발간논문

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The formation of shrinkage cavities during solidification is a serious defect in the spheroidal graphite cast iron castings. It is considered that the shrinkage cavities are formed as a result of the expansion force of spheroidal graphite cast iron during solidification, and the force was measured. The results obtained through this experiment are as follows: 1. The highest force during the solidification in the spheroidal graphite cast iron is 36-37kgw (X component of the force) 2. The force increasing gradient df/dt, in the spheroidal graphite cast iron of hyper eutectic composition is 167gw/sec. when eutectic reaction es occres

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There are many kinds of no bake self-hardening method using sodium silicate. When sodium silicate solution is mixed with calcium-orthosilicate powder hardening reaction is occured, which is based for self-hardening method at room temperature. The compression strength, surface stability and residual strength of mold are so related to the molecular ratio of sodium silicate and the content of calcium-orthosilicate powder that these properties are tested and studied, especially using domestic silicate sand, varing the content of 2CaO-SiO₂ from 1% to 4% at 7% of sodium silicate mixed. The results obtained in this study are as follows, 1) The compression strengths are getting still higher, along to the contents of 2CaO-SiO₂ up to 4% untill about 12 hours and after that time the strengths are inverted. 2) The final compression strength is much higher in case of low contents of 2CaO-SiO₂ and low molecular ratio. 3) The surface stability is not so varied along to the change of 2CaO-SiO₂ content and the molecular ratio. 4) The optimum properties can be obtained form ZIN HAE silica sand mixture at 7% of sodium silicate, molecular ratio 2.3 and 2% to 3% of 2CaO-SiO₂ powder.

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With published solubility of hydrogen in the α-phase and β-phase of binary alloys of Zirconium with various alloying elements, the interaction coefficient of each alloying element is calculated at each temperature up to 5 atomic percent of alloying elements. The temperature dependence of interaction coefficients of niobium, indium, titanium, antimony, oxygen in α-phase and niobium in β-phase is discussed in the temperature range of 600℃-800℃ and the temperature dependence of interaction coefficient of above elements is calculated. The physical meaning of interaction coefficient is discussed and the terminal solubility of hydrogen in the α-phase of hypothetical multicomponent alloys of Zirconium has been predicted by means of it.

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Magnetic and mechanical properties of Fe-Cr-Co-R (R: rare earth metals Y and Sm) magnet alloys were studied and the mechanism bringing about their characteristics is closely examined through the heat treatment. A number of Fe-30%Cr-25%Co-(1∼2)%R quaternary alloys for specimens were prepared by arc melting under a protective atmosphere and specimens were annealed for various times at the aging temperatures between 100℃ and 800℃. It was found that the magnetic and mechanical properties of Fe-Cr-Co-R quaternary alloys annealed between 500℃ and 600℃ were the best and superior to Fe-Cr-Co ternary alloys. Especially, the coercive force of Fe-30%Cr-25%Cr-2% Sm was remarkable compared to Fe-Cr-Co magnet alloys and the maximum energy product 3.3 MGOe was obtained at the state annealed at 580℃ and for 16hrs. Temperature difference between the peak of coercive force and hardness of alloys was almost nothing, which was less than the temperature difference in many precipitated magnetic materials. It may be concluded that the significant increment of coercive force and tensile strength between aging temperatures 500℃ and 600℃ of these alloys is due to the modulated structure of fine (Fe-Co-R) phases with a high saturation magnetization and non-ferromagnetic Cr rich phase produced by the spinodal decomposition.

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Rates of dissolution reaction of natural sphalerite with aqueous sulfuric acid were studied in the concentration range of 0.1N to 10N and over a temperature range of 20℃ to 90℃. The effect of iron on the dissolution rate wes investigated by using three sphalerites at the different iron levels of Fe 13.96%, 0.33% and 0.11%. In the absence of depolarizer, the dissolution reaction a controlled by the surface reaction, and the rate could be expressed in terms of the spherical geometry for the initial stage of the reaction; 1-(1-R)^(◎)=kt An activation energy for tine dissolution reaction was found to be 11 ㎉ regardless of the iron level in sphalerite. A quantitative picture of the reaction mechanism was given based on rate studies and etching tests. Galvanic dissolution may be an important factor affecting the reaction rate of natural sphalerite.

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The effect of local solidification time(θ_f) and solute contents on the secondary dendrite arm spacing(d), and the effect of solute contents and cooling rate on the dendrite morphology transition in the hypoeutectic constitution of Al-Cu binary alloys by unidirectional solidification have been studied. And the following relationship is obtained; d=K·θ_f^(0.37) where, K is varied by the solute contents. The critical Cu contents where the dendrite morphology changes from plate-like to rod-like moved from high solute contents to low solute contents as the cooling rate increased. This fact was interpreted in terms of constitutional supercooling.

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The amount of retained oxygen and it`s relation with the formation of graphite in the gray cast iron melted with the medium frequency induction furnace were investigated. And also the effect of retained oxygen on the inoculation by adding mill scale as the oxidizing agent at 1,450℃, 1,500℃, and 1,550℃ respectively were studied. The results were as follows: (1) The amount of retained oxygen was approximately 80-100 ppm (2) The number of graphite nucleus was decreased as carbon equivalent decreases. The number of nucleated graphite was decreased and the hardness was increased, as increasing the amount retained oxygen. (3) when 3% aad 6% mill scale, respectively, were added into the molten gray cast iron, the activation energy for the graphite nucleation was 15,000 ㎈/㏖ and 21,000 ㎈/㏖, respectively. (4) The shape of graphite, as the amount of retained oxygen increases, was changed from coarse flake, rossete to eutectic gradually.

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The present work is concerned with the effects of molding material, gating system, melting condition & pouring temperature on the soundness of Cu-alloy castings. These effects were evaluated by the measurements of solidification rate, leakage, chemical composition and mechanical properties. Because the soundness of castins not only depend on solidification rate, chemical composition and mechanical properties, but also depend on leakage of hydraulic pressure. The castins were poured in three different mold; natural bonded sand, synthetic sand, and resin coated sand. A 5㎏ melt of each alloy was made by degassing with Cu-P alloy in cryptol furnace under various conditions to determine the effects mentioned above. On the basis of these experimental results, favorable condition of casting process was proposed as follows. 1. Synthetic sand mold was more effective than the others. 2. Unpressurized gating system having screen at juncture between the runner and ingate would be more desirable in order to avoid the turbulence and non-metallic inclusion such as dross and sand. 3. When scraps were only charged degassing was desirable after melting under oxidizing condition. This reason may be rationalized by equilibrium curve of oxygen and hydrogen proposed by Allen & Hewitt. 4. The optimum pouring temperature was found to be 1150℃.

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