• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.06a
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• pp.135-147
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• 1997

The production of light metal parts using aluminum is mainly performed by die casting and squeeze casting, which directly fabricate the required shape from the liquid state. However, die casting is subject to defects such as shrinkage porosity and air trapped when molten metal enters the cavity, whilst squeeze casting also has defects due to turbulent flow in the die cavity. Both diecasting and sqeeze casting have inhomogeneous mechanical property in terms of dendritic structure during solidification. Active research has been carried out on semi-solid processing, rather than on conventional process methods such as die casting, which involve various problems. Therefore in this paper, to introduce the fundamental technology for d e design, in die casting and forging process with semi-solid materials, relationship between stress and strain of semi-solid materials, and for producing parts die design has been proposed as parameters of globulization of the microstructure and gate shape. The prevention of various defects to produce sound parts are also introduced.

• Journal of Korea Foundry Society
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• v.37 no.1
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• pp.21-29
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• 2017

The effects of W content and heat treatment on the microstructure and mechanical properties of Hastelloy C-276 alloy investment castings were discussed. As the W content was increased, dendritic microstructure was refined and network type precipitate formed during solidification was distributed on the dendritic grain boundaries. Cr, Fe and Mn were highly segregated in the Ni-based dendrite matrix, and Mo, W, C and Si were in the precipitates. Due to the heat treatment, fine granular and flake precipitates were newly formed in the matrix, and unresolved network type precipitates remained on the grain boundary. The network type precipitates and the granular and flake precipitates formed by heat treatment were confirmed to be ${\mu}$ phase intermetallic compounds with similar compositions. Due to the increase of the W content and the heat treatment, hardness and tensile strength were significantly increased. However, tensile strength after aging treatment was decreased with the W content. These results can be explained in that brittle fracturing by the unresolved network type precipitates dispersed in the grain boundary was predominant over ductile fracturing by the dimple ruptures originating from the fine granular precipitates in the matrix.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.37-43
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• 2015

Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of ${\delta}$-ferrite was increased with increasing heat input due to the increase of Creq/Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.

• Fire Science and Engineering
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• v.31 no.6
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• pp.83-90
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• 2017

If an overcurrent exceeding the rated value is applied to an electric wire, the temperature of the electric wire increases, and the electric wire covering deteriorates to cause a short circuit. The upper limit temperature of the wire varies according to the magnitude of the overcurrent. When a short circuit occurs at each upper temperature limit, a cooling speed difference occurs during the solidification process due to the temperature difference between the short circuit temperature and the wire surface temperature. At this time, the pattern characteristics of the dendritic structure formed on the molten cross section are different. In this study, the upper temperature limit, which varied according to the overcurrent magnitude, was measured. At the time a short circuit occurred, the second branch spacing (dendrite Arm Spacing : DAS) of the dendrite was analyzed and the numerical value was quantified. The experimental results showed that the upper temperature limit increases with the magnitude of the overcurrent, and that the second branch spacing increases with increasing wire temperature.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.49-59
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• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• Journal of Powder Materials
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• v.22 no.5
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• pp.362-366
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• 2015

The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at $-25^{\circ}C$. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at $300^{\circ}C$ and sintering at $850^{\circ}C$ for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.

• Journal of Korea Foundry Society
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• v.31 no.6
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• pp.354-361
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• 2011

The liquid metal shearing device was constructed and assembled with a commercial high-pressure die-caster in order to induce intensive turbulent shearing force on molten aluminum alloys. The effect of the liquid metal shearing on the microstructure and tensile properties of A356 alloys was investigated with the variation of iron content. The experimental results show that dendritic primary ${\alpha}$-Al phase was effectively modified into a equiaxed form by the liquid metal shearing. It was also found that the needle-like ${\beta}$-AlFeSi phase in a Fe containing A356 alloy was changed into a blocky shape resulting in the improved mechanical properties. Based on the mechanical properties, it was suggested that the iron content in A356 alloy could be more widely tolerated by utilizing the liquid metal shearing HPDC process.

• Advances in materials Research
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• v.7 no.1
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• pp.17-28
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• 2018

Niobium is a candidate base for new alloys devoted to applications at especially elevated temperatures. Elaborating and shaping niobium-based alloys by conventional foundry may lead to mechanically interesting microstructures. In this work a series of charges constituted of pure elements were subjected to high frequency induction melting in cold crucible to try obtaining cast highly refractory Nb-xCr and Nb-xCr-0.4 wt.%Calloys(x=27, 34 and 37 wt.%). Melting and solidification were successfully achieved. The as-cast microstructures of the obtained alloys were characterized by electron microscopy and X-ray diffraction and their hardness were specified by Vickers macro-indentation. The obtained as-cast microstructures are composed of a body centered cubic (bcc) niobium dendritic matrix and of an interdendritic eutectic compound involving the bcc Nb phase and a $NbCr_2$ Laves phase. The obtained alloys are hard to cut and particularly brittle at room temperature. Hardness is of a high level (higher than 600Hv) and is directly driven by the chromium content or the amount of {bcc Nb - $NbCr_2$} eutectic compound. Adding 0.4 wt.% of carbon did not lead to carbides but tends to increase hardness.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.435-443
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• 1990

By using the centrifugal atomization, which is one of the rapid solidification processes, Al-5,10wt%Pb alloys which are monotectic alloys were melted at 150K over two liquid phase line in the phase diagram. The melted alloy was poured on the rotating disk, being made into atomized powders, and then the solidified microstructure and morphology of the powder were investigated. This study converted the produced powders into strips by strained powder rolling. According to sintering temperature, the microstructure and hardness were investigated. The solidified structure of the powders were almost cellular dendritic structure. Pb particles ($2.0-3.0{\mu}m$) were fairl distributed in the Al matrix. Powder shapes were irregular. Rolling property and the compacting was good, respectively, because of increasing mechanical interlocking and surface area in the small size powders. With increasing temperature, the boundarys of powders were in porous form due to the diffusion. Pb particles which were surrounding the pores were inverse-segregated at the surface of the powders. With increasing of sintering temperature, the hardness of the powders and the strips decreased. In particular rolling-strip, the hardness abruptly decreased due to the release of work-hardening.

• Journal of Korea Foundry Society
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• v.30 no.4
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• pp.130-136
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• 2010

Sulfide segregation behavior, characteristics of solidification microstructure and compositional distribution in the riser/castings junction of heavy-section main bearing support (MBS) steel castings were investigated; Sulfide streaks of A segregation were formed in the transitional region from columnar grain to coarse equiaxed grain and floated with aggregation of the dendritic free crystal. Solute segregation behaviors of elements Si, P and S were V shape negative segregation from the bottom of the castings to upper part of the riser with the reference of vertical center-line of the specimen block. Those of elements C and Mn were V shape negative segregation in the main body and A shape positive segregation in the riser of the casting. Just beneath the pipe shrinkage in the riser segregation ratio of each element was the highest, and that of S was 3.6 times higher, C 3.3 times, P 2.1 times, Si 1.6 times and Mn 1.0 times respectively. [Mn/S] ratio of the specimen block was distributed in the wide range of 20~275.