• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.117.2-117.2
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• 2005

• Nuclear Engineering and Technology
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• 제40권3호
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• pp.233-238
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• 2008

This study investigates the surface modification of a Hastelloy X plate and diffusion bonding in the assembly of surface modified plates. These types of plates are involved in the key processes in the fabrication of a process heat exchanger (PHE) for a $SO_3$ decomposer. Strong adhesion of a SiC film deposited onto Hastelloy X can be achieved by a thin SiC film deposition and a subsequent N ion beam bombardment followed by an additional deposition of a thicker film that prevents the Hastelloy X surface from becoming exposed to a corrosive environment through the pores. This process not only produces higher corrosion resistance as proved by electrolytic etching but also exhibits higher endurance against thermal stress above 9$900^{\circ}C$. A process for a good bonding between Hastelloy X sheets, which is essential for a good heat exchanger, was developed by diffusion bonding. The diffusion bonding was done by mechanically clamping the sheets under a heat treatment at $900^{\circ}C$. When the clamping jig consisted of materials with a thermal expansion coefficient that was equal to or less than that of the Hastelloy X, sound bonding was achieved.

• 한국주조공학회지
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• 제37권5호
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• pp.139-147
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• 2017

Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

• 한국결정성장학회지
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• 제22권4호
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• pp.183-189
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• 2012

고온 열수송용 재료로 이용되는 Hastelloy X의 표면처리에 따른 고온물성 개선에 대한 연구를 수행하였다. Hastelloy X 기판 상에 각각 PVD법인 Arc discharge 및 Sputtering을 이용하여 TiAlN 및 $Al_2O_3$ 박막을 표면 코팅(overlay coating) 하였고, 분위기 분말을 이용하여 Al을 금속표면을 통해 확산시키는 방법인 Pack cementation법을 이용한 Al 확산코팅(diffusion coating: aluminiding)법을 이용한 표면처리를 수행하였다. 이들 표면처리가 Ni-Cr계 합금의 고온열처리에서 생성되는 두꺼운 불균질 산화물($Cr_2O_3$)형성 억제에 미치는 효과와 조성 및 표면미세구조가 물성에 미치는 영향에 대해 알아보기 위해, 표면처리 된 Hastelloy X 샘플들을 공기 및 헬륨가스 분위기에서 $1000^{\circ}C$로 열처리 하였으며, 열처리된 전후 시편들에 대해 상형성, 미세구조 및 고온 물성 변화를 측정하였다. 이러한 실험결과를 통하여 표면코팅법에 의한 TiAlN 및 $Al_2O_3$ 박막에 비해 Al 확산코팅한 경우 두꺼운 불균질 산화물($Cr_2O_3$)형성이 억제되어 보다 균질한 미세구조와 높은 내마모성 등 높은 고온 안정성을 보여주는 것을 확인할 수 있었다.

• 소성∙가공
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• 제31권3호
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• pp.136-142
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• 2022

The purpose of this study was to investigate the effects of sample thickness and support structure on the residual stress of Hastelloy X superalloy samples fabricated by laser powder bed fusion (LPBF), which is an additive manufacturing process. The residual stresses of LPBF samples with different thicknesses and support structures were measured using X-ray diffraction. The results revealed that as the thickness of sample increased from 2.5 mm to 20 mm, its tensile residual stress gradually decreased from 443.5 MPa to 182.2 MPa. Additionally, the residual stress in the bottom region of sample was higher than that in the top region, and the residual stress difference in the bottom and top regions became more pronounced as the sample thickness decreased. The residual stress of LPBF sample also varied depending on the structure of support. The residual stress of sample decreased with increasing contract area between the sample and the support, because the larger contract area led to smaller temperature gradient throughout the sample.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2005년도 춘계학술발표대회 및 제8회 신소재 심포지엄 논문개요집
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• pp.266-266
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• 2005

• 한국재료학회지
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• 제16권5호
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• pp.318-322
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• 2006

Short-term high temperature degradation test was conducted on Hastelloy X, a candidate tube material for high temperature gas-cooled reactors (HTGR), to evaluate the variation of microstructure and mechanical property in air at $1050^{\circ}C$ during 2000 h. The dominant oxide layer was Cr-oxide and a very shallow Cr-depleted region was observed below the oxide layer. At the beginning of degradation, the island shape $M_6C$ precipitate (M=Mo-rich, Fe, Ni, Cr) was observed in matrix region. After 2000 h degradation, precipitate shape was changed to the chain shape and increased amount of precipitate. These results influenced mechanical property of the specimen which exposed in high temperature. Yield strength was decreased from 115MPa to 89 MPa after 24 h and 2000 h exposure, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.205.2-205.2
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• 2014

