발간논문

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The form of unsolute particles and variations of hardness and electrical conductivity with Cr/Zr contents were investigated in Cu-Cr-Zr alloys. The volume of unsolute particles increased with Cr and/or Zr contents and the unsolute particles were revealed pure Cr and Cu-Zr compounds. Within the limit of total solubility of Cr and Zr, the increase of hardness and the decrease of electrical conductivity were steep with Cr and/or Zr contents. Beyond this limit the change of hardness and electrical conductivity was not significant with Cr and/or Zr contents. When total content of Cr and Zr was constant beyond the limit of solubility, electrical conductivity decreased with Zr content while the change of hardness did not occur.

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Effects of melt treatment with phosphorus and/or strontium on the microstructures have been investigated in hypereutectic Al-Si alloys. Phosphorus made finely and uniformly distributed primary Si but did not affect the eutectic Si. Strontium addition changed the morphology of eutectic Si from acicular form to fibrous one while it coarsened the size of primary Si. Simultaneous addition of phosphorus and strontium had a deleterious effect on the refinement of primary Si. Further, it reduced the modification effect of strontium. When phosphorus was added to the strontium treated alloy during remelting, the morphology of eutectic Si was changed to fibrous form but the primary Si was coarsened. Meanwhile, when strontium was added to the phosphorus treated alloy during remelting, primary Si was refined and the modification effect of Sr was also maintained.

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It is well known that the quality of slab and the productivity of continuous casting are directly linked to controlling the hydrodynamical state of liquid steel in the mold. The EMBR creates a transverse static magnetic field in the mold. Interaction of this field with the liquid steel flow creates a braking force. This braking force is expected to brake and redistribute the flow of the steel jets from the nozzle and suppress vorticity, turbulence and finally results in various beneficial effects. In this research, a computer program that can calculate the flow of molten steel in continuous slab caster equipped with EMBR was developed. A series of parametric studies using this computer program could help the understanding of the effects of EMBR and provides the fundamental data for the operation of the EMBR equipped caster, and will give understandings how EMBR works.

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The elevated temperature creep properties and microstructural stability of RS/PM Al-10Fe-1.3V-2Si-1Ti-1W(wt.%) alloy have been investigated. The alloy showed high stress exponent of 12 to 18 and activation energy of 237 to 808 kJ/㏖, which was strongly dependent on the temperature and stress. The unusual creep behavior of the dispersion strengthened alloys cannot be described satisfactorily by current creep laws, Recently, Ro¨sler and Arzt proposed a new model assuming thermally activated dislocation detachment from dispersoids exerting an attractive force. In the present study, experimental evidence was achieved for the presence of attractive interaction between the dislocation and the dispersoids using TEM observations. The creep behavior of the alloy was analyzed using the model proposed by Ro¨sler and Arzt, and the experimental data were consistent with the prediction based on the model. It has been confirmed that the high temperature deformation of the alloy was dominated by the dislocation creep at the temperature range of 400 to 480℃, but the diffusional creep at the interface between powders also contributed to the deformation above 430℃.

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Austenite phase in metastable Fe-Cr-Ni ternary stainless steels was fully transformed to martensite(α`) phase by 90% cold rolling and this martensite single phase reverted to austenite again at temperature range from 773 to 1073K. The mixed phase structure consists of reversed ultra-fine austenite grains with the diameter of 0.5 ㎛ and remained α`. Their mechanical properties were investigated as a function of α` content and austenite stability. The main results may be summarized as follows : (1) The good combination of high yield strength over 800MPa and elongation near 20% was obtained from the mixed structure containing a higher content of α`, as Ni and Cr contents are lowered. (2) In the mixed structure, elongation was greatly affected by the TRIP behavior in the initial stage of deformation. (3) The ultra-fine graining of austenite more stabilized the mixed structure. (4) The abrupt drop of elongation in the mixed structure occurred at a limited content of α` in according to the difference of austenite stability. This phenomenon was well explained by the criterion equation of the plastic stability.

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The new lead plant based on the QSL technology has commissioned at Onsan Refinery of the Korea Zine Co., Ltd. in May 1992. After the start-up of QSL plant, it turned out to be capable of treating various ranges of raw materials within a relatively short period of time. In this paper, the distribution behavior of lead, arsenic, bismuth, copper and zinc in QSL reactor is discussed with thermodynamic evaluation. Major parameters to control the operation the QSL reactor, separated by oxidation and reduction zones, are the oxygen potential in the oxidation zone and the ratio of CO/CO₂ in the reduction zone respectively.

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In the W-halogen lamp SOI-ZMR, a heat equation with moving heat source was analytically solved. However, the previous analytical solutions do not satisfy two boundary conditions at │x│ = ∞. Therefore, to satisfy the two boundary conditions, the analytical solutions are modified in this study. Even at sufficiently large │x│, the modified analytical solutions correspond very well to numerical solutions obtained with FDM.

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The vacuum brazing of AlN to Cu with Cu and Ag based brazing alloy containing Ti has been carried out to investigate the wettability and interfacial reaction. Binary Cu_(78)Ti_(22)(CT), Ag_(98)Ti₂(AT) alloys and ternary CT-5wt.%X, AT-1wt.%X(X=Al, Ni, Mn) alloys showed good wettability on AlN and led to the formation of TiN layers at the interface. 4-point bend strength of the joint has increased with bonding temperature and showed maximum value, and then decreased with temperature. The highest bond strength of 35 kgf was obtained at the brazing condition of 900℃/1800sec with AT alloy. The failure of this joint was initiated at the interface between AlN and TiN layer and then proceeded alternately through the TiN layer and AlN.

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