• Korean Journal of Materials Research
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• v.17 no.3
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• pp.179-183
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• 2007

A plate heat exchanger (PHE) normally uses vacuum brazing technology for connecting plates and fins. However, the reliability of high temperature brazing, especially with nickel-based filler metals containing boron the formation of brittle intermetallic compounds (IMCs) in brazed joints is of major concern. since they considerably degrade the mechanical properties. This research was examined the vacuum brazing of commercially SUS304 stainless steel with BNi-2 (Ni-Cr-B-Si) filler metal, and discussed to determine the influence of brazing temperatures on the microstructure and mechanical strength of brazed joints. In the metallographic analysis it is observed that considerable large area of Cr-B intermetallic compound phases at the brazing layer and the brazing tensile strength is related to removal of this brittle phase greatly. The mechanical properties of brazing layer could be stabilized through increasing the brazing temperature over $100^{\circ}C$ more than melting temperature of filler metals, and diffusing enough the brittle intermetallic compound formed in the brazing layer to the base metal.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.3
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.439-446
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• 2016

In 2015, a fin tube (Cu-Ni 70/30 alloy) of package type heat exchanger for navy vessel was perforated through the wall which led to refrigerant leakage. This failure occurred after only one year since its installation. In this study, cause of the failure was determined based on available documents, metallographic studies and computational fluid dynamics simulation conducted on this fin tube. The results showed that dimensional gap between inserted plastic tube and inside wall of fin tube is the cause of the swirling turbulent stream of sea water. As a result of combination of swirling turbulence and continuing collision of hard solid particles in sea water, erosion corrosion has begun at the end of inserted plastic tube area. Crevice corrosion followed later in the crevice between the outer wall of plastic tube and inner wall of fin tube. It was found that other remaining tubes also showed the same corrosion phenomena. Thorough inspection and prompt replacement will have to be accomplished for the fin tubes of the same model heat exchanger.

• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.235-240
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• 2010

The evolution of microstructure and phases of Mg-10Al-Mn alloy by cooling plate method during homogenization treatment have been investigated with metallographic analysis, scanning electron microscopy and energy dispersive spectroscopy. The ingots used for this experiment were prepared by cooling plate and homogenization heat treatment was performed at 300 and $400^{\circ}C$ for various holding times (0, 1, 4, 8 and 12h). The casting ingots were consisted of the fine grains and eutectic phases. And, these eutectic phases were dissolved into the matrix during homogenization treatment at $400^{\circ}C$ but the lower temperature (at $300^{\circ}C$) did not be.

• Journal of Korea Foundry Society
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• v.26 no.6
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• pp.258-266
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• 2006

The purpose of this study was to investigate the effects of silicon and nickel additions that influenced the impact and tensile properties of heavy section as-cast ductile irons for wind mill. Based on the results of the metallographic analysis and the mechanical testing on the 2.0 wt.%Si (LS group) and 2.4 wt.%Si (HS group) ductile irons, which contains 0.0, 0.3, 0.6 and 0.9 wt.%Ni, respectively, the following conclusions could be obtained. The nickel additions increased the tensile properties, the microhardness of pearlite, and the pearlite fraction of matrix for the specimen with the same silicon content. The mechanical properties of LS group specimen were in the range of the specification for the ductile iron wind mill castings. The LS group specimens showed higher absorbed impact energy at room temperature and $-20^{\circ}C$ than that of the HS group specimens. However, the absorbed impact energy at $-20^{\circ}C$ for the HS group specimens was observed to be sharply decreased under 10 J by addition of the nickel.

• Journal of Conservation Science
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• v.16 s.16
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• pp.64-76
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• 2004

This study was performed by chemical analysis and metallographic observation. Chemical properties were analized by ICP, XRD and SEM-EDS and slag structures were observed by microscope and SEM. Total Fe amounts in A, C area of slag can be observed $39\~45\%$ by chemical analysis results. It was average of acient times. CaO was $3\~8\%$. It's not plentiful but we think that was artificial. Ti was found in A area a little, and Ti, V were found in C area so much. The compounds, as if Fayalite, Wustite, Magnetite, Ilmenite, Pseudo-brookite, Ulvospinel, Forsterite, Fephroite, Olivine were observed in the result XRD. These structures were also observed in microscope and SEM image. Therefore, The furnance of A area usually used an iron mine, An Iron furnance of C area considered it which refined using a raw iron mine and a raw iron sand.

• 보존과학연구
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• s.27
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• pp.165-180
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• 2006

The research was conducted to understand type of iron used by those who lived at dwelling site of Yangsoo-ri in between the first century B.C. and the first century A.D. to make steel products and their technique such as steel making process and heat treatment, based on micro structure information obtained through microscopic metallographic structure analysis with SEM-EDS of six steel productsexhumed at the site. Key findings are summarized as below. In the sense that Si-Ca-Al style and less than 0.5% of Ti were found in the non-metallic inclusion, the material used for forged iron ware was magnetite resolved in that. It is, however, unclear whether magnetite was resolved at high temperature or at low temperature. Microscopic structure analysis revealed that forged steel products were made through repeated hot working, the technique of molding by hitting after heating in the process of resolving and molding iron. As a result, the iron used here for the products was not the iron ore which was produced through resolution from discarded cast iron axe, ingot iron. It is probable that to make those steel products, disposed-of cast iron was reused after being molded by decarburizing. Although a few of relics were analyzed for the research, they were of critical importance in defining the process of ironware production from the first century B.C. and the first century A.D. at the Yangsoo-ri region. Judging from the iron from A-19 dwellingsite, it is possible to conclude that the iron was manufactured from cast iron decarburized and yet more research has to be done into relics yetto be exhumed in order to ascertain the finding. All of these findings are believed to play a critical role in further studies to define the steel-manufacturing technique used on the central Korean peninsular in the ancient times.

