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

Tetsu-to-Hagané Vol. 84 (1998), No. 11

  • Tensile Strength of Carbon Steel during and after Solidification

    pp. 763-769

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    Phase dependence of tensile strength of carbon steel during and after solidification has been studied by a technique for high temperature tensile test The experimental thechnique enabled a sample to melt and solidify without crucible, and measured a minute load in a solidificatlon temperature range.
    A numerical model for the analysis of phase transformation during and after solidification was developed with an assumption of local equilibrium at interfaces.
    The tensile strength of carbon steel was dependent on the phase state but not composition. Predicted equations of tensile strength of δ phase and γ phase were estimated from experimental results.
    σδ=0.011(Tδ, start-T)+1.1, MPa
    σγ=0.067(Tγ, start-T)+65, MPa
    0, 0005 mass%≤C≤0.55 mass%, 1550K≤Temp.≤1800K.
    Tensile strength of δ phase state is smaller than that of γ phase, and temperature dependence of tensile strength of δ phase is also smaller than that of γ phase
  • The Deviation from Matthiessen's Rule during Quench-aging of Si Added Low Carbon Steels

    pp. 770-776

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    The interaction between silicon and carbon atoms is discussed in Fe-C Si-steels which have been quenched from 823-973K to 273K and then aged at 523K.The changes in electrical resistivity and its deviation from Matthiessen's rule (DMR) during aging were examined for 0.04mass% carbon steels containing from 0.01 to 0.56 mass% silicon. The DMR was obtained from the difference between the electrical resistivity measured at 77K and 273K. The electrical resistivity during aging decreases for all steels which have been quenched from the ferrite phase region. The DMR increases for steels except the 0.01mass% silicon steel. The more the silicon content, the more the increments in DMR. These results can be explained from the assumption that the Si-C pairs formed in the as-quenched ferrite matrix would be decomposed with the precipitation of carbide during aging, corresponding to Mn-C(N) dipoles in Fe-Mn-C(N)alloys. The amount of solute carbon atoms, which was occurred by the decomposition of Si-C pairs and then contributed to the precipitation of carbide, increases with the increase of silicon content. The Si-C pairs may be formed in a short time during quenching by elastic interaction between silicon and carbon atoms, whereas the Mn-C(N)dipoles were combined at high temperature during solid solution treatment by chemical interaction between manganese and carbon atoms.
  • Corrosion Behavior of Organic Composite Coated Steel Sheet during Cyclic Corrosion Test

    pp. 777-784

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    Organic composite coated steel sheets show their excellent corrosion resistance during cyclic corrosion tests (CCT). To clarify corrosion behavior of these sheets, changes in corrosion products and elements of plating, chromate and organic resin layers during CCT were examined. Formation of crystalline ZnCl2·4Zn(OH)2 and superficial amorphous zinc carbonate were detected by X-ray diffraction, fourier transform infrared spectroscopy and Raman spectroscopy. And besides it was found by electron probe micro analysis, chemical analysis and fourier transform infrared spectroscopy that the corrosion products formed on organic resin layer contained silicon as zinc silicate from silica in organic resin layer.Consequently, weight of zinc in plating layer and silica in organic resin layer decreased, while that of nickel in plating layer, chromium in chromate layer and carbon in organic resin layer remained constant, and the corrosion products formed on organic resin layer contained zinc and silicon dissolved from each layer during CCT.
  • Effects of Cathodizing on the Durability of an IrO2-based Anode in an Electrogalvanizing Line

    pp. 785-789

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    The effects of cathodizing on the durability of an IrO2-based anode in an electrogalvanizing line (EGL) have been investigated. A comparison of the surface morphology of the anodes after electrolysis with anodic, cathodic, and periodically reversed currents indicated that the partial anomalous deterioration of the anode outside the strip width in EGL was caused by periodic cathodizing of the anode. The lifetime of the anode during the periodically reversed electrolysis significantly depends on the cathodic current density, the frequency of the current reversal, and the ratio of the cathodic period to the anodic period, tc/ta. The lifetime is shortened with an increase in the cathodic current density, frequency, and tc/ta. The consumption rate of the catalytic layer of the anode during the periodically reversed electrolysis was compared to that during cathodic current electrolysis. The results indicated that the periodic current reversal induced a significant increase in the consumption rate even at the same cathodic current density. The difference in the deterioration modes of the catalytic layers during the cathodic and periodically reversed electrolysis is also discussed.
  • Isothermal Aging Behavior of β Ti-Fe Alloys

    pp. 790-796

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    The isothermal aging behavior of Ti-5, 8 and 10 mass%Fe alloys at 673K, 723K and 773K was investigated by resistivity and hardness measurements, X-ray diffractometry and transmission electron microscopy. The Time-Temperature-Transformation diagram of the alloys was determined. In Ti-5 mass%Fe and Ti-8 mass%Fe, the isothermal ω phase precipitated by aging at all of the aging temperatures. Because the isothermal ω phase did not precipitate by 773K aging in T-10mass%Fe, the upper temperature limit for precipitation of isothermal ω phase in Ti-10mass%Fe will situate between 723K and 773K. Incubation period prior to nucleation of a phase is shortened with elevating aging temperature. The influence of Fe content on the time for nucleation of α phase was not clear. Only at 723K, resistivity and hardness of all specimens show second abrupt decrease by more than 600ks aging, which suggests the precipitation of TiFe.
  • Effect of VN Precipitates on Formation of Grain Boundary and Intragranular Ferrite in a High N-V Bearing Steel

