• Journal of the Korean Ceramic Society
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• v.43 no.1 s.284
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• pp.1-3
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• 2006

Well-shaped NaA zeolite cubic crystals of a large size of $5-7{\mu}m$ were synthesized by a hydrothermal method in a mother solution having a $3.55Na_2O:Al_2O_3:1.6SiO_2:593\~2000H_2O$ composition. Thermal treatment of NaA zeolite crystals resulted in the formation of a crystalline phase of $NaAlSiO_4-Camegeite$ between 800 and $900^{\circ}C$. Even at $1000^{\circ}C,\;NaAlSiO_4$ phase was found as a major product. Environmental Scanning Electron Microscopy (ESEM), High Resolution Transmission Electron Microscopy (HRTEM), X-Ray powder Diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, and DTA/TGA and BET analyses were used to characterize the initial materials and the obtained products after various heat treatments.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.730-735
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• 2000

The finite element analysis by the computer program SYSWELD in consideration of phase transformation was carried out to simulate the multi-pass welding process of SA106 Gr. C which is used for the main steam pipe in nuclear power plant. All the numerical results such as temperatures, the size of heat affected zone and the residual stresses were compared to the experimental results.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.2
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• pp.65-69
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• 2002

$Llo{\rightarrow}Ni_5Al_3$ reordering and related properties in Ni-Al alloys consisting of 64-65at%Ni are characterized by X-ray diffraction, shape memory effect and damping capacity. Formation of $Ni_5Al_3$ takes place by simple ordering of atoms with a continuous increase in c/a ratio. As a result, degradation of shape memory effect and damping capacity is observed after short time annealing at $200-300^{\circ}C$.

• Laser Solutions
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• v.3 no.3
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• pp.21-29
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• 2000

For the direct metal shape processing the powder feed device which is different from the widely used in rapid prototyping. is developed, The three dimensional object is shaped with the melting metal powder. The developed research has applied to rapid prototyping in ultraprecision for MEMS and medical science fields required of rapid manufacture of complex shape. The goal of this study make 3D model which has precision accuracy. Powder spreading apparatus has been more improved because that the control of powder spread is very important in layer manufacturing. It consists of the vibration motor, nozzle and tube which supplies various metal powder. This apparatus could control the spreading velocity that could control powder spreading thickness. Laser on/off switch was adapted because laser scanning velocity must be preserved constantly to prevent heat transformation of laser overheating. The error between sintered thickness md experimental one occurred by shrinkage in sintering melting process. The problem of heat transformation was solved by On/Off switching system.

• Corrosion Science and Technology
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• v.6 no.2
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• pp.56-61
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• 2007

Carbide dissolution during heating processes can change chemical composition of martensitic stainless steel in its austenitic phase. Although the austenitizing treatments were carried out at a homogeneous austenite region, the amount of carbon atom in the matrix differs. Increase in the amount of carbon contents in the matrix resulted in decreasing MS temperature, which consequently causes the volume fraction of the retained austenite to increase. This study reveals the effects of the austenitizing treatment on the properties of Fe - 0.3C - 14Cr - 3Mo martensitic stainless steel change with different austenitizing temperatures.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.824-828
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• 1990

Zirconia gel fibers were fabricated by sol-gel processing using zirconium alkoxides and 2, 4-pentanedione. Their phase transformation and microstructural evolution were studied after heat treatments up to 150$0^{\circ}C$. Tetragonal ZrO2 began to form at 50$0^{\circ}C$ and followed by monoclinic, tetragonal phase during subsequent heat treatments at 1000, 150$0^{\circ}C$ for 1hour respectively. During cooling from 150$0^{\circ}C$, cracks were created, propagated along grain boundaries due to the volume change from tetragonal to monoclinic transformation.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.14-21
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• 1999

The wave nature of heat conduction has been developed in situations involving extreme thermal gradients, very short times, or temperatures near absolute zero. Under the excitation of a periodic surface heating in a finite medium, the hyperbolic and parabolic heat conduction equations and the damped wave equations in heat flux are presented for comparative analysis by using the Green's function with the integral transform technique. The Kummer transformation is also utilized to accelerate the rate of convergence of these solutions. On the other hand, the temperature distributions are obtained through integration of the energy conservation law with respect to time. For hyperbolic heat conduction, the heat flux distribution does not exist throughout all the region in a finite medium within the range of very short times(${\xi}<{\eta}_l$). It is shown that due to the thermal relaxation time, the hyperbolic heat conduction equation has thermal wave characteristics as the damped wave equation has wave nature.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.192-199
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• 1998

This study was carried out to investigate the influence of variations in the temperature and time of isothermal heat treatment, applied stresses and prestrain on the isothermal transformation behavior of ${\gamma}$ and ${\sigma}$ phases and mechanical properties of 25Cr-7Ni-3Mo duplex stainless steel. The precipitation of ${\gamma}$ and ${\sigma}$ phases through isothermal heat treatment showed the type curves with a certain incubation period, the curve migrated to in a short period of time and the amount of precipitation increased with decreasing isothermal heat treatment temperature. Under the state of isothermal transformation, the precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by applied stress, with increasing applied stress, the curves migrated to in a short period of time and also observed that the application of stress has a greater influence on the amount of ${\sigma}$ precipitation than that of ${\gamma}$ precipitation. The precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by cold and warm rolling before isothermal heat treatment and precipitation of ${\gamma}$ and ${\sigma}$ phases has a greater influence on the warm rolling than cold rolling. The tensile strength and hardness increased with increasing cold and warm rooling reduction ratio.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.4
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• pp.247-255
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• 2005

Although heat treatment is a process of great technological importance in order to obtain desired mechanical properties such as hardness, the process was required a tedious and expensive experimentation to specify the process parameters. Consequently, the availability of reliable and efficient numerical simulation program would enable easy specification of process parameters to achieve desired microstructure and mechanical properties without defects like crack and distortion. In present work, the developed numerical simulation program could predict distributions of microstructure and thermal stress in steels under different cooling conditions. The computer program is based on the finite difference method for temperature analysis and microstructural changes and the finite element method for thermal stress analysis. Multi-phase decomposition model was used for description of diffusional austenite decompositions in low alloy steels during cooling after austenitization. The model predicts the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimates the amount of martensite also by using Koistinen and Marburger equation. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2000.11a
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• pp.47-47
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• 2000