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

Tetsu-to-Hagané Vol. 98 (2012), No. 3

  • Effect of Changes in Sulfur and Oxygen Concentration on Change in Nitrogen Concentration in Liquid Steel during CaO-CaF2-Al2O3 Powder Blowing under Reduced Pressure

    pp. 75-83

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    DOI:10.2355/tetsutohagane.98.75

    To examine the change of the rate of nitrogen desorption with sulfur concentration and low oxygen concentration change, the rates of nitrogen desorption from molten steel were measured with 60mass%CaO-40mass%CaF2 flux powder or 35mass%CaO-50mass%CaF2-15mass%Al2O3 flux powder blowing onto 1500kg heats of molten steel through a top lance under the reduced pressure by using the high frequency induction furnace. Temperature of molten steel (<0.001%C, 0.5%Mn, 0.2%Si, 0.04-1.0%Al, 0.0011-0.0071%S) was held at 1873K.
    Whereas concentrations of sulfur and nitrogen were decreased by the flux powder blowing, concentration of calcium was increased. The apparent rate constant of desulfurization was increased with increasing aluminum concentration regardless of flux composition. However the rate constant of nitrogen desorption was depended on activity of surface activity elements and flux composition. It was estimated that the increase of rate constant was caused by decrease of oxygen activity in molten steel that was determined by reaction between Al2O3 in flux and aluminum in molten steel.
  • Estimation of Number Density of Particles Considering Their Morphology and Size-distribution in Particle Dispersion Strengthening Steels

    pp. 84-88

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    DOI:10.2355/tetsutohagane.98.84

    The number density of particles was estimated regarding to the high strength steels containing non-spherical shaped precipitates with various size. The shapes of particles were evaluated by modeling based on the experimental results obtained by transmission electron microscopy. When the spatial degrees of freedom of particle size were restricted to two-dimensions, the effect of particle size distribution on the number density became relatively small compared to the case of the three spatial degrees of freedom. This finding suggested that the number density might be obtained from the mean particle size. It was noted that the effect of size deviation could be negligible when the particles were platelet-shaped and their thickness was assumed to be constant.
  • Experimental Analysis of Thickness Reduction Limits in Ultra Thin Stainless Steel Foil Rolling

    pp. 89-95

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    DOI:10.2355/tetsutohagane.98.89

    In rolling of ultra thin stainless steel foil, there are two rolling limits. One is owing to elastic deformation of work rolls, and the other is owing to edge crack of rolled foil. In this paper, fundamental investigation was conducted about the basic characteristic of the rolling limits of ultra thin stainless steel foil. The influence of several rolling conditions on minimum thickness and behavior of edge crack were investigated experimentally. This paper provides new formula to predict the minimum thickness in ultra thin foil rolling. The relation between the edge crack depth and the rolling conditions is also discussed. The edge crack expands with rolling passes. However, the degree of the edge crack at same foil thickness shows different behavior depending on rolling conditions. The depth of edge crack rolled by small diameter work rolls is shallower than that of same thickness foil rolled by large diameter work rolls. Moreover, when Young's modulus of work rolls is high, it turns out that the edge crack is small. Based on detailed observation of the foil edge phenomenon, good correlation between edge crack depth and foil thickness at extreme edge portion is found. From those experimental results, it is suggested that the rolling conditions advantageous to control edge drop are effective to suppress edge crack expansion.
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  • Effects of Notch, Carbon Content and Boron Addition on Torsional Fatigue Property of Induction Hardened Middle Carbon Steels

    pp. 96-103

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    DOI:10.2355/tetsutohagane.98.96

    The purpose of this study is to clarify effects of notch, carbon content and boron addition on torsional fatigue property of induction hardened middle carbon steels. The torsional fatigue strength of smooth specimen increased with increasing carbon content. On the other hand, there is no effect of carbon content for notched specimen. In the torsional fatigue test of notched specimen of steel with high carbon content, a static final fracture is caused immediately in mode I associated with intergranular fracture after the crack occurs from the notch. This is because fatigue fracture toughness of higher carbon steel is not so high. The torsional fatigue strength of notched specimen of higher carbon steel is increased by the addition of boron. The fraction of intergranular fracture in the crack growth region of mode I fracture is decreased by the addition of boron. This is caused by the increase in grain boundary strength due to the addition of boron. Improvement of torsional fatigue strength of notched specimen of higher carbon steel by the addition of boron is attributed to the delayed static final fracture in the process of fatigue crack growth due to the improvement of fatigue fracture toughness caused by the increase in grain boundary strength.
  • Development of Fe Base Phase Change Materials for High Temperature Using Solid-Solid Transformation

    pp. 104-108

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    DOI:10.2355/tetsutohagane.98.104

    Fe base Phase Change Materials (PCM) for high temperature around 953-1273K using multiple solid-solid transformations were developed. The amount of latent heat of PCM samples were measured by Differential Scanning Calorimetry. The amount of latent heat of Fe-xCo samples increased with increasing Co addition. The reducing atmosphere was suitable for the samples developed in this work. The durability performance of samples was confirmed by heat treatment experiments. From the viewpoint of heat accumulation/supply ability, cost and durability performance, Fe-Co(-Cr) system alloy is one of the most suitable Phase Change Materials for heat recovery from high temperature exhaust gases.

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