• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.96-98
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• 2003

Many of research efforts have been focused on the improvement of critical current density Jc of silver-sheathed Bi-2223 tapes for practical applications of material. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking, drawing process with different heat-treatment histories. After rolling process, Bi-2223 tapes were heat-treatment at 780~826$^{\circ}C$ with variable mass flow rate of mixed gas. In this study, the effect of changes in the variable mass flow rate of mixed gas during the heat treatment of Bi-2223/Ag tapes has been investigated. Distinct differences were observed in the Bi-2223 phase and critical current as flow rate of mixed gas. We could achieve proper conditions of mass flow rate of mixed gas for Ag-alloy clad Bi-2223 superconducting tapes.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.4
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• pp.211-215
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• 2004

Conventional spheroidization process of cold heading quality steels requires long heat treatment time, and reduction of the heat treatment time is important for improving productivity in the industry. Recently, hot deformation method has been proposed as a means of increasing spherodization kinetics. In this study, the influences of hot deformation on the spherodization behavior of cold heading quality steels were investigated. Hot deformation at the temperature range of $700^{\circ}C$ significantly enhances the spheroidization kinetics. Hot deformation can lead to a substantial reduction of spherodization process time as low as 1~5 hrs.

• Journal of Ceramic Processing Research
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• v.20 no.4
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• pp.388-394
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• 2019

In this study, high-purity single-walled carbon nanotubes (SWCNTs) were prepared by removing the unreacted metal constituents and amorphous carbon impurities using a post-annealing process. Unlike conventional thermal processing techniques, this technique involved different gas atmospheres for efficient removal of impurities. A heat treatment was conducted in the presence of chlorine, oxygen, and chlorine + oxygen gases. The nanotubes demonstrated the best characteristics, when the heat treatment was conducted in the presence of a mixture of chlorine and oxygen gases. The scanning electron microscopy, transmission electron microscopy, ultraviolet absorbance, and sheet resistance measurements showed that the heat treatment process efficiently removed the unreacted metal and amorphous carbon impurities from the as-synthesized SWCNTs. The high-purity SWCNTs exhibited improved electrical conductivities. Such high-purity SWCNTs can be used in various carbon composites for improving the sensitivity of gas sensors.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.5
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• pp.76-85
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• 2013

This study was carried out to investigate the relation between surface roughness and heat absorption capability of materials for solar collector. For this purpose, 3 kinds of materials (copper, aluminum, iron), 5 kinds of surface roughness (scrubber, alumina sand #80, #200, #400, glass bead) and 2 kinds of surface treatment (black chrome plating, copper black coating) were used for finding optimal conditions to apply solar collector. As the results, it was confirmed that the optimal relations between surface roughness and surface treatment as well as optimal materials were necessary. Further, heat absorption capability was showed good results in cases of copper materials, glass bead and black chrome plating.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.1
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• pp.33-38
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• 2015

The effects of post weld heat treatment(PWHT) on the mechanical properties of 2.25Cr-1Mo steels were investigated. As the PWHT temperature or holding time increased, the strength of low alloy steels progressively decreased due to softening process. After the conventional PWHT, the strength was larger than the minimum value of materials specification. The Charpy impact energy was hardly affected by the conventional PWHT. The trend of mechanical properties was analyzed in terms of tempering parameter. Most materials replaced from a power plant met the requirements of materials specification except for one heat. Same heat of materials with low impact energy were attributed to the voids formed during casting process.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.3
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• pp.146-150
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• 2004

Because of the social needs for energy saving and the rigid environmental regulation, the development of light materials and new economical manufacturing technologies have been actively investigated. Recently, the hydroforming of high strength aluminum tube has attracted great interest due to its good strength-to-weight ratio, which could play an important role in lightweighting of automobile. However, the limited formability of high strength aluminum alloys is considered to hinder the active application of the hydroforming process. In this paper, the hydroformability of aluminum tubes with different heat treatments was investigated as the basic research of the hydroforming process for the high strength aluminum tubes.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.26-35
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• 2003

This study explains the effects of lubricant and surface treatment on hot forging die life. The mechanical and thermal load, and thermal softening which is happened by the high temperature of die, in hot and warm forging, cause die wear, heat checking and plastic deformation, etc. This study is fur the effects of solid lubricants and surface treatment condition for hot forging die. Because cooling effect and low friction are essential to the long life of dies, optimal surface treatment and lubricant are very important to improve die life for hot forging process. The main factors, which affect die hardness and heat transfer, are surface treatments and lubricants, which are related to thermal diffusion coefficient and heat transfer coefficient, etc. For verifying these effects, experiments are performed for hot ring compression test and heat transfer coefficient in various conditions as like different initial billet temperatures and different loads. The effects of lubricant and surface treatment for hot forging die life are explained by their thermal characteristics. The new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.2
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• pp.83-89
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• 2010

Diamond-like carbon (DLC) coating was studied to be a good tribological problem-solver due to its low friction characteristics and high hardness. However, generally hydrogenated DLC film has shown a weak thermal stability above $300^{\circ}C$. However, the silicon doping DLC process by DC pulse plasma enhanced chemical vapor deposition (PECVD) for the new DLC coating which has a good characterization with thermal stability at high temperature itself has been observed. And we were discussed a process for optimizing silicon content to promote a good thermal stability using various tetramethylsilane (TMS) and methane gas at high-temperature. The chemical compositions of silicon-containing DLC film was analyzed using X-ray photoelectron spectroscopy (XPS) before and after heat treatment. Raman spectrum analysis showed the changed structure on the surface after the high-temperature exposure testing. In particular, the hardness of silicon-containing DLC film showed different values before and after the annealing treatment.

• Korean Journal of Metals and Materials
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• v.47 no.8
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• pp.482-487
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• 2009

In order to investigate the effects of intermediate heat treatment between cold rolling passes on the hardness and corrosion properties of a Zr alloy incorporating Nb (Zr-1.49Nb-0.38Sn-0.20Fe-0.11Cr) strip, three different intermediate heat treatment processes ($580^{\circ}C{\times}4hrs$, $600^{\circ}C{\times}2hrs$ and $620^{\circ}{\times}1hrs$) were designed based on a recrystallization map and an accumulated annealing parameter. Test samples from the different processes were investigated by a hardness test, corrosion test, and microstructure analysis and appropriate heat-treatment conditions were thereupon proposed. The sample subjected to an intermediate heat treatment of $580^{\circ}C{\times}4hrs$ was harder than that undergoing $600^{\circ}C{\times}2hrs$ and $620^{\circ}C{\times}1hr$ while the corrosion resistance of the sample that received an intermediate heat treatment of $580^{\circ}C{\times}4hrs$ was superior to that of the other specimens. Considering the trade-off of hardness and corrosion resistance, an intermediate heat treatment process of $600^{\circ}C{\times}2hrs$ is proposed to improve the manufacturing process of the alloy strip.

• Journal of the Korean Ceramic Society
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• v.28 no.6
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• pp.488-494
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• 1991

In this study, the effects of catalyst and DCCA content were investigated in order to determine the optimum conditions of monolithic silica gel formation through sol-gel process. Formamide, oxalic acid, glycerol and dimethylformamide are used as DCCA. To observe the phenomena in drying and heat-treating of gels, we examined structural exchange of gels using FT-IR, TG-DTA and XRD. Monolithic gels were obtained by adding formamide and dimethylformamide as DCCA. According to the heat treatment schedule, silica glass is prepared by heat-treatment up to 1050$^{\circ}C$.