발간논문

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The effect of supercooling on the first stage graphitization of white cast iron has been studied by using the metal mold and sand mold which has various diameter for the purpose of studying various effects of malleable cast iron casted in metal mold. Following results are obtained. 1) The rate of the graphitization more increases with increasing thickness of metal mold in the metal mold casting process than in the sand mold casting process. 2) The rate of the graphitization increases more at the position near the mold wall both in the metal mold casting process and in the sand mold casting process, but the effect of which is more remarkable on the specimen tasted in metal mold. 3) The rate of graphitization increases with the annealing time both in the metal mold casting process and in the sand mold casting process, but the number of nodules are maximum at 40 min. in the metal mold casting process and 50 min. in the sand mold casting process, and afterward decreases. 4) The rate of the graphitization in white cast iron tasted in metal mold are maximized in the sample with 20㎜ thickness.

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Kinetics of the reaction of hydrogen with titanium and Ti-Al alloys have been studied in the temperature range of 670℃-800℃ at % Torr hydrogen pressure using thermogravimetric method. It is found that the reaction controlling step of the two systems is hydrogen diffusion in metals. The diffusion coefficients of hydrogen in pure titanium and Ti-6 at.% Al alloy are D(㎠/sec)=3.70×10^(-2)exp-(14,400±450)/RT) and D(㎠/sec)=2.79×10^(-2)exp-(17,400±410)/RT) respectively. Aluminum decreases makedly the diffusion coefficient of hydrogen. It can be probable explained by that aluminum decreases the interstitial site of titanium lattice.

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The effects of static stress and dynamic stress on hardenabilty and grain growth in medium carbon steel were investigated. Carbon steel bars were normalized at 925℃-1hr in order to eliminate the segregation of solute atoms and to relieve the residual stress, and then pre-strained in the range of 0 to 3.3%. Jominy bars were prepared for ø l"×L4". In order to observe pre-structure before quenching, grain growth with time was investigated at 800℃, 850℃, 900℃. Jominy end-quenching test was undertaken at constant cooling velocity. Hardenability was enhanced with increasing static stress. Activation energy for grain growth with static stress and dynamic stress was investigated. Austenite grain growth was much more accelerated with increasing static stress and dynamic stress. Grain growth exponent, ｎ was compared with static stress and dynamic stress. That value under dynamic stress was much more bigger than that under static stress.

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The activities of tin in liquid tin-antimony alloys were determined in the temperature range of 671 to 906K by means of the galvanic cell: Sn(l)｜Sn^(2+)(KCl-LiCl)｜Sn-Sb alloy(l). The entropies of formation of this alloy system were calculated from these results and the values of heat of formation measured by calorimetric methods. From the curvatures of the plot of activities and entropies versus the concentration of the alloys, it is suggested that the solid β phase has an influence on the thermodynamic properties of Sn-Sb molten alloys.

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