발간논문

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The degassing of Al melts, an essential part of Al foundry practice, has often an unpredictable result, as the effects of many factors are not well known. The effects of Mg content, initial gas content, amount of degassing tablets and moisture content of the air on C₂Cl_6 - tablet degassing of AlSi7Mg melt were investigated. The degassing efficiency decreases rapidly with increasing Mg content up to 0.1% and then remains constant. And it becomes gradually worse when the amount of degassing tablets for one plunging increases. The experimental results were analyzed statistically and an equation, C₂＝C₁exp(-kd), was formulated, to calculate the gas content C, after a degassing treatment with C₂Cl_6-tablet d, where k is a function of Mg content.

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A study on the reduction of stibnite by hydrogen in the presence of sulfur acceptors such as MgO and CaO was carried out at the temperature ranging from 450℃ to 500℃. Possible reduction mechanism for the reaction was discussed with the experimental kinetic data obtained in this investigation. The results obtained in this work are as follows: 1) The rate of reduction was increased by increasing the temperature and the amount of sulfur acceptor added and as being small the particle size. 2) The overall reduction rate of stibnite was controlled by the chemical reaction and the activation energy was found to be about 23 ㎉/㏖. 3) The effect of magnesium oxide on the reduction rate was greater than that of calcium oxide.

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A study on making the high strength Cast Iron by the small amount of copper addition in the ordinary component range was conducted, while tensile strength, hardness and microstructure by the variation of the amount of copper addition were investigated. The results obtained from this study are as follows; 1) When a small amount of copper was added to cast iron, the reifegrad became higher when the degree of S.C. was 0.88, the addition of copper increased the average reifegrad by 110. 2) The variance of tensile strength by addition of copper is as follows. In the case of 2.8% carbon, 1.9% silicon, the tensile strength was increased by addition of 0.75% copper and in the case of 3.1% carbon, 2.4% silicon, it was increased by addition of 1.5% copper. But, it was decreased beyond those copper values. In the case of 3.1% carbon, 2.4% silicon and 1.5% copper, the tensile strength was increased by 25% compared with that without copper addition 3) The variance of hardness by addition of copper is as follows. In the case of 2.8% carbon, 1.9% silicon, tensile strength was increased by addition of 0.75% copper and in the case of 3.1% carbon, 2.4% silicon, it was increased by addition of 1.0% copper. But, it was decreased beyond those copper values. In the case of 3.1 % carbon, 2.4% silicon and 1.0% copper, the hardness was increased by 14% compared with that without copper addition.

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A mathematical model was developed to describe the kinetics of gas-solid reactions. The model incorporates intergrain diffusion, intragrain diffusion, and surface reaction steps in series, and provides for variations in porosity and effective diffusivity of the reacting gas. For quantitative evaluation of the model, a particular system which oxidation of iron to wustite and reduction of wustite to iron were repeated in a cyclic manner to create the structual changes in the product layer was chosen. The prediction was found to agree reasonably well with results of reduction experiments. It should be however pointed out that the model proposed is not adequate to describe the oxidation process since the oxide layer formed is fairly compact.

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Piercing punches have been made from ausformed AISI H13 and M2 steels, and their service performance has been tested in actual nut manufacturing process. Ausformed H13 punches show increased service life by a factor of about 3 when compared with conventional M2 punches. This life improvement, which mainly results from reduced possibility of fracture at punch body, is primarily due to the increase of strangth by ausforming without deterioration of toughness. Metallographic observations indicate that, in ausformed H13 punches, the subsurface cracks initiated and propagated parallel to the worn surface, whereas, in conventional M2 punches, the cracks run inward from the surface. The life of ausformed M2 punches is about 2.5 times as long as that of conventional M2 ones. This result is associated with uniform dispersion of small carbides.

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Atomic cell model describing the heat of hydride formation of binary intermetallic compound is extended to the ternary intermetallic compound and some equations predicting the heat of hydride formation (ΔH) of ternary intermetallic compound are derived. Tested with relationship between ΔH and hydrogen equilibrium pressure, derived equations predict the trend of increase of ΔH well but fail to explain the difference between trend of ΔH of LaNi₄M type compound and that of La_(0.8)M_(0.2)Ni_5 type compound. To eliminate such difference, calibrated enthalpy change is suggested.

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