• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.173-176
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• 2009

A great emphasis has been placed on the design of heat treatment process to achieve desired microstructure and mechanical property of final product. In this study, finite element analysis was carried out to predict temperature, microstructure and hardness of eutectoid steel after water quenching. Convective heat transfer coefficients were determined by inverse analysis using surface temperatures measured with three different installation methods of thermocouples. Finally, the effect of convective heat transfer coefficients on the prediction of temperature history and hardness was analyzed by comparing experimental and simulation results.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.666-671
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• 2015

In this study, we investigated the effect of the residual carbides and tempered carbides precipitated by tempering treatment after quenching on the pitting corrosion of mod. 440A martensitic stainless steel. In quenched specimens and tempered specimens after quenching of mod. 440A martensitic stainless steel, the volume fraction of the residual carbides and total carbides decreased with the increase of the austenitizing temperature. Pitting resistance increased with the increase of austenitizing temperature. With the increase of the volume fraction of the residual and total carbides, the pitting resistance of mod. 440A martensitic stainless steel was decreased. The pitting resistance of mod. 0.5C-17Cr-0.5Ni 440A martensitic stainless steel had stronger affected by residual carbides than precipitated carbides produced by tempering.

• Nuclear Engineering and Technology
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• v.33 no.2
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• pp.166-174
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• 2001

An apparatus for detecting remote real-time uranium concentration using an optrode was developed. An optrode to detect uranium fluorescence as remote real-time control was designed. Fluorescence intensity at time 2ero was derived by the fluorescence signal processing and the algorithm to exclude the quenching effect of various quenchers and temperature fluctuations. This apparatus employing the above deriving method and the optrode has an error range within 6% in spite of serious fluorescence lifetime changes due to the quenching effect and temperature fluctuations. The detection limit is 0.06 ppm and the linearity is excellent between 0.06 ppm and 2 ppm on the aqueous uranium solution.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.201-204
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• 2000

Thermal shock resistance of 80Al2O3-20Al composite and monolithic alumina ceramics was compared. Fracture strength was measured by using a 4-pont bending test after quenching. Thermal stresses of the ceramics and ceramic-metal composites were calculated using a finite element analysis. The bending strength of the Al2O3 ceramics decreased catastropically after quenching from 20$0^{\circ}C$ to $0^{\circ}C$. The bending strength of the composite also decreased after quenching from 200~2$25^{\circ}C$, but the strength reduction was much smaller than for Al2O3. The maximum thermal stress occured in the monolithic alumina ceramics when exposed to a temperature difference of 20$0^{\circ}C$ was 0.758 GPa. The same amount of stress occured in the Al2O3-Al composite when the temperature difference of 205$^{\circ}C$ used.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.115-118
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• 1991

The temperature distribution on the superconducting thin-film is analyzed as moving constant field is applied above upper critical field. The distribution of magnetic field is derived in the normal spot. Governing equation is obtained with the help of the equation of conservation of energy. The temperature distribution and the heat dissipation are obtained through computer simulation by the method of numerical analysis. Maximum temperature is occured in the most right side inside normal spot. The temperature is increased abruptly inside the normal spot, and decreased more gradually outside normal spot in the direction of moving field as velocity is increased. Increasing the velocity rather than increasing magnitude of the normal spot and the applied field makes maximum temperature larger. Heat dissipation is affected by the velocity rather than the magnitude of normal spot and the applied field.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.828-830
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• 1988

This paper considered temperature-sensitive characteristics on the basis of curie tempeature and quenching method in the process of manufacturing Mn-Cu-Zn Fersite. The results are as follow. Curie tempeature drops according as the content of CuO and ZnO increases. It also decreases according as sintering temperature increases when the content of ZnO in fixed. Curie temperature drops more in quenching than in slow cooling and activation energy diminishes were too. On the basis of curie tempeature, activation energy is greater in paramagnetic region than in ferrimagnetic region. As its voltage-crrent characteristics is similar to that semiconductors, the temperature-sensitive ferrite is expeated to be appied in the area of power electronics.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.3
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• pp.206-214
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• 1999

The effect of cooling rate on carbide precipitation during quenching of austenitic manganese steel was investigated by optical microscopy, image analyzer and numerical analysis. A computer program based on the finite difference method for analyzing heat treatment processes was developed in order to evaluate cooling rates and the possibility of carbide precipitation during quenching. The area ratio of carbide precipitated in the austenite matrix was measured by the image analyzer, and used to determine the critical point of carbide precipitation. Temperature-dependent critical cooling rates at the critical points were calculated using the present simulation program, The calculated results showed a good agreement with the experimental ones.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.1
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• pp.7-13
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• 2013

Vacuum heat treatment(indirect heating method) has long exposure time at high temperature and low quenching rate. Contrarily salt bath heat treatment (direct heating method) has short exposure time at high temperature and fast cooling rate. With these different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study, Salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heat process and secondary hardening with high temperature tempering process. Consequently, It indicates that salt bath heat treatment is better way than vacuum heat treatment for product to have high mechanical properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.439-442
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• 2001

Chalcogenide glassy semiconductors(CGS) can be obtained by the melt quenching technique. We have investigated the thin film heterostructures : metal-chalcogenide glassy semiconductors, where metal is copper, and chalcogenide glassy semiconductors are glasses of the system As-Se. CU/CGS film heterostructure were produced in the vacuum evaporator by the method of vacuum thermal evaporation. Doped films are very sensitive to external actions, and this property allows developing supersensitive precision sensors of temperature, humidity, illumination, and etc. based on them. Cu/CGS film has shown that resistance strongly depend on the temperature. The ratio of resistance vs. temperature has shown over a 2 k$\Omega$/degree. The slop of temperature and resistance shows linear.

• Journal of Photoscience
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• v.3 no.1
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• pp.9-14
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• 1996

For three cultivars of chilling-sensitive cucumber plants, chilling sensitivity was evaluated in terms of photosynthetic activity using Chl fluorescence techniques. Low-temperature treatment caused a decrease in photosynthetic activities of cucumber leaves, measured as CO$_2$ exchange, as well as the decrease in the stomatal conductance. FR of the three cultivars decreased after chilling for 24 h in light and the extent of decline of F$_R$ was the greatest in 'Chosaeng' cultivar. When these plants were recovered from light-chilling, 'Chosaeng' and 'Samchuk' cultivars did not fully restore the original value of F$_R$ after 24 h of recovery, in contrast to 'Ilmi' cultivar which showed a rather efficient recovery. The results of FR study showed that 'Chosaeng' was most susceptible, whereas Ilmi was most resistant, to chilling among the three cultivars of cucumber plants. When quenching coefficients for chlorophyll fluorescence was analyzed after chilling the cucumber plants for 24 h in light, 'Chosaeng' elicited more rapid declines in the coefficients for photochemical quenching (qQ), non-photochemical quenching (qNP) and energy-dependent quenching (qE) than 'Ilmi' and 'Samchuk'. The implications of these observations are discussed in relation to the growth habits of the respective cultivars in the field. The results showed that measurement of chlorophyll fluorescence was an effective means of screening chilling tolerance of cucumber plants. Furthermore, the study on the chlorophyll fluorescence induction and fluorescence quenching charactersitics showed that low temperature could accelerate inhibition of photosynthesis in chilling-sensitive plants, by limiting Calvin cycle activity and disrupting, in part, the energy dissipation mechanims of the photosystem II.