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

Tetsu-to-Hagané Vol. 83 (1997), No. 12

  • Assessment of Al Deoxidation Equilibrium in Liquid Iron

    pp. 773-778

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    Previous literature thermodynamic values for strong deoxidizer such as aluminium are not in good agreement with the observed results and measurements. This discrepancy between predicted and measured results is due to an incomplete expression of the activities of dissolved oxygen and deoxidizer in current literature. Namely, only first order interaction parameters are available despite the very strong interactions among the dissolved elements.
    In the present work, the aluminium-oxygen equilibrium in liquid iron reported by other investigators was assessed to develop values for the first and second order interaction parameters.
  • Desiliconization, Desulfurization and [Mn] Increase of Hot Metal with CaO-MnO-CaF2 Flux

    pp. 779-784

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    Experiments were conducted on the hot metal treatment by adding CaO-MnO-CaF2 flux to 2kg carbon-saturated iron at 1350°C.
    (1) By adding CaO-MnO-CaF2 flux, desiliconization, desulfurization and [Mn] increase of carbon-saturated iron occurred simultaneously.
    (2) From the equilibrium oxygen partial pressure determined by [Si]-(SiO2) and that by [Mn] (MnO), the reaction: [Si]+2 (MnO)=2[Mn]+(SiO2) is considered to have almost reached equilibrium state.
    (3) By comparing Ls (=(%S)/[%S]) observed and that calculated using the numerical values of the sulfide capacity of CaO-SiO2-CaF2 slag and the equilibrium oxygen partial pressure, desulfurization is also considered to be in equilibrium state.
  • Effect of Electrolysis Conditions on the Morphology and Crystal Orientation of Zinc Electrodeposit

    pp. 785-790

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    The effect of electrolysis condition on the morphology and crystal orientation of zinc electrodeposit was investigated by using the polycrystal commercial low carbon Al-killed steel sheet as a base material and the sulfate bath under the current density of 50-200A/dm2, flow rate of 1-2m/s and bath temperature of 50-70°C. Under the conditions where overvoltage of electrodeposit is high, such as high current density, low flow rate and low temperature, heteroepitaxy of steel/zinc decreases, so that zinc crystals become fine and random in size and growth direction. Under the high overvoltage conditions, orientation indexes of (0002) Zn and (1013) Zn decrease but those of (1011) Zn and (1010) Zn increase. When zinc electrodeposits grow heteroepitaxially, (0002) Zn and (1013) Zn planes are preferred.
    From these results, zinc electrodeposits are thought to progress as follows:
    At initial stage of plating, zinc electrodeposits grow heteroepitaxially at preferred orientations of (0002) Zn and (1013) Zn. Then, random growth of zinc begins partly on the (0002) Zn and (1013) Zn and finally random growth of (1011) Zn and (1010) Zn occurs partly on the (0002) Zn and (1013) Zn.
  • Structure and Performance of Polyester Films Having High Melamine Concentration in the Surface

    pp. 791-796

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    Structures of polyester films having high melamine-formaldehyde resin (MF) concentration in the surface were investegated by X-ray photoelectron spectroscopy, Fourier transformation infrared spectroscopy, and high frequency grow discharge spectroscopy. In films in which methylated MF enriched in the surface, MF concentration had a gradient from the surface to the interface with primer film. This structure of the film gave excellent stain resistance and excellent formability because of high MF concentration in the surface and low MF concentration in the bulk of the film. A mechanism proposed in the previous paper seemed correct from the film structure. In films in which butylated MF enriched in the surface, MF concentration was very high only in the surface of the film and constant in the bulk. This structure gave excellent stain resistance because of high surface MF concentration, but not so good formability. Butylated MF seemed to be enriched in the surface of the film because of low surface tension compared with that of polyester resin or solvents in paints. In combination of methylated MF and non-neutralized catalyst, the film had uniform MF concentration through the depth. This film didn't show good formability and stain resistance because of both low surface concentration of MF resin and uniform concentration of MF resin in the bulk.
  • Control of Oxide Particle Size and Recrystallized Grain Structure in Oxide Dispersion Strengthened Ferritic Steel

