발간논문

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The oxidation mechanism of tuyere copper in a blast furnace was studied in oxidation experiments at temperatures of 600 to 900℃ under oxidizing atmospheres of O₂(0.01-0.04 atm), CO₂(0.01-0.03 atm) and O₂＋ CO₂mixed gases. In the case of oxygen atmosphere, the oxidation rate constant of tuyere copper was linearly dependent on Po_₂^(1/8) and the activation energy was 33.3㎉/mole. Under CO₂atmosphere, the oxidation rate constant was proportional to Pco₂and the activation energy was 20.3㎉/mole, When O₂＋ CO₂mixed gas was used, the gas composition had little influence on the oxidation rate constant and the activation energy was 35.97±0.44㎉/mole. It was shown that a double layer composed of CuO and Cu₂O was formed under oxygen and mixed gas atmospheres, wheres, a monolayer of Cu₂O was formed under carbon dioxide atmosphere. (Received August 13, 1992)

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Solid and liquid phase sintering behaviors of ball-milled 75W-25Cu have been studied by using a dilatometry technique. The ball-milled 75W-25Cu was prepared by high energetic ball milling under argon atmosphere of 1 atm with duration times of 50 to 400 hrs. The sintering was performed in the dilatometer under flowing hydrogen atmosphere with a heating rate of 3℃/min. To compare with the ball milled 75W-25Cu, blended 75W-25Cu was also prepared and sintered. Sintering shrinkage, dl/1, increased with increasing milling time from 50 to 400 hrs. The shrinkage versus temperature plots of the ball-milled 75W-25Cu can be divided into three regions, while for that of the blended 75W-25Cu two regions. The characteristics of ball-milled 75W-25Cu were analyzed by energy dispersive spectroscopy (EDS), differential scanning calorimeter(DSC) and scanning electron microscopy (SEM). The considerable grain growth of W particles was observed during the liquid phase sintering of the ball-milled 75W-25Cu. From these results, the solid and liquid phase sintering behaviors were discussed in terms of the size, the stored energy, and the distribution of W and Cu particles embedded in the ball-milled 75W-25Cu composite powders. (Received August 18, 1992)

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Kinetics of the decarburization reaction in the ultra low carbon ranges under reduced pressure was studied in steel, using both a vacuum induction melting furnace and the RH of 300ton. The optimum conditions for getting carbon content of 20ppm within the RH treatment of 15minutes are as follows: 1) The pressure of vessel should be less than one torr in five minutes after the start of decarburization. 2) Ladle slag entrained into vacuum vessel shows a deFrimental effect on decarburization during the RH treatment. The slag decreases the decarburization rate and increases the carbon content by 10ppm after the treatment. 3) Carbon and oxygen contents of 200-350ppm and 500-850ppm, respectively before the RH treatment are required. 4) The Ar gas flow rate should be more than 2400 Nℓ/min during RH treatment. (Received July 22, 1992)

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In the steel D&I can-making industry, there has been a tendency of increasing the punch speed to meet the needs of high productivity. Owing to high punch speed, however, produced can occasionally shows dull and scratched surface which is called frosting phenomenon. In the present work, to investigate the effects of various factors on the frosting, steel D&I can-making was carried out with facilities of commercial line and ironing simulator of lavoratory scale. The frosting seemed to be influenced by the number of ironing steps and the characteristics of coating layer of tinplate. Tinplates resulting in lightly frosted cans were observed to have less surface oxides and Fe＋Sn alloyed layers than those of heavily frosted cans. They had also developed preferred orientation of (101) plane. In laboratory scale experiments, it was found that the frosted area was decreased with decreasing thickness reduction ratio of final ironing die.

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The Upward Continuous Casting process which manufactures near-net shaped crystals directly from the melt has been improved in order to reduce the cost of products. Growth of plate and tube shaped crystals using the U.C.C. process was carried out with tin. Near-net shaped tin plates and tubes have been produced with the newly developed mold. The effects of process parameters on the size and the shape of the crystal were studied:these were the meniscus height(S), the length between the top surface of the mold and free surface(H), the mold temperature, and the pulling speed. Of these S and H were the most important parameters in determining the crystal shape stability. The U.C.C. process was compared with other shaped growth methods to determine its growth stability. It can be concluded that the U.C.C. process will find applications in the growth of various shaped crystals.

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A sumberged rotating disk technique has been employed to study a reaction mechanism of Wu¨stite in molten pig iron and the reaction was followed by a volumetry of product gas. Rates of reaction have been measured between 1485K and 1611K and also in the disk speed of 200rpm to 800rpm. The reduction rate of wu¨stite was strongly dependent upon temperature, rather than the rotating speed. A kinetic model was developed to describe the rate of reduction of iron oxide in liquid pig iron. The model incorporates carbon diffusion, diffusion-out of reduced iron and surface reaction steps in series. Experimental results showed reasonable agreement with the theoretical predictions. The apparent activation energy of the surface reaction was found to be 41㎉/mole. The reduction of Wu¨stite was controlled by the surface reaction at the initial stage and the diffusion-out process of the reduced iron to liquid pig iron became the effective rate control step at the later stage of reaction.

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This study was designed to investigate the nonshearable behavior of Mn-dispersoid in Al-Zn-Mg alloy. In order to examine whether Mn-dispersoid behaved nonshearable or shearable, the Bauschinger stress was obtained on the first hysteresis loop by low cycle fatigue test. Comparing our results with other`s Mn-dispersoid dispersed in Al-Zn-Mg alloy was found to be the nonshearable particle. It was thought that these results could be certainly explained by the modified Orowan mechanism for the Bauschinger effect.

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