ti(C, N) particles were observed in the solidified samples; one was a facet shape which were dispersed over the whole observation area and the other was a filmy shape, most of which were located on the austenite grain boundary. Thermodynamic calculations and EPMA analyses showed that the facet shaped Ti(C, N) particles crystallize at relatively high temperatures, while the filmy shaped ones form from the last solidifying liquid in the inter-dendritic regions at lower temperatures. The latter Ti(C, N) is considered to provide the grain refinement effect of austenite grain structure. The grain refinement effects of titanium are further discussed by comparing the results of 0.2 mass% carbon steel with those of 0.45 mass % one, which supports the substantial effect of the filmy shaped Ti(C, N) on the as-cast austenite grain structure.
  • Model Based State Feedback over Networks with Communication Delays

    pp. 636-639

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    DOI:10.2355/tetsutohagane.95.636

    A model based networked control system is investigated in this paper, which is useful for realizing plant-level networked control of iron and steel processes. Sampled data of the state of a plant are transfered to a controller over a network with a communication delay. Then, a model based state feedback is introduced, which uses the model state instead of the plant state. An update rule is presented for resetting the model state appropriately based on the sampled data of the plant state. A necessary and sufficient condition of stability of the system is also derived as an eigenvalue test of a matrix.
  • Determination of the Mass per Unit Area of Galvanized Steel Sheet by Anodic Stripping Voltammetry

    pp. 640-644

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    DOI:10.2355/tetsutohagane.95.640

    A simple and sensitive method is described for the determination of the mass per unit area of galvanized coatings by differential pulse anodic stripping voltammetry in the presence of iron matrix. The optimized experimental conditions were as follows: Zn2+ in a sample solution (5 mL) containing a 0.07 M nitric acid–0.05 M sulfuric acid mixture at pH 4 was electrodeposited as zinc amalgam in a hanging mercury drop electrode at −1.15 V vs. Ag/AgCl for 2000 s with stirring; the deposits were then anodically stripped in the potential range −1.15 to −0.7 V vs. Ag/AgCl at a scan rate of 30 mV s−1. The interference of the Fe3+ matrix was eliminated by reducing it to Fe2+ with L(+)-ascorbic acid, and the maximum permissible concentration of Fe2+ was up to 1.5 mg mL−1 by the addition of 0.1 M L(+)-ascorbic acid. The calibration (peak height vs. Zn2+ concentration) graph is linear in the concentration range 20 to 2000 ng mL−1 with relative standard deviation of 2.7% for 100 ng mL−1 (n=5). The possible interferences have been evaluated. The proposed method was applied to the determination of the mass per unit area of galvanized coatings with good precision and accuracy.
  • Structural Defects Formed in Alloy Layers of Fe–Al System by Diffusion in Air

    pp. 645-648

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    DOI:10.2355/tetsutohagane.95.645

    The aluminizing process is performed in air at 1173K after the aluminum has been bonded to a carbon steel S45C surface by hot dipping or pressure bonding, Al-rich alloy layers are first formed by diffusion of Al into the steel, but as the diffusion progresses, these layers become Fe-rich. However, each of the alloy layers is found to contain structural defects. In this work, the nature of these defects has been studied by EPMA and XRD analysis. It was found that void-like defects formed during the early stages of diffusion were mainly a combination of Al2O3 with voids and Al2O3, and that the band-like defects formed at later stages in the boundary region between FeAl and αFe were mainly composed of Al2O3. These Al2O3 formations are most likely the result of oxygen penetrating into Kirkendall voids and subsequently reacting with Al.
  • Corrosion Characteristics of Inter-metallic Compounds FeAl and FeAl(Cr) in HCl, NaOH, and NaCl Solution

    pp. 649-654

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    DOI:10.2355/tetsutohagane.95.649

    To obtain information about the corrosion characteristics of aluminum treated in a pressurized vessel. Corrosion tests on inter-metallic compounds FeAl and FeAl(Cr) in 1 mole solution of HCl, NaOH, and NaCl were performed. As a result, the mass decreasing curves of FeAl and FeAl(Cr) in HCl solution were at first greatly increasing to approximately 90 kg/m2 per year until hitting 250 ks, and then decreasing to one-fiftieth at 2200 ks. The mass decreasing curves of SUS316 steel and CrMo steel in HCl solution were continuously changed, compared to the inter-metallic compounds. It is clear that the mass decreasing rate of FeAl(Cr) at 2200 ks was nearly equal to that of SUS316 steel, which the rate became larger in order for SUS316 steel≒FeAl(Cr), FeAl, CrMo steel. The cause of the decreasing corrosion rate at 2200 ks seems to be because of the formation of AlO(OH) or CrO(OH). The mass decreasing rate in NaCl solution became larger, in the order of SUS316 steel, FeAl(Cr), FeAl, and CrMo steel. However, corrosion in NaOH solution for all the materials was hardly observed.
  • High-temperature Fatigue Property of a W–Mo Type High-speed Steel

    pp. 655-659

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    DOI:10.2355/tetsutohagane.95.655

    Fatigue tests of W–Mo type high-speed steel specimens were carried out at 20 and 600°C under various stress amplitudes σ. Fatigue lives of the specimens tested at 20 and 600°C under each amplitude between 1100 and 1400 MPa were identical, but under each amplitude between 700 and 1000 MPa, those of the specimens tested at 600°C were shorter than those at 20°C. Fracture origins of the specimens fatigued at 20°C under all stress amplitudes and at 600°C under σ≧1100 MPa were large aggregates of 10~13 μm, comprising two or three M6C·MC carbides, and those tested at 600°C under σ≦1000 MPa were large isolated M6C·MC carbides of about 8 μm. When fatigued at 20°C under all stress amplitudes and at 600°C under σ≧1100 MPa, a crack propagated between two voids, produced by decohesion of the M6C/MC interfaces, in adjacent large two M6C·MC carbides which constitute a carbide aggregate, whereas in the specimens tested at 600°C under σ≦1000 MPa, cracking was initiated from the voids in large isolated M6C·MC carbides of about 8 μm. The fatigue lives of the specimens tested at 600°C under σ≦1000 MPa are shorter because the nucleation of cracks from isolated M6C·MC carbides occurs more rapidly than that of cracks in large M6C·MC carbide aggregates.
  • Measurement of Carbon Content in Steel by LIBS Which Transmits a Laser Beam in Optical Fiber

    pp. 660-664

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    DOI:10.2355/tetsutohagane.95.660

    Utilizing new laser transmission technology, we have developed a laser induced breakdown spectrometer (LIBS) that allows to obtain uniform energy profile by transmitting high-energy laser emitted from GP-YAG through optical fiber, implemented measurement of carbon content in steel and demonstrated its capability of accurate and fast measurement. The spectrometer made it possible to measure both carbon content distribution in the depth direction and average carbon content in steel at the same time by setting the diameter of the laser light with energy of 90 mJ to 0.9 mm on samples after transmitting it by the optical fiber. In addition, we were able to find carbon content in steel in a coefficient of correlation over 0.99 by using 50 shots average data after 3.6 μm from surface.

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