• International Journal of Korean Welding Society
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• 제2권1호
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• pp.11-14
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• 2002

A metallurgical model for bainite transformation kinetics in the coarse-grained heat affected zone(CGHAZ) on the basis of an Avrami-type equation was studied. Isothermal transformation tests were carried out to obtain the empirical equations for incubation time and Avrami kinetic constants for C-Mn-Mo-Ni steel. The effect of prior austenite grain size(PAGS) on the reaction rate of bainite was also investigated. Compared with experimental transformation behavior of bainite, the predicted behavior was in good agreement. It was also found that a smaller grain size retard the bainite reaction rate, contrary to the classical grain size effect and this is considered to be caused by constraint of grain size to bainite growth.

• 한국결정성장학회지
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• 제11권3호
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• pp.127-131
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• 2001

산화물계의 액상소결시 액상량을 변수로 하여 입자형성이 입자성장 거동에 미치는 영향을 고찰하였다. 산화물계 모델로 구형입자의 경우는 MgO$CaMgSiO_{4}$계를 선택하였으며, 각진입자의 경우는 $Al_{2}O_{3}$/ $CaAl_{2}Si_{2}O_{8}$계를 선택하였다. 구형입자인 MgO의 경우 액상량 증가에 따라 입자크기가 감소하였으나,각진입자인 $Al_{2}O_{3}$ 입자의 경우는 계면지배과정에 의해 성장하는 반면, 거친 고상/액상계면을 지닐 것으로 예상되는 구형 MgO입자의 경우는 확산지배과정에 의해 성장하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.205-210
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• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Average crystal grain sizes of the material are $200{\mu}m$ and $1000{\mu}m$. For this material, ${\Delta}K_{th}$ is about $8MPa{\sqrt{m}}$ which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low ${\Delta}K$ regsion. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. The relationship between da/dN and the ${\Delta}K_{eq}$ was represented by narrow band regardless of the stress ratio.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1998년도 특별강연 및 춘계학술발표 개요집
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• pp.144-146
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• 1998

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.209.2-209
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• 2003

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2304-2311
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• 2021

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.

• 한국분말재료학회지
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• 제15권3호
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• pp.214-220
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• 2008

In this study, consolidation behavior and hardness of commercially available molybdenum powder were investigated. In order to analyze compaction response of the powders, the elastoplastic constitutive equation based on the yield function by Shima and Oyane was applied to predict the compact density under uniaxial pressure from 100MPa to 700MPa. The compacts were sintered at $1400-1600^{\circ}C$ for 20-60 min. The sintered density and grain size of molybdenum were increased with increasing the compacting pressure and processing temperature and time. The constitutive equation, proposed by Kwon and Kim, was applied to simulate the creep densification rate and grain growth of molybdenum powder compacts. The calculated results were compared with experimental data for the powders. The effects of the porosity and grain size on the hardness of the specimens were explained based on the modified plasticity theory of porous material and Hall-Petch type equation.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.126-127
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• 2006

In this study, nano grain W is fabricated by Severe Plastic Deformation-Powder Metallurgy (SPD-PM) process. W powder and W-Re powder mixtures are processed by SPD-PM process, a Mechanical Milling (MM) process. As results, a nano grain structure, whose grain size is approximately 20nm, is obtained in W powder after MM for 360ks. A nano grain W compact, whose grain size 630nm, has excellent deformability above 1273K. A nano grain W-10Re compact is composed of equiaxed grain, a grain growth is restrained and has low dislocation density after the large deformation; therefore it is considered that W-Re compact shows superplasticity.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.216-216
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• 2009

$(Ni_{1-x-y}Zn_xCu_y)Fe_2O_4(x=0.45,\;0{\leq}y{\leq}0.3)$ was synthesized by conventional ceramic processing, and the sintering behavior and the magnetic properties of which were studied as functions of CuO content and sintering temperature. Both the densification and the grain growth rates were significantly enhanced with the increase of CuO content, while abnormal grain growth occurred when the samples of $y{\geq}0.2$ were sintered above $950^{\circ}C$. Saturation magnetization and coercive field were mainly influenced by the densification and grain growth of the specimens, respectively.

• 연구논문집
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• 통권23호
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• pp.15-27
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• 1993

The single crystal specimens were solidified by modified Bridgeman method. The surface recrystallized single crystal specimens were prepared by shot peening followed by heat treatment. The surface recrystallization begins at the dendrite cores on the surface. The recrystallized grains grew into the inner side of the specimen. The growth of recrystallized grains was inhibited by the pores and eutectic phases. The primary $\gamma'$ phases were dissolved at the recrystallized grain boundaries during the grain growth. The grain growth of recrystallized grains was similar to the cellular type transformation. No orientation relationships were found bewteen the recrystallized grains and the parent phase.