    pp. 797-802

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    The size change of oxide particles in oxide dispersion strengthened (ODS) ferritic steels was quantitatively evaluated by X-ray diffraction and TEM. Althougth yttria (Y2O3) particles are thermodynamically stable and do not have any solubility limit in 13% Cr steel, after 48h mechanical alloying (MA) by high energy ball mill, peaks of Y2O3 or any other peaks of precipitates were not observed. The size change of oxide particles was detected by small angle X-ray scattering. Oxide particles became smaller with MA time. Small addition of titanium was very effective on refining of solid solutioning of oxide particles. By heating of as-MA powders above 1273K, precipitation of new oxide particles which were identified with yttrium and titanium bi-oxide. Recovery and recrystallization properties of ODS ferritic steels were influenced by Y2O3 and titanium content. Extrusion at low temperature was effective to make the grain with low dislocation density and low aspect ratio.
  • Role of Microstructures on Fracture Toughness of Heat Affected Zone of Ti-killed Steel

    pp. 803-808

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    Role of microstructures on the improved fracture toughness has been analyzed for the heat affected zone of weldment in Ti-killed steel. A microstructural features of Ti-killed steel is decrease of coarse bainitic ferrite, αB°, and increase of the mixed area of αB°and quasipolygonal ferrite, αq, besides the presence of intragranular ferrite. The brittle fracture initiation is not from large particles or inclusions, but at the intersections of small αB° grains with different orientations in a mixed area of αB° and αq in the proximity of boundary between coarse αB°. Ductile crack growth resistance represented by the slop of R-curve is also higher in Ti-killed steel compared with Al-killed steel. Together with observation of deformed microstructures, it is discussed that the decrease of coarse αB° grains in Ti-killed steel suppresses brittle fracture initiation by reducing plastic constraint and the increase in the mixed area of αB° and αq enhances ductile crack growth resistance by accommodating large strain.
  • Effects of Oxygen Content of Molten Steel on the Machinability of Low-carbon S-Pb Free-machining Steel Cast by Continuous Casting

    pp. 809-814

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    A study was made to clarify the effects of oxygen content of molten steel on the machinability of low-carbon S-Pb free-machining steel cast by continuous casting.
    The machinability of this steel was deteriorated by increase of the oxygen content of molten steel and oxygen potential of slag: (%T.Fe)+(%MnO) after LF treatment. It was estimated that the cause of the deterioration of machinability was the increase of amount of MnO rich, MnO·SiO2system large oxides, which promoted the abrasive wear of tool because of their hardness and the size of oxides also promoted the wear. And it was supposed that the large oxides were formed by the contamination of Si and SiO2from added alloy and firebrick, and reoxidation by the involved high oxygen potential slag on Pb-injection, and the oxides trapped by solidified shell on the continuous casting, give the effects on the machinability. From the results of previous and this study, it seemed that the proper control of the oxygen content of molten steel considering the effect of oxygen content on the machinability through the size, shape and formability of MnS and the amount of MnO·SiO2system large oxides, was very important to improve the machinability on the production of this steel by continuous casting process.
  • Influence of Carbon Content on Superplastic Behaviour in Ti and B Doped Cr-Mo Steels

    pp. 815-820

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    Superplasticity has been investigated in various ferrous alloys and steels. However, in these materials, especially in the hypoeutectoid steel bellow A1 temperature, the relationship between the content of carbon and elongation to failure is not obvious. In the present investigation, the influence of carbon content on superplastic behaviour is studied using carbon steels based on Cr-Mo steel. In order to obtain the fine grain structure, a small amount of Ti and B were added and the content of carbon was controlled to be in the range of 0.24% to 0.83%. The largest value of elongation to failure was 644% which was obtained by the tensile test of the specimen containing 0.58% carbon. The temperature and strain rate at which the maximum value was obtained were 710°C and 5×10-4s-1 respectively. Of all the specimens, this specimen had the minimum grain size. Moreover, the area fraction of carbide took the maximum value at the temperature where the largest elongation value was obtained. These results show that the addition of carbon has an effect on grain refinement by formation of carbide, but excess amounts of carbons (>0.6%) bring about premature failure because of coarse microstructure and larger carbide.
  • Synthesis and Property Evaluation of P/M Ti-6Al-2Sn-4Zr-2Mo/TiB Particulate Composites

