• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.2
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• pp.148-156
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• 1994

Three composition in the system of $YO_{1.5}-BaO-CuO$ were grown using a cold crucible (skull) melting technique with a 50 kW R.F. induction generator operating at 4 MHz as the power source. The starting materials were prepared by conventional ceramic powder processing methods, loaded into the skull, and melted at about $1200^{\circ}C$. For this study, compositions near the $YBa_2Cu_3O_X$ region were selected. The growth rates used ranged from 4 cm/hr to 0.25 cm/hr. The relation between the microstructures and the starting composition of each ingot was determined using metallograph, X-ray diffraction, and energy dispersive X-ray analysis. Both $YBa_2Cu_3O_X$ and $Y_2BaCuO_5$ needle-shaped crystals, aligned with the growth direction, were formed in the $CuO-BaCuO_2$ eutectic matrix of the $YBa_2Cu_7O_x and YBa_5Cu_{11}O_x$ ingot.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.46-46
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• 2009

과거 고강도강 용접부에서 발생하는 저온균열은 주로 용접열영향부에서 발생하였는데, 이러한 문제점을 해결하기 위하여 강재 메이커들은 고강도강의 용접성을 향상시키고자 노력하였다. 이러한 노력의 결과로 TMCP, HSLA 강 등이 개발되었고 이들 강재는 예열온도를 저하시킬 수 있다는 장점 때문에 보편화되어 사용되었다. 이러한 강재는 모재 예열온도를 기준으로 적용하게 되면 용착금속에서 저온균열이 발생하는 경우가 있다. 따라서 이제는 용접재료의 용접성, 즉 용접재료의 저온균열 저항성을 평가 할 수 있는 기법이 요구된다. 본 연구의 목적은 용착금속의 저온균열 저항성을 평가하는 것인데, 저온균열 저항성은 용착금속의 미세조직에 따라 다르게 나타날 수 있다. 용착금속의 합금조성은 기본적으로 용착금속에 요구되는 최저 강도와 충격인성을 만족할 수 있도록 설계한다. 하지만 유사한 강도의 유사한 합금조성이더라도 일부 합금 성분에 의해 용착금속의 미세조직들은 상이하게 나타날 수 있는데, 미세조직 특성에 의하여 용착금속의 강도와 저온인성이 결정된다. 용착금속의 저온균열 저항성을 평가하기위하여 Gapped Bead-on-Groove(G-BOG) 시험에 사용된 모재는 50mm 두께의 mild steel을 사용하였으며, 모재의 희석을 방지하기위해 15mm 깊이로 V-groove 가공 후 buttering 용접 하였다. 용접된 시편은 다시 5mm 깊이로 V-groove로 2차 가공 후 Ar + 20% $Co_2$ gas를 사용하여 용접하였다. 용접재료는 ER-100S-G grade로 비슷한 합금조성을 갖는 2 종류를 사용하였다. A용접재료는 Ti 이 0.1% 함유 되었으며, B용접재료는 Ti 함유되지 않은 것을 사용하였다. 또한 예열 온도에 따라 저온균열 감수성을 평가하기위하여 모재의 예열온도를 각각 상온, $50^{\circ}C,\;75^{\circ}C,\;100^{\circ}C$로 하여 실험을 진행하였다. 용착금속의 미세조직을 확인해본 결과 Ti 함유된 A 용착금속 미세조직은 대부분 침상형페라이트로 나타났으며, Ti 함유되지 않은 B 용착금속 미세조직은 대부분 베이나이트로 나타났다. G-BOG 시험 결과 Ti 함유된 A 시편이 Ti 함유되지 않은 B 시편보다 저온균열 발생량이 적었다. 이는 용착금속의 미세조직분포 및 특성에 따라 저온균열감수성이 다르다는 것을 나타낸다.

• Journal of Welding and Joining
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• v.14 no.1
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• pp.68-74
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• 1996

The microstructure of HAZ and the mechanical properties in weldments such as hardness and toughness were studied for mild steel and AH36 grade TMCP steel, as increasing heat input with electrogas welding process. The results of this study can be summarized as follow: 1) In the HAZ of mild steel, the width of coarse grained zone was larger than that of the nomalized zone, however in the case of TMCP steel, the nomalized zone was wider than the coarse grained zone. 2) The grain size of HAZ become coarse with increasing heat input. And at the same heat input, the grain size of TMCP steel was more coarser than that of mild steel. 3) According to the change of heat input, the deviation of hardness values was not significant, and the maximum values of hardness was not in HAZ but in the weld metal. And the hardness values in root part was higher than in face part. 4) Even though the HAZ grain size of mild steel was larger than that of TMCP steel, the impact values for mild steel was higher than those for TMCP steel, and the impact values in face part was higher than those in root part.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.68-74
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• 2011

