• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.238-244
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• 2017

Plasma ion nitriding has been widely used in various industries to improve the mechanical properties of materials, especially stainless steels by increasing the surface hardness. It has the particular advantages of less distortion compared to that in the case of hardening of steel, gas nitriding, and carburizing; in addition, it allows treatment at low-temperatures, and results in a high surface hardness and improved corrosion resistance. Many researchers have demonstrated that the plasma ion nitriding process should be carried out at temperatures of below $450^{\circ}C$ to improve corrosion resistance via the formation of the expanded austenite phase(S-phase). Most experimentals studied to date have been carried out in chloride solutions like HCl or NaCl. However, the electrochemical characteristics for the chloride solutions and natural seawater differ. Hence, in this work, plasma ion nitriding of 304 stainless steels was performed at various temperatures, and the electrochemical characteristics corresponding to the different process temperatures were analyzed for the samples in natural seawater. Finally the optimum plasma ion nitriding temperature that resulted in the highest corrosion resistance was determined.

• Tribology and Lubricants
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• v.27 no.6
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• pp.308-313
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• 2011

In this study, friction tests were performed in order to investigate the effect of sliding velocity and normal load on the friction characteristics of DLC (a-C:H) and WC/C (a-C:H:W) using a ball-on-disk type friction tester. DLC and WC/C were deposited on AISI 52100 steel balls. Friction tests against carburized SCM 415 Cr-Mo steel disks were carried out under various sliding velocity (0.1, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50 and 100 mm/s) and normal load (2.4, 4.8 and 9.6 N) conditions while the relative humidity was 20~40 % R.H. and air temperature was $16{\sim}24^{\circ}C$. As results, kinetic friction coefficients of DLC and WC/C were obtained under each test condition. The results show that the kinetic friction coefficients of DLC and WC/C generally increase with the increase in sliding velocity. And, under the same sliding velocity condition, the kinetic friction coefficients are almost constant regardless of normal load. In addition, the kinetic friction coefficients of DLC are lower than those of WC/C under the same test conditions.

• Journal of the Mineralogical Society of Korea
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• v.20 no.4
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• pp.231-245
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• 2007

The forged iron axe of the middle 3rd Century found in the No. 2 wood-framed tomb from the Hwangseongdong site, Gyeongju is rectangular on the plane level. The iron axe shines in met-allic luster, which is light grey with pale creamy tint. The result of X-ray diffraction analysis shows that the axe consists of magnetite and geothite, which can explain why the composition and texture of the original ore has been kept intact. There are fine-grained quartz, calcite, mica, magnetite, amphibole, unknown tungsten minerals, pyroxene and olivine inside the axe. Those must be the impurities that they failed to remove in the thermal treatment process. Generally, the iron axe consists mainly of pearlite texture coexisting ferrite and cementite, and show high carbon contents with homogeneous distribution. It can be interpreted the axe was carburized after the material was made to resemble pure iron. The decarbonization work didn't go well along the process marks. Crude ores of the iron axe are possible utilized by magnetite from the Ulsan mine on the basis of the occurrences and inclusions. It's estimated that the original ore was bloom produced in low-temperature reduction and formed around in $727^{\circ}C$, which is eutetic temperature.

• Journal of Conservation Science
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• v.38 no.3
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• pp.217-233
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• 2022

The remains found in Geumcheok-ri, Gyeongju are located in close proximity to the Ancient Tombs in Geumcheok-ri, Gyeongju (Historic Site) which were built between the late 5th and early 6th centuries, and these tombs are known to belong to the powerful rulers of that area. Using metallurgical techniques, this study was conducted on the iron objects obtained from the excavated remains in Geumcheok-ri, Gyeongju which are presumed to have a close relation to the nearby ruins that played an important role in the growth of Silla. To identify differences in manufacturing techniques based on the purpose of the iron objects, eight objects were selected after classifying them by use and the microstructure and non-metallic inclusions were investigated. The analyses results confirmed that the manufacturing process involved forging iron with a high or low carbon content to produce a particular shape, and that the carburization process was applied to iron post forging a shape to increase its strength when necessary. The mechanical properties were improved by selectively applying the steelmaking method and the heat treatment technique considering the functions of the parts, and the low temperature reduction was applied to the smelting process. Furthermore, in comparison with the iron objects excavated from the remains located in the center of Gyeongju and its outskirts, it is confirmed that there is similarity in the smelting and manufacturing techniques between these objects.