발간논문

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Effects of CaSi wire feeding on the impact toughness and the castability of Al-killed steel have been studied in full-scale industrial trials. The steel samples taken from a 40ton VAD vessel were subjected to the tensile and the Charpy impact tests for determining mechanical properties. In addition, the tundish nozzles through which Al-killed and Al-killed and Ca-treated steels had been cast were Xray diffractometrically examined. Calcium treatment of Al-killed steel remarkably increases the impact toughness of steel, which is considered to be due to uniformly distributed globular and small inclusions. In the Ca-added steel, the conversion of alumina into molten calcium aluminate inclusions substantially improves the steel castability. Since the aluminum retention is extremely small, it deems necessary to determine if an improved aluminum deoxidation could be obtained with the A1 wire feeding practice.

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It was studied that the trace amounts of thorium in Na₂WO₄ solution was removed through the adsorption of thorium by ferric hydroxide. The adsorption of thorium in Na₂WO₄ solution took place above pH 10. When the concentration of Na₂WO₄ was higher than 0.050M, the adsorption of thorium was increased with increasing pH. The increase of Na₂WO₄ concentration caused the adsorption of thorium to decrease. The increase of temperature caused the adsorption of thorium to decrease. The adsorption of thorium by ferric hydroxide followed Freundlich isotherm.

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The elastic compliance and stiffness constants for hexagonal polycrystalline materials with sheet and fiber texture are calculated in Reuss-Voigt-Hill approximation by averaging corresponding properties of the single cystal weighted with the crystallites orientation distribution function(ODF). They depend only on the first five coefficients in the series expansion of ODF for sheet texture and two for fiber texture. Based on the ODF coefficients obtained by neutron diffraction, anisotropy of Young`s modulus was estimated for Zircaloy-4 sheet and tube samples as well as a Zircaloy-2 rod sample.

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By using the centrifugal atomization of rapid solidification process, the alloy powder which contained Sn and Si on the basis of monotectic Al-Pb system were fabricated. Morphology, size distribution, particle diameter, hardness were examined. To investigate distribution pattern of each element in the alloy powder, X-ray dot mapping of EPMA was used. And so, to know the solubility of Si by RSP, X-ray diffraction experiment was acted. The shape of the obtained powder particles were not globe-shaped but generally ligament, direct drop and irregular-shaped. The size distribution showed bimodal distribution which have two peak at 50㎛ and 200㎛. The microstructure for Si addition showed dendritic structure. From the solidification structure, the cooling rate of the alloy powder was calculated to be 10²∼10^5 K/S. Within the experimental conditions, it was found that the Addition elements were and thoroughly dispersed in the matrix. In the present work, the solubility of Si in a phase was about 4wt% by rapid solidification.

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