• Journal of Korea Foundry Society
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• v.32 no.3
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• pp.150-156
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• 2012

발포금속은 초경량 재료로서 폐기공과 개기공의 두 가지 형태의 구조를 지니고 있으며 폐기공은 내충격성, 흡음성, 단열성의 기능을 지니고 있고, 개기공은 필터, 생체지지대, 촉매재, 열방출재 등으로 사용되고 있다. 개기공발포재는 삼차원 구조모양으로 프리커서를 이용한 압력정밀주조나 기공입자용출법으로 제조하고 있으나 기공의 크기나 셀의 형상, 두께 등을 조절하기에 어려움이 있다. 이를 해결하기 위하여 환경친화적인 펄라이트를 사용하여 목적하는 크기의 그래뉼을 제조한 후, 용융마그네슘합금을 감압주조법으로 주조하여 그래뉼의 크기로 기공율을 조절하고, 주형의 온도와 압력에 따른 유동의 길이를 측정하였다. 그래뉼 직경이 2.3 $mm{\O}$ 일때에 주형의 온도 $300^{\circ}C$ 이상, 압력이 5000 Pa 이상에서 유동길이 6.5 cm 이상을 얻었다.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.171-178
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• 2023

For the phase boundary crack found in the gasket made of cast austenitic stainless steel in the nuclear power plant, the oxide layers were analyzed through SEM and TEM. The results showed that cracks initiated and propagated along the austenite/δ-ferrite phase boundary, the propagation path was changed to penetrate the inside of the phase. The oxide layer located at the periphery of the crack along the phase boundary was identified as a complex multi-layered spinel structure, and Cr-rich carbides were also detected in the oxide. The cracks that propagated inside the austenite matrix were attributed to the presence of high external stresses and impurities.

• Journal of Korea Foundry Society
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• v.3 no.1
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• pp.28-36
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• 1983

In order to study the cast structure and mechanical properties of Al-10 % Mg alloy solidified under the various high hydraulic pressure, ranging from $0kgf/cm^2$ to $2000㎏f/cm^2$ , the relationship between the cooling rate and the cast structure was observed, and also the mechanical test and the measurement of the specific gravity were carried out. From this experiment, results were summerized as follows; 1. The cooling rate of the alloy increased with increase of the applied pressure. 2. The formation of the piping and the porosity in the castings was surpressed by applying the high hydraulic pressure. 3. The dendrite arm spacing decreased with increase of the applied pressure. 4. Mechanical properties and specific gravity increased with the increase of the applied pressure.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.302-309
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• 2023

In general, castings often have complex shapes and significant variations in thickness within a single product, making grid generation for simulations challenging. Casting flows involve multiphase flows, requiring the tracking of the boundary between air and molten metal. Additionally, considerable time is spent calculating pressure fields due to density differences in a numerical analysis. For these reasons, the Cartesian grid system has traditionally been used in mold filling simulations. However, orthogonal grids fail to represent shapes accurately, leading to a momentum loss caused by the stair-like grid patterns on curved and sloped surfaces. This can alter the flow of molten metals and result in incorrect casting process designs. To address this issue, simulations in the Cartesian grid system involve creating a large number of grids to represent shapes more accurately. Alternatively, the Cut Cell method can be applied to address the problems arising from the Cartesian grid system. In this study, analysis results based on the number of grid in the Cartesian grid system for a casting flow analysis were compared with results obtained using the Cut Cell method. Casting flow simulations of actual products during various casting processes were also conducted, and these results were analyzed with and without applying the Cut Cell method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.805-810
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• 2006

Defects in the conventional casting process of silver jewelry can result in famished products of mediocre hardness. To overcome the shortcomings of conventional methods, we proposed new press forming process, which involves applying uniaxial pressure on casting 92.5%Ag-6.5%Cu-1%Zn ring elements and shaping with a lath. We investigated Vickers hardness, density, and microstructure evolution by changing the applied uniaxial pressure. We report that our newly proposed process can increase the hardness up to 2.3 times and decrease average grain size by 50%. Our method leads to drastic mechanical property enhancements, and is thus suitable for casting tension-style jewelry.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.16-22
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• 2010

Cast austenitic stainless steel(CASS) is used in the primary cooling piping system of nuclear power plant for it's relative low cost, corrosion resistance and easy of welding. However, the coarse-grain structure of cast austenitic stainless steel can strongly affect the inspectability of ultrasonic testing. The major problems encountered during inspection are beam skewing, high attenuation and high background noise of CASS component. So far, the best inspection performance involving CASS components have been achieved using low frequency TRL(Transmitter/Receiver side-by-side L wave) angle beam probe. But TRL technique could not detect shallow defect and it contains an uncertainty for sizing capability. Currently, most of researchers are studying to overcome these challenge issue. In this study, low-frequency phased array TRL technique used to detect and sizing the flaws in CF8A cast austenitic stainless steel.As conclusion, we could detect and size not only axial flaw but also circumferential flaw using low frequency phased array technique.

