• Transactions of the Korean hydrogen and new energy society
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• v.17 no.1
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• pp.109-116
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• 2006

The heat treatment characteristics of natural talc sample was investigated in diverse analytical view point. The mass decrease comes to heat treatment was resulted by the continuous and the discontinuous process and the obtained result show very similar two step profiles with 8.9 % mass decrease. The dehydroxylation of -OH groups contained talc crystal was analyzed by spectroscopic method and the crystallographic variations was also observed after heat treatment. According to XPS result, the magnesium hydroxide($Mg(OH)_2$) of untreated talc powder changed to magnesium oxides(MgO) after heat treatment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.260-263
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• 2004

Since Outerrace is one of the components of driving shaft for power train of automobile and transmits high torque, high strength and high toughness are necessary so forging process is adopted to manufacture such parts. Therefore, in order to improve strength and toughness, heat treatment is accomplished after plastic deformation(forging). Because Each component of driving shaft is mounted to automobile after a series of forging, machining and heat treatment, in order to evaluate mechanical properties of such components in use, plastic deformation and heat treatment must be considered. So, in this paper, tensile tests are performed with tensile specimens which have passed through a series of upsetting, machining and heat treatment to evaluate mechanical properties of such components.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.62-68
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• 1996

In order to establish making process of water atomized iron powder for powder metallurgy, effect of heat treatment condition on change of powder properties and impurities was investigated at each tempeature of $850{\sim}950^{\circ}C$. The results are as follows. Particle morphology of iron powder changed slightly from sphercial type to irregular type and the amount of fine particle decreased more and more with increasing of heat treatment time at each temperature. The flow rate and apparent desity of iron powder also decreased due to particle coalescence in order of $850^{\circ}C$, $950^{\circ}C$, $900^{\circ}C$. Those powder Properties became to decrease particularly at $900^{\circ}C$ in alpha iron region. On the other hand, residual carbon and oxygen contents in iron powder decreased extremely with increasing of heat treatment temperature and time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.225-228
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• 1997

The main fault in this interface is that power cable insulating materials are mainly composed of a double layered structure, XLPE/FPDM laminates in cable joint. In this parer, we instituted the interface of XLPE/EPDM laminates and then investigated the breakdown and conduction characteristics as a function of heat treatment time. The results showed that conduction current was influenced by volatile crosslinking by-products which remained inside the insulating material during the production of XLPE and EPDM, especially during heat treatment process. And conduction current of XLPE/Oil 12500cSt/EPDM was more stable than XLPE/Grease/EPDM from the long heat treatment time. AC breakdown strength of silicone oil itself from the heat treatment was changed during the 4∼12 hour heat treatment time.

• Journal of Korea Foundry Society
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• v.20 no.3
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• pp.173-180
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• 2000

The microstructure changes of the matrix and the graphites were observed by optical microscope and the average hardness number was investigated according to the heat-treatment conditions of the cast iron rods by the horizontal continuous casting process in 35 mm diameter. The three kinds of heat-treatments were introduced. The first treatment was performed at 900, 950, and $1000^{\circ}C$ for 2 hours and the second treatment was conducted during 5, 10, and 15 hours at $1000^{\circ}C$ respectively. The third treatments were the two-cyclic heat-treatment and the three-cyclic heat-treatment at $1000^{\circ}C$ during 2 hours. The matrix microstructure of the specimens to be treated at various temperatures for 2 hours was the ferrite to be transformed from the pearlite The hardness number of the center of the samples according to the heat treatment time at $1000^{\circ}C$ was higher than that of the surface area because of the martensite formation in the center. Also, in the cyclic heat-treatments, the hardness number of the two-cycle treatment specimens increased because of the martensite formation in the center.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.3
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• pp.121-127
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• 2023

