발간논문

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During the production of dual phase(DP) steels, intermediate phases such as acicular ferrite or upper bainite were frequently observed, which were very detrimental to the mechanical property of DP steels. The existence of undesirable phases could be adjusted by the enrichment and the redistribution of carbon in retained austenite after formation of polygonal ferrite during inter-critical annealing. In this study, the enrichment and the redistribution of carbon, which was a major strengthening factor, were measured by nano-hardness by changing holding time during inter-critical annealing. Indentation was conducted from center to near boundary of 2nd phases. The diffusion behavior of carbon during inter-critical annealing between DP steel and plain carbon steel was compared in order to understand the effect of Si on behavior of carbon and phase transformation.

keyword : dual phase steels, carbon enrichment, nano-indentation

This study is aimed at finding its applicability to elasto-plastic damper manufactured by Fe-Mn damping alloy in structure building. Almost existing elasto-plastic damper has been effective for plastic design against the earthquake. On the other hand, elastic design against wind load has been ineffective, because research of suitable material has been imperfect. Accordingly, we make an experiment of increment cyclic loading test with controlling 6-typed displacement to confirm the applicability of Fe-Mn damping alloy to the elasto-plastic damper. In this result of this test, we confirmed the steel plate damper manufactured by Fe-Mn damping alloy showed 3.1 times energy absorption capacity in the skeleton part compared with SS400, 2.0 times capacity in the Bauschinger part and 2.4 times capacity in the total part. Therefore, the steel plate damper with Fe-Mn damping alloy is available for elastic and plastic condition, that is, it can be designed against resisting the earthquake and wind load.

keyword : Fe-Mn damping alloy, energy absorption capacity, Load-displacement, steel plate damper, specific damping capacity

In this study, rapid solidification experiment was conducted for understanding of dent defects formed during strip casting of TWIP steels. Rapid solidification experiment reproduced dent defects of the TWIP steel strips, and dents were generally located in valleys of shot blasted roughness on the substrate. The rapid solidification experiment results reveals that the number of dipping, Mn content inside melt, and surface roughness on the substrate affected the depth and size of dents formed on solidified shell surfaces. Dents were closely related with entrapment of atmosphere gases and their thermal expansion in valleys of the substrate roughness. Longitudinal grooves and shot blasting texture on the substrate were suggested as a good method to prevent dent defects since they prevented the thermal expansion of gases and were continuously served as for gas escaping channels.

keyword : twin roll strip casting, TWIP steel, roughness, solidification, dent defect

A simulation of energy and mass balance for smelting reduction of steelmaking slag was carried out to diagnose the possibility of ressurection of steelmaking slag. The proposed smelting reduction slag compositions from energy & mass balance indicated that the viscosity of slag was to be a process controlling step to maximize reduction process efficiency. Therfore, the viscosity measurements of smelting reduction slag were carried out and discussed. Present viscosity measurement indicated that the viscosity of slag was depended on basicity and FeO content of slag, which affects on increase of viscosity with decreasing temperature was Al2O3 content in slag. The slag composition for optimum smelting reduction operation would be proposed to control in C/S=2.3, l0mass%Al2O3-8mass%MgO-15mass%FeO. Dephosporizing & stirring efficiency of proposed slag system was discussed.

keyword : slag, smelting, reduction, viscous

The reduction behaviour of carbon composite briquettes of steelmaking by-products containing iron oxide, EAF(electric arc furnace) dust and mill scale, was investigated within the temperature range 1,000℃ to 1,550℃. The reduction degree of the briquettes depending on the reaction time was evaluated by means of the off-gas analysis. The reduction degree of EAF dust was higher than that of mill scale at low temperature not exceeding 1,250℃. But EAF dust and mill scale showed similar reduction behaviour at elevated temperature above 1,250℃. The rate constants of the reduction reaction of EAF dust and mill scale briquettes were determined for the initial stage of the reaction at which the rate is determined by the chemical reaction. Arrhenius plot of the reaction rate constants with the reciprocal absolute temperature showed discontinuities at temperature of 1,238.1℃ and 1,279.3℃ for EAF dust and mill scale briquette, respectively. The rate equations of the reduction reaction agreed well with experimental values.

keyword : EAF dust, Mill scale, Carbon composite briquette, Reduction degree, Reduction rate, Activation energy

Texture character and strength in the Cu film are a function of sublayer material, film thickness, bath chemistry, deposition parameters and twin boundary development that is also related to processing conditions and film geometry. The present work summarizes grain growth behavior and texture development depending on deposition methods(PVD, electro-deposition) and annealing conditions in the Cu thin films of 480,850 nm thickness deposited on a Ta(25 mn)/Si wafer using EBSD(electron backscatter diffraction) in FE-SEM. Each sample was annealed in vacuum at 200, 300, 400, 500℃ for 1 hour. The grain growth and crystallographic texture are described and analyzed in connection with film thickness, deposition methods and annealing temperature having an influence on the annealing texture development.

keyword : Cu films, grain growth, twin, EBSD, annealing texture

Rhenium thin films have been deposited on a (100) Si wafer by RF magnetron sputtering. Subsequently, the Re thin films have been annealed in the vacuum quartz tube in the temperature range between 800℃ and 1200℃. After the heat treatments, SiO2 layers have been detected between Re thin film and Si substrate. To reduce the residual oxygen, the vacuum heat treatments have been done using Ta foil as a getter material in the temperature ranging from 800℃ to 1,200℃. Polycrystalline ReSi1.75 thin films have been formed on the Si substrate after the samples annealed above 1,000℃ with the Ta foil. When the Ta foil used in heat treatments, the formation of SiO2 in the interface between Re thin film and Si substrate was prevented, consequently, polycrystalline ReSi1.75 thin films could be formed on Si substrate even in the high vacuum.

keyword : ReSi1.75, RF magnetron sputtering, transition metal suicides, thermoelectric materials, Ta getter