• Journal of Korea Foundry Society
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• v.23 no.3
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• pp.147-152
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• 2003

질소 용해도가 낮은 ${\delta}$상으로 응고가 시작되는 16Cr-3Ni 계 스테인리스강의 응고시 질소기포 형성에 미치는 질소 함량과 냉각속도의 영향이 조사되었으며 이를 기반으로 질소 기포 결함이 발생하는 임계 질소 함량을 예측하는 방법을 제시하였다. 질소함량의 증가는 질소 기포 결함을 증가시켰으며, 냉각속도의 증가는 질소기포결함의 형성을 다소 억제 할 수 있는 것으로 조사되었다. 실험적으로 구한 Fe-16Cr-3Ni-9Mn 합금의 임계 질소 함량은 0.19wt%였으며, 임계 질소 압력은 평형응고로 가정한 경우 1.27atm, Scheil 응고로 가정한 경우에는 1.23atm으로 계산되었다. 질소 용해도를 증가시킬 수 있는 Mn 함량의 변화에 따른 임계 질소 함량의 변화를 예측하기 위하여 계산된 임계 질소 압력을 Fe-16Cr-3Ni-11Mn 합금에 적용하였으며 이를 통해 얻은 임계 질소 함량은 평형응고로 가정한 경우 0.25wt%, Scheil 응고로 가정한 경우에는 0.24wt% 로 예측되었다. 예측 결과의 타당성을 확인하기 위하여 Fe-16Cr-3Ni-11Mn 합금의 실험 결과와 비교하였으며, 일치하는 결과가 얻어졌다.

• Journal of Korea Foundry Society
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• v.24 no.1
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• pp.26-33
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• 2004

The pressure of the mold flux acting on the meniscus shell was investigated through the coupling analysis of heat transfer in the mold and fluid flow in the flux caused by the mold oscillation. Finite element method was employed to solve the conservation equation associated with appropriate boundary conditions. As reported by previous workers, the axial pressure is positive on the negative strip time and negative on the positive strip time. A maximum pressure is predicted toward the top of the meniscus shell which has the thin shell arid a maximum value is in proportion to the relative mold oscillation velocity. The relative mold oscillation velocity was changed by the effect of meniscus level fluctuation. Therefore the pressure of the mold flux acting on the meniscus shell was different each cycle of the mold oscillation due to the irregularity of relative mold oscillation velocity.

• Journal of Korea Foundry Society
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• v.20 no.4
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• pp.247-253
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• 2000

Titanium was melted in the CaO-coated alumina crucible and the reaction between the melt and the coating layer was negligible. The volume fraction of the gas porosity was decreased with increasing pressure and the sound bar castings with no porosity was obtained under the Ar atmosphere of the pressure of $300kN/mm^2$. The surface of the casting obtained from CaO-coated graphite mold was slightly rougher than that from graphite without coating. The reaction product of titanium melt with the layer of CaO was mainly titanium oxide and that with graphite crucible was titanium cabide with small amount of titanium nitride.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.56-65
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• 2024

Cast austenitic stainless steels (CASS) and austenitic stainless steel weldments with a ferrite-austenite duplex structure are widely used in nuclear power plants, incorporating ferrite phase to enhance strength, stress relief, and corrosion resistance. Thermal aging at 290-325℃ can induce embrittlement, primarily due to spinodal decomposition and G-phase precipitation in the ferrite phase. This study evaluates the effects of thermal aging by collecting and analyzing various mechanical properties, such as Charpy impact energy, ferrite microhardness, and tensile strength, from various literature sources. Different model expressions, including hyperbolic tangent and phase transformation equations, are applied to calculate activation energy (Q) of room-temperature impact energies, and the results are compared. Additionally, predictive models for Q based on material composition are evaluated, and the potential of machine learning techniques for improving prediction accuracy is explored. The study also examines the use of ferrite microhardness and tensile strength in calculating Q and assessing thermal embrittlement. The findings provide insights for developing advanced prediction models for the thermal embrittlement behavior of CASS and the weldments of austenitic steels, contributing to the safety and reliability of nuclear power plant components.