• 보존과학연구
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• s.22
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• pp.115-132
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• 2001

No. 3 Tomb of Bogam-ri, in Naju City, Chollanam-do Province, was a site excavated and inspected from 1996 to 1998 and had a various grave forms, including jar-coffins, stone-chambers and stone-cists. Although most of the metal artifacts excavated from it were severely corroded, we could implement microstructure investigation by collecting samples from the iron axes, iron coffin-nails and iron clamps in which the metal parts were remained. The metal structures were inspected by using metallographic microscope and SEM, and fine components analysis was implemented by ICP. To examine the hardness differences in accordance with the structure distribution, we measured the hardness by structures with Vickers hardness testing machine. As a result of the metal structure inspection, most of them were pure iron, ferrite, and also pearlite, cementite and widmannstaten structures were displayed. We could confirm carbonization was formed on the surface of the iron axes-B, iron coffin-nails-B, and iron clamps-A. There was no carbonization in the rest of the artifacts, and it is not certain that whether the carbonized parts were peeled off through extreme corrosion or they were not carbonized when they were made. In the particular part of a blade, the quality of the material was strengthened through processing. Due to the processing re-grain was caused and fine grain particles were formed. As a result of the ICP component analysis, there were no addition atoms because pure irons were used as materials. In the mean time, No. 17 jar-coffin where the iron axes-A are excavated, is chronologically ordered as from the late-fourth century to the mid-fifth century, and No. 1 and No. 2 stone chambers, where the rest of the artifacts were excavated, as the early-sixth century. It was difficult to relate the periodic differences with the manufacture technique artifacts which we inspected because there were no distinct characteristics of the manufacture technique of the metal structures and it is impossible to conclude the artifacts and sites are at the same period although their periods are different.

• 보존과학연구
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• s.21
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• pp.77-99
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• 2000

Tumuli located in Chodang-dong in Kangreung City are sitesexcavated by the Museum of Kangreung University in 1993.Ofthese sites, a gilt bronze crown and gilt bronze sword with ring pommel with a tri-leaf ornament were excavated from the B-16tumulus. Underneath the gilt bronze crown was the gilt bronzes word with ring pommel with tri-leaf ornament, and these artifacts were treated with Polyurethane foams on the spot followed by special measures for conservation. This manuscript describes measures for conservation andanalysis with regard to the gilt bronze crown, gilt bronze sword with ring pommel with tri-leaf ornament and gilt bronze beltornaments. Bronze on the gilt bronze crown was completely corroded, therefore it was consolidated together with soil in the back of the artifact with Paraloid B72 after cleaning. Polyurethanefoams bottom was finished by applying the mixture of Epoxy resinAW106 and HV935K with soil. On the sword with ring pommel, the wooden part of the hilt was coated with Paraloid B72 (in Xylene) and the blade was consolidated with Paraloid NAD-10 30% after desalting with Sodium sesquicarbonate method. The gilt bronzebelt ornaments were treated with 3% Benzotriazole, coated with Paraloid B72 and then joined by using Cyanlacrylate. Specimens for the gilt bronze crown and gilt bronze belt ornaments were produced and gilding layers were examined under a metallographic microscope. The gilt bronze crown and the gilt bronze belt ornament maintained relatively good gilding quality with uniform gilding layers. Analysis of wood for the sheath of the sword with ring pommel revealed it to be Juglans mandshurica. Further more, analysis of constituents for a blue colored grassbead from dissolution of Polyurethane foams found it to be from the $Na_2O$-CaO-$AI_2O_3$-$SiO_2$ family.

• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.231-234
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• 2010

The effect of $C_2Cl_6$ for preventing to the surface oxidation and ignition of molten Mg alloy was studied with metallographic analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The alloy used for this study was AM100A Mg casting alloy with high strength. In order to investigate the surface protective characteristic of this molten alloy by $C_2Cl_6$ addition, we added them into molten AM100A alloy at $700^{\circ}C$ and then the melts were slowly cooled under a protective atmosphere of air containing Ar gas and $C_2Cl_6$ flux addition. The result found that the surface oxidation and ignition reaction of molten AM100A Mg alloy by adding $C_2Cl_6$ flux was more slowly occurred than that of the only a protective atmosphere of containing Ar gas with increasing time. This result was due to a dense protective film formed containing $MgCl_2$ on surface of molten Mg alloy during casting and solidification. The $MgCl_2$ was formed by a reaction of $C_2Cl_6$ with molten Mg.