    pp. 821-826

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    Conventional titanium alloys such as Ti-6Al-4V show lower stiffness, poorer abration-related properties and poorer high temperature properties than nickel-based alloys. In order to overcome these drawbacks, an attempt was made to produce titanium-based particulate composites using the blended elemental powder metallurgy method. Firstly, the effect of titanium powder size on the sintered density and how to disperse the reinforcing ceramic particulates uniformly in the matrix were investigated in detail to optimize processing conditions. It was shown that the size of titanium powder needs to be smaller than 45μm (-325mesh) to raise the sintered density to a critical value of 95%. The uniform distribution of the particulates was accomplished by a forced mixing technique with a mechanofusion apparatus. Secondly, Ti-6Al-2Sn-4Zr-2Mo/TiB composites were produced using the above processing conditions. The composites showed superior tensile properties, Young's modulus and high cycle fatigue strength compared with those for the matrix alloy. For example, high cycle fatigue strength at 107 cycles was increased to 490MPa from 333MPa for the matrix alloy by the dispersion of 10% TiB. The tensile and Young's modulus data were compared with those predicted by the existing models, and three main factors such as the increase in tensile strength, increase in Young's modulus and matrix microstructure refinement were found to contribute to the increase in high cycle fatigue strength.
  • Upper and Lower Bounds in Flow Stress of a Dual Phase Steel Predicted by the Secant Method and Related Microstructures

    pp. 827-832

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    Elasto-plastic flow curves of dual phase steels consisting of martensite and ferrite have been predicted by using the secant method proposed by WENG. The predicted flow stress for a given volume fraction of martensite becomes the upper bound when the matrix is considered to be martensite, whilst the predicted flow stress becomes the lower bound when the matrix is ferrite. This prediction is compared with experimental results obtained from Mn-Si-C martensite-ferrite steels where the volume fraction and morphology were altered by changing heat treatment. It is found that the prediction is in good agreement with the experimental results when the matrix structure can be identified by means of optical microscopy. In the case where the matrix structure is percolated and is not distinguishable, the flow stress curves lie between those two bounds.
  • Behavior of Oxide Precipitation during Rapid Solidification of Steel

    pp. 833-837

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    The behavior of oxide precipitation during rapid solidification of steel was investigated using Ti deoxidized steel. The number, size and composition of oxides in rapidly cooled steel have been observed and theoretically analyzed to compare with those in slowly cooled steel and continuously cast slab. The results obtained are as follows.
    In rapidly cooled steel, whose cooling rate is more than ten times as large as continuously cast slab, many fine oxides smaller than 1μm are observed. The composition of the oxides mainly consists of Ti2O3, Al2O3 and MnO. The Ti2O3 content in the oxide smaller than 1μm is relatively high. By comparing the Ti2O3 content in the oxides larger than 1μm between rapidly and slowly cooled steels, it has been found that Ti2O3 content is lower in the rapid cooling than the slow cooling. As a result of the theoretical analysis of the oxide behavior during solidification, it has been found that the many fine oxides smaller than 1μm precipitate and grow during solidification of steel.
  • Spatial Distribution of Metallic Vapor in Ar Thermal Plasma on Melting of Fe and Fe-Mn Alloy

    pp. 838-843

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    Metallic vapor pressure distribution in Ar thermal plasma on melting of metal was determined by using the values of total absorption ratio of spectra (β) which were calculated from Ar density and Ar spectral intensity. There is good agreement between the vaporization rate obtained from the distribution of metallic vapor pressure by using Hertz-Knudsen equation and that of measured.
    The metallic vapor pressure decreased from molten surface to bulk of Ar plasma. Due to the enhanced vaporization mechanism, the maximum metallic vapor pressure was not at the anode spot, but at outer region of anode spot which has the highest temperature at the molten surface.
  • Evaluation of the Managerial Environment for Japanese Steel Industry in East Asian Countries with AHP Method

    pp. 844-849

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    Recently, East Asian countries have been paid much attention to, because of their high economic growth rate, and many Japanese companies such as cars, electric and electronic industries are expanding production in these countries. To correspond to such a trend of these steel customers, Japanese steel companies have gradually increased their production overseas. In this research therefore, we have evaluated the managerial environment in those East Asian countries by means of the Analytical Hierarchy Process, using basic data obtained from both existing statistics and questionnaire. In questionnaire particularly, it became clear that steel industries attach much importance not only to their demand, but also to their social and political situation. Speaking the results of managerial environment evaluation for the steel industry for example, Thailand is the highest, but China which is considered to have a large market potentiality, has been evaluated rather lower, probably because of some apprehension on her social and political situation in the future.
  • Analysis of Tramp Element in Iron Scraps

    pp. 850-855

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    Recycle of materials is expected to reduce environmental burden which accompanies the production of materials. However, the recycle may also result in concentration of tramp elements in the materials. In order to promote the recycle of materials, we have to have clear prospect for the accumulation of the tramp elements. In this study, we have collected iron scraps from various scrap yards in Japan and analyzed the concentration of such tramp elements as copper, tin and chromium. We also estimated tramp element accumulation at shredding processes. The result shows that, although Cu and Sn concentrations in the iron scraps are close to their critical levels, the tramp element accumulation at shredding processes is currently relatively small.

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