    pp. 797-803

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    The enhancement of ferrite nucleation owing to vanadium nitride (VN) precipitated in the austenite phase was studied for a 0.14%C-1.45%Mn-0.06%V-0.009%N steel and the isothermal ferrite transformation behavior associated with VN precipitation was also quantitatively discussed.
    Vanadium nitrides precipitate on the austenite grain boundary in preference to the grain interior and increase the density of grain boundary ferrites. On the other hand. VN precipitates in austenite grain interior are less effective to intragranular ferrite nucleation. The calculation based on the classical nucleation theory shows that the activation energy of VN precipitates for a critical ferrite nucleus formation is one-fifth lower than that in case of no precipitate. The ferrite nucleation potency of VN precipitates is kept high even in higher temperature range above 700°C.
  • Effect of Grain Size and Boron on Resistance to Secondary Working Embrittlement of High-purity Ferritic Stainless Cold-rolled Steel Sheet

    pp. 804-810

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    The effbct of gmin size and boron on the resistance to the secondary working embrittlement of high-purity ferritic stainless cold-rolled steel sheet is investigated and analyzed. The mechanism for improving the resistance to the secondary working embrittlement by adding boron to high-purity ferritic stainless steel sheet is studied from the standpoint of the behavior of the segregated boron. The results obtained are as follows.
    (1) The secondary working embrittlement in Ti stabilized low C, N ferritic stainless steel sheet occures by the interganular fracture.
    (2) Refining the grain size improves the resistance to the embrittlement, but it remarkably deteriorates the deep drawing property.
    (3) Adding boron improves the resistance to the embrittlemnt, with ensuring the deep drawing property.
    (4) The morphology of fracture in the secondary working embrittlement changes from the intergranular fracture to the cleavage fracture by adding boron.
    (5) It is considered that the improvement of the resistance to the working embrittlement is due to strengthening the grain boundary by the segregated boron to the grain boundary instead of carbon. This agrees with the results obtained in the interstitial-atom free steel sheets.
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    1. Effect of VN Precipitates on Formation of Grain Boundary and Intragranular Ferrite in a High N-V Bearing Steel Tetsu-to-Hagané Vol.84(1998), No.11
  • Observation of Microfracture Behaviour of the Beta Titanium Alloy

    pp. 811-816

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    The purpose of this paper is to investigate the microfracture behavior of beta titanium alloy which is important for its toughening. The initiation and propagation of microfracture were observed by optical microscope, scanning electron microscope and transmission electron microscope. The microfracture propagation were prompted by the microcracks and also the coalescence of microcracks of nanovoids in a ductile fashion. It was observed that microcracks of the beta titanium alloy were occurred by the links of nanocracks. By the observation of microfracture behavior, it could be concluded that the alpha phase played more important role for the microfracture initiation and that the nanocrack initiation were influenced by the crystallographic orientation of alpha phase.
  • Toughening of 18%Ni Maraging Steel by the Combined Addition of Nb and B

    pp. 817-822

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    Effects of Nb content and solution treatment temperature on the tensile strength and fracture toughness were examined in 18% Ni maraging steel containing 0.00120.0013% B. When Nb was added as a boride former element, the recovery process of reverse-transformed austenite was retarded. This retardation of recovery led to the suppression of recrystallization and further to the rising in recrystallization temperature of reverse-transformed austenite. The recrystallization temperature was raised with increasing the Nb contents. When the addition of Nb was more than 0.16mass%, however, the fracture toughness was reduced markedly. This decrease of fracture toughness was ascribed to the thermal embrittlement which was caused by growth of NbB2 type borides. In conclusion, when Nb was added by an amount of 0.05 to 0.07 mass%, both strengthening and toughening can be realized without any thermal embrittlement, by means of the solution treatment in a wide temperature range where the steels are in a state of unrecrystallized austenite.
  • Analysis on the Characteristics and Future Potential of Japanese Iron and Steel Industry in the Direct Investment of the Japanese to ASEAN Countries

    pp. 823-828

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    We investigated the direct investment behaviors of Japanese industries to Asian countries focusing on the manufacturing industries, especially on the iron and steel one to estimate their direct investment in the future. The principal conclusions can be summarized as follows:
    (1) The development of Japanese industries to Asian countries could be explained by two main factors, exchange rate and the GDP gap between Japan and those countries.
    (2) The correlation between the direct investment of electric appliances industry and transport machinery industry and yen/dollar exchange rate are recognized higher enough, but it was lower as for the metal industry, although it shows a tendency of rising after 1990 years.
    (3) The correlation between the direct investment and the GDP gap also showed the similar tendency as described in (2).
    (4) The direct investment in 2005 years of the Japanese steel industry is expected to expand by 4 times from that in 1994 years on the average.
  • Influence of Non-linearity of I/O Relation in Life Cycle Inventory Analysis

    pp. 829-836

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    Life cycle accessment (LCA) has been widely used to evaluate the environmental load associated with products, materials and services from cradle to grave. Most of the effort in LCA so far has been devoted to construct the inventory database because collecting the related data is tremendously time-consuming process. On the other hand, problems of LCA as a evaluation tool also has to be considered. Typical LCI methods, such as I/O analysis and process analysis, assume that the relationships between the input and output for each process are linear. In fact, most of the relationship between the input and output for processes do not satisfy the linearity and so the influence of the non-linearity on the result has to be investigated to evaluate more accurate environmental load. This paper formulates the nonlinear analysis in LCA to extend the normal linearity-based LCA. In the formulation, a method to express the nonlinearity in the general format is newly proposed. Next, a general system for the evaluation of environmental load is developed using this formulation. It is shown that object-oriented approach is effective for the development. Using the developed system, influence of non-linearity on environmental load and the derived problems will be investigated. Finally, an effective method to modify nonlinear data, which is supposed to become important in the future, will be proposed.

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