When high carbon steel is heated in an appropriate austenizing temperature range and subjected to austempering, the size and shape of lamellar structure can be controlled. The high carbon steel sheet having the pearlite structure has excellent elastic characteristics because it has strong restoring force when properly rolled, and is applied in a process known as patenting-process using lead bath. In the case of isothermal treatment using lead-medium, it is possible to quickly reach a uniform temperature due to high heat transfer characteristics, but it is difficult to replace it with process technology that requires treatment to remove harmfulness lead. In this study, we intend to develop fluidization technology using garnet powder to replace the lead medium. After heating the high-carbon steel, the cooling rate was changed by compressed air to the vicinity of the nose of the continuous cooling curve, and then maintained for 90 s and then exposed to room temperature. The microstructure of the treated specimens were analyzed and compared with the existing products treated with lead bath. The higher the flow rate of compressed air, the faster the cooling rate to the pearlite transformation temperature, so lamellar spacing decreases and the hardness tends to increase.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.5
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• pp.63-68
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• 2010

The use of aluminum alloy parts in the automotive industry has been increasing recently due to its low weight compared with steel to improve fuel efficiency. Companies in the auto parts' manufacturing sector are expected to meet the government's strict environmental regulations. In this study, manufacturing process of aluminum alloy bolt has been designed from forming to heat treatment. Bolt forming process is composed of cold forging for body and rolling for thread. In this study only cold forging process is considered by employing the finite element method. In the cold forging process, preform shape was designed and damage value was considered for die design. Two steps of forging process has been developed by the simulation and a prototype was manugactured accordingly. As a final process, solution heat treatment and aging process was employed. A final prototype was found to meet the required specifications of tensile strength and dimension.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.1
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• pp.17-23
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• 2015

Hydroxyapatite coatings were fabricated by a room temperature spray method on zirconia substrates and the influence of heat-treatment on their microstructure was also investigated. Phase composition of coated hydroxyapatite films was similar to the starting powder, but the grain size of hydroxyapatite particles was reduced to the size of nano-scale about 100 nm. Grain size, particle compactness, and adhesiveness to zirconia of hydroxyapatite coatings were increased with heat-treatment temperature, but some of cracks by heat-treatment above $1100^{\circ}C$ were initiated between hydroxyapatite coatings and zirconia substrate. Heat-treated hydroxyapatite layers show the dissolution in SBF solution for 5 days. Hydroxyapatite-coated specimen heat-treated at $1100^{\circ}C$ for 1 h has a good biocompatibility, which specimen induced the nanocrystalline hydroxyapatite precipitates on the coating surface by the immersion in SBF solution for 5 days.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.30-37
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• 2020

We propose a practical method for increasing formability of a sheet metal plate using laser heat treatment (LHT) and cladding process. In this work, two kinds of process such as laser-induced heat treatment and cladding were utilized to evaluate the effect on formability of SUS316 sheets with different thickness of 1 and 3 mm. By using a vertically line-patterned tensile specimen that was LHTed or cladded on its surface, the process parameters of each surface treating method were studied and optimized. Through the basic test, we knew that the laser power of 900 W and scanning speed of 500 mm/min was the best condition for increase of formability. As the treatment results, ultimate tensile strength and elongation were increased as approximately 2.1 and 7.0%, respectively. To verify the usefulness of this work in industrial cases, we conducted a bulging test using with and without LHTed SUS316 sheet metal blanks. The results show that the bulging height of LHTed sheet was increased by 73% compared to that of the original one.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.5
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• pp.232-238
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• 2020

Heating experiments using the 7075 aluminum alloy in the state of billet and extrudate have been performed to investigate the pertinent ranges of working temperatures and holding times for the application to the various automobile parts. The 7075 specimens from raw billet of 152 mm in diameter and 400 mm in length prior to extrusion were used for heating with a holding time of 10 minutes at temperatures between 380℃ and 550℃. Then, an extrusion process using the billet has been fulfilled at 380℃ with extrusion speed of 0.8 mm/min to get an plate-type extrudate of 75 mm in width and 4.2 mm in thickness. The samples from the extrudate were subjected to heating experiments at temperatures between 380℃ and 440℃ with holding times such as 10 min, 30 min, 60 min and 120 min at each heating temperature. The microstructures were investigated on the optical and EBSD micrographs. The hardness measurement and the tensile test have been performed to investigate the effect of the heat treatment on the mechanical property. The results showed for the 7075 extrusion process that the safe heating of billet can be performed below 450℃ and the extrusion can be done safely up to 400℃.