• Journal of Welding and Joining
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• v.31 no.3
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• pp.76-83
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• 2013

This study investigated the effect of bonding temperature and holding time on microstructures and mechanical properties of diffusion bonded joint of Haynes230. The diffusion bonds were performed at the temperature of 950, 1050, and $1150^{\circ}C$ for holding times of 30, 60, 120 and 240 minutes at a pressure of 4MPa under high vacuum condition. The amount of non-bonded area and void observed in the bonded interface decreased with increasing bonding temperature and holding time. Cr-rich precipitates at the linear interface region restrained grain migration at $950^{\circ}C$ and $1050^{\circ}C$. However, the grain migration was observed in spite of short holding time due to the dissolution of precipitates to base metal in the interface region at $1150^{\circ}C$. Three types of the fracture surface were observed after tensile test. The region where the coalesce and migration of grain occurred much showed high fracture load because of base metal fracture whereas the region where those did less due to the precipitates demonstrated low fracture load because of interface fracture. The expected fracture load could be derived with the value of fracture area of base metal ($A_{BF}$) and interface ($A_{IF}$), $Load=201A_{BF}+153A_{IF}$. Based on this equation, strength of base metal and interface fracture were calculated as 201MPa and 153MPa, respectively.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.2
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• pp.26-33
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• 2011

To evaluate steam oxidation behaviours of Alloy 617 and Haynes 230, oxidation test were performed at $900^{\circ}C$ in steam and $steam+20\;vol.-%\;H_2$ environments. Oxidation rate in steam condition was similar to that in air for Alloy 617, while it was slightly lower for Haynes 230. When hydrogen was added to steam, oxidation rate was enhanced. Isolated $MnTiO_3$ particle were formed on $Cr_2O_3$ oxide layer and sub layer $Cr_2O_3$ were formed in steam and $steam+20\;vol.-%\;H_2$ for Alloy 617. On the other hands, $MnCr_2O_3$ layer were formed on top of $Cr_2O_3$ oxide layer for Haynes 230. The extensive sub layer $Cr_2O_3$ formation was resulted from the oxygen inward diffusion in such environments. When hydrogen was added, the oxide morphology was changed from polygonal to platelet because of the accelerated diffusion of cations under the oxide layer. In addition, decarburized zone was extended as hydrogen participated into the reactions causing carbide dissolution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.177-183
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• 2005

In this work, Inconel 600, Inconel 625 and Haynes 230 are welding using Nd:YAG laser and electron bear. These heat-resistant alloys are typically used for the liquid thruster. To examine, the affects of experimental parameters on weld ability, the plate welding of these materials were carried out using both Nd:YAG laser and electron bear. Also, the micro-structure, micro-hardness, and tensile strength of the specimens were analyzed. from the analysis of the experimental results of laser and electron beam welding, we have obtained the optimal welding conditions.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.158-160
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• 2006

Super alloys are typically used for the liquid thruster in the aerospace industry. In this work, The bead-on-plate welding of Inconel 600, Inconel 625 and Haynes 230 using Nd:YAG laser are studied, in order to examine the effects of experimental parameters on their weldability. The micro-hardness and tensile strength of the specimens are also analyzed, to obtain the optimal welding conditions.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.195-197
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• 2005

An intermediate heat exchanger(IHX) is a key component in a next-generation VHTR with process heat applications such as hydrogen production and also for an indirect gas turbine system. Therefore, high temperature brazing with nickel-based filler metal(MBF-15) was carried out to study the joining characteristic(microstucture, joining strength) of nickel-based superalloy(Haynes 230) by vacuum brazing. The experimental brazing was carried out at the brazing process, an applied pressure of about 0.74Mpa and the three kinds of brazing temperatures were 1100, 1150, and $1190^{\circ}C$ with holding time 5 minute. It's joining phenomena were analyzed by optical microscopy and scanning electron microscopy with EPMA. The results of microstructure in the centre-line region of a joint brazed with MBF-15 show a typical ternary eutectic of v-nickel, nickel boride and chromium boride.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.1-7
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• 2011

Methods of producing hydrogen include steam reforming, electrochemical decomposition of water, and the SI process. Among these methods, the Sulfur iodine process is one of the most promising processes for hydrogen production. The thermochemical sulfur-iodine (SI) process uses heat from a high-temperature-gas nuclear reactor to produce $H_2$ gas; this process is known for its production of clean energy as it does not emit $CO_2$ from water. But the SI-process takes place in an extremely corrosive environment for the materials. To endure SI environments, the materials for the SI environment will have to have strong corrosion resistance. This work studies the corrosion resistances of the Fe-Si, Ni-Ti and Ni Alloys, which are tested in SI-process environments. Among the SI-process environments, the conditions of boiling sulfuric acid and decomposed sulfuric acid are selected in this study. Before testing in boiling sulfuric acid environments, the specimens of Fe-4.5Si, Fe-6Si, Ni-4.5Si, Ni-Ti-Si-Nb and Ni-Ti-Si-Nb-B are previously given heat treatment at $1000^{\circ}C$ for 48 hrs. The reason for this heat treatment is that those specimens have a passive film on the surface. The specimens are immersed for 3~14 days in 98wt% boiling sulfuric acid. Corrosion rates are measured by using the weight change after immersion. The corrosion rates of the Fe-6Si and Ni-Ti-Si-Nb-B are found to decrease as the time passes. The corrosion rates of Fe-6si and Ni-Ti-Si-Nb-B are measured at 0.056 mm/yr and 0.16 mm/yr, respectively. Hastelloy-X, Alloy 617, Alloy 800H and Haynes 230 are tested in the decomposed sulfuric acid for one day. Alloy 800H was found to show the best corrosion resistance among the materials. The corrosion rate of Alloy 800H is measured at -0.35 mm/yr. In these results, the corrosion resistance of materials depends on the stability of the oxide film formed on the surface. After testing in boiling sulfuric acid and in decomposed sulfuric acid environments, the surfaces and compositions of specimens are analyzed by SEM and EDX.