The effects of ion beam mixing of a SiC film coated on super alloys (hastelloy X substrates) were studied, aiming at developing highly sustainable materials at above $900^{\circ}C$ in decomposed sulfuric acid gas (SO2/SO3/H2O) channels of a process heat exchanger. The bonding between two dissimilar materials is often problematic, particularly in coating metals with a ceramics protective layer. A strong bonding between SiC and hastelloy X was achieved by mixing the atoms at the interface by an ion-beam: The film was not peeled-off at ${\geq}900^{\circ}C$, confirming excellent adhesion, although the thermal expansion coefficient of hastelloy X is about three times higher than that of SiC. Instead, the SiC film was cracked along the grain boundary of the substrate at above $700^{\circ}C$. At ${\geq}900^{\circ}C$, the film was crystallized forming islands on the substrate so that a considerable part of the substrate surface could be exposed to the corrosive environment. To cover the exposed areas and cracks multiple coating/IBM processes have been developed. An immersion corrosion test in 80% sulfuric acid at $300^{\circ}C$ for 100 h showed that the weight retain rate was gradually increased when increasing the processing time.

• 에너지공학
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• 제10권2호
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• pp.132-139
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• 2001

석탄가스화 복합발전의 집진 공정에 사용하기 위한 금속제 safety filter의 재질 선정을 위하여 황화수소 가스 분위기에서 합금강의 부식 특성을 규명하였다. 사용 합금강은 SUS 310, SUS 316, Inconel 600과 Hastelloy X이다. 전기로 내에 설치된 지름 50mm의 qualtz 튜브 반응기에서 부식실험이 행하여졌다. 40$0^{\circ}C$부터 $700^{\circ}C$까지의 등은 조건에서 실험이 행하여졌고, 분위기 가스의 영향을 보기 위하여 H$_2$S 가스를 함유한 $N_2$(dry), $N_2$(saturation), $CO_2$(dry), 그리고 석탄가스 분위기에서 실험하였다. 부식 생성물을 파악하기 위하여 X-ray 회절기와 주사전자현미경 분석이 함께 이루어졌다. 1.7% H$_2$S, $600^{\circ}C$ 이하 온도 조건에서는 니켈계 내식강 중 Hastelloy X와 철계 내식강 중 SUS 310 등 고크롬 합금강이 IGCC 용 필터 소재 금속으로서 높은 내부식성을 나타내었다. 0.3%~4.99% 황화수소 농도 범위에서 황화수소 농도 변화에 따라서 SUS 310의 경우 3~237mg/d$m^2$.day, Inconel 600의 경우 4~660mg/d$m^2$.day로 부식속도는 크게 증가되었다. 50$0^{\circ}C$, 석탄가스 분위기에서 부식속도는 SUS 310은 45mg/d$m^2$.day, SUS 316은 110mg/d$m^2$.day, Inconel 600은 576mg/d$m^2$.day, 그리고 Hastelloy X 는 140mg/d$m^2$.day로서 합금강 시편 중 SUS 310 합금강이 가장 우수한 내식성을 나타내었다. 부식 표면에는 황화니켈, 황화철 피막이 형성되었다.

• 한국기계가공학회지
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• 제20권10호
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• pp.27-37
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• 2021

The use of additive manufacturing processes for the repair and remanufacturing of mechanical parts has attracted considerable attention because of strict environmental regulations. Directed energy deposition (DED) is widely used to retrofit mechanical parts. In this study, finite element analyses (FEAs) were performed to investigate the influence of the substrate phase and inclination angle on the heat transfer characteristics in the vicinity of Hastelloy X regions deposited via DED. FE models that consider the bead size and hatch distance were designed. A volumetric heat source model with a Gaussian distribution in a plane was adopted as the heat flux model for DED. The substrate and the deposited powder were S45C structural steel and Hastelloy X, respectively. Temperature-dependent thermal properties were considered while performing the FEAs. The effects of the substrate phase and inclination angle on the temperature distributions and depth of the heat-affected zone (HAZ) in the vicinity of the deposited regions were examined. Furthermore, the influence of deposition paths on depths of the HAZ were investigated. The results of the analyses were used to determine the suitable phase and inclination angle of the substrate as well as the appropriate deposition path.