발간논문

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Fe-28%Ni alloy was subjected to the repeated thermal cycling for the γ⇔α`, their effects on the transformation temperatures and tensile properties were investigated. The Ms temperature was singnificantly lowered with increasing the numbers of cyclic heat treatments, particularly at the first cycle. On the other hand, the Md temperature was slightly raised. In the range between Ms and Md temperature, the elongation peak was appeared and decreased by cyclic heat treatments. As the test temperature was remarkably lowered in this range, the yield strength of the cyclic heat-treated specimens increased first and then decreased but the ultimate tensile strength was continuously increased. The increment of the yield strength caused by cyclic heat treatments was large, but in case of the ultimate tensile strength was not so.

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The origin of elongated ferrite grains that result from hot rolling has been studied in 3% Si-steel. Four-stage hot rolling and single-pass hot rolling practice were carried out at the reduction range 20 to 50% over the temperature range 1000 to 1150℃ to investigate the microstructural evolution during the finishing rolling. It has been found that the microstructural evolution during the finishing rolling results mainly from dynamic recrystallization in the initial few passes, while dynamic recovery operates dominantly in the final few passes.

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The effect of carbon additive on the sinterability and the micro-structure of P/M-T1 grade high speed steel was investigated. The additional carbon added to the nominal composition of T1 grade high speed steel was very useful for adjustment of carbon content as well as for achievement of full densification, so far as this steel should be produced by conventional P/M technique. The optimal sintering condition was related closely with the excess carbon content. In the present work, the optimal condition was proved that the sintering temperature was 1310℃ for the specimen with 0.3w/o excess carbon.

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The effects of cobalt contents on the substructures and textures of Ni-Co alloys deformed by rolling have been studied. The substructures of Ni-Co alloys rolled 50% and 93% show a strong tendency to form cells with decreasing cobalt content, and the cell size becomes smaller with increasing deformation degree for the same alloys. The rolling textures of all the Ni-Co alloys rolled 93% are mainly composed of (220) plane parallel to the rolling direction, independent of the level of cobalt content.

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Titanium was deposited onto 430 stainless steel substrate by means of chemical vapor deposition (CVD) from TiCl₄and H₂gas mixture. Effects of temperature and flow rate of reactant gas on the deposition were investigated. Amount of Ti-deposition was increased linearly with respect to the time at constant temperature and TiCl₄, partial pressure. When the total flow rate was below 500ml/min, the deposition rate of Ti was increased linearly with the square root of the total flow rate, whereas above 500㎖/min, the deposition rate of Ti remained constant. Results revealed that below 500㎖/min the deposition rate was controlled by diffusion process while above 500㎖/min, controlled by the surface reaction. It is also postulated that below 1100℃ the deposition reaction is controlled by the surface reaction (activation energy of 36.3㎉/mole), and above 1100℃ the process is controlled by the adsorption of the reactant species TiCl₂(activation energy of 12.7㎉/mole).

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