This papers investigated the mechanical characteristics and the weldability of identical as well as dissimilar welding by GTAW for STS 304 and STS 316L. It is applied to double wall gas pipe of duel fuel engine for LNG carrier. Consequently, the weldability of dissimilar and identical welded zone of STS 304 decreased compared to base metal significantly. The result of microstructure observation for welded zone, a degree of acicular ferrite in welding zone for STS 304 presented more than STS 316L. The hardness of welding zone for STS 304 presented higher value than that for STS 316L by this effect.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.46-56
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• 1996

HAZ impact toughness of Ti-oxide steel was investigated and compared to that of a conventional Ti-nitride steel. Toughness variations of each steel with weld peak temperatures and cooling rates were interpreted with microstructural transformation characteristics. In contrast to Ti-nitride steel showing continuous decrease in HAZ toughness with peak temperature, Ti-oxide steel showed increase in HAZ toughness above $1400^{\circ}C$ peak temperature. The HAZ microstructure of the Ti-oxide steel is characterized by the formation of intragranular ferrite plate, which was found to start from Ti-oxide particles dispersed in the matrix of the steel. Large austenite grain size above $1400^{\circ}C$ promoted intragranular ferrite plate formation in Ti-oxide steel while little intragranular ferrite plate was formed in Ti-nitride steel because of dissolution of Ti-nitrides. Ti-oxides in the Ti-oxide steel usually contain MnS and have crystal structures of TiO and/or $Ti_2O_3$.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.659-664
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• 1998

Densification behavior of $Si_3N_4$ ceramics by two step gas pressure sintering was compared with pres-sureless sintering one step gas pressure sintering or hot isostatic pressing. While it was difficult to get the highly interlocked ${\beta}-Si_3N_4$ microstructure during the pressureless sintering due to decomposition above $1800^{\circ}C$ gas pressure sintering could solve this problem by increasing the densification temperature 2MPa of nitrogen pressure was enough to inhibit the decomposition up to $1890^{\circ}C$ and especially two step gas pres-sure sintering applying comparatively low pressure(2MPa) until the closed pore stage and then high pres-sure(10MPa) after pore closure could increase the hardness and the toughness.

• Korean Journal Plant Pathology
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• v.12 no.1
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• pp.116-120
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• 1996

Water-soaked spots or lesions were observed on fruits or stems of melon plants at house-melon farms in Andong, Korea. The symptoms developed to soft rot of the fruits of wilting of the whole plants. The causal organism isolated from the water-soaked le-sions was identified as Erwinia carotovora subsp. carotovora based on the morphological and physiological characteristics. The causal bacterium was susceptible to not only two kinds of medical antibiotics but also two kinds of agrochemicals tested. Since the bacterial soft rot is a first described bacterial disease in melon in Korea, we propose to name the disease as "bacterial soft rot of melon".

• Journal of the Mineralogical Society of Korea
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• v.13 no.2
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• pp.96-114
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• 2000

춘천 연옥은 색깔에 따라 세가지 유형 (연녹색, 암녹색, 및 회색 연옥)으로 구분되고 이들은 각기 서로 다른 조직과 조성을 나타낸다. 연녹색 연옥이 이중에서 가장 일반적인 유형이다. 연옥은 주로 극미립의 연옥질 투각섬석으로 구성되고 여기에 미량의 휘석, Mg-녹니석 및 방해석이 불순물로서 수반된다. 연옥질 투각섬석 결정들은 그 폭이 5$\mu\textrm{m}$ 이하의 극미립질 침상 결정형을 이루며 서로 치밀하게 얽혀있는 연옥 특유의 조직을 나타낸다. 주사전자현미경 하에서 (110)의 벽개면의 발달이 현저하고, 주사탐침현미경 하에서는 벽개면을 가로지르는 방향으로 특징적인 조선이 나타나는 것이 특징이다. 연옥질 투각섬석은 투과전자현미경 하에서 흔히 단쇄형과 복쇄형이 결합한 3중쇄형 격자가 복쇄형의 투각섬석 구조 내에서 불규칙적으로 협재되는 혼성격자 구조가 발달하는 것이 특징이다. 드물지만 5중쇄형 격자와 4중쇄형 격자도 관찰되는데, 이 같은 불규칙한 격자 혼재상은 회색 연옥에서 보다 현저한 경향을 보인다. 이와 같은 혼성격자 구조형의 존재는 춘천 연옥이 열역학적으로 비평형 상태에서 형성되었음을 시사하는 것으로 여겨진다. 리트벨트법에 의한 구조검증을 통해서 구해진 연옥질 투각섬석들의 격자상수 값들은 X-선회절의 경우, a=9.837(1)~9.9804(4)$\AA$, b=18.046(2)~18.062(1)$\AA$. c=5.2765(7)~5.2803(3)$\AA$, $\beta$=104.717(9)~104.786(3)$^{\circ}$로 계산되었다. 이에 비해서 중성자 회절법에 의해서 측정되 격자 상수 값은 a=9.8841(6)~9.8933(7)$\AA$, b=18.1429(7)~18.161(2)$\AA$, c=5.3024(3)~5.3060(7)$\AA$, $\beta$=104.698(7)~104.771(4)$^{\circ}$로서 X-선회절에 의한 값들과 약간의 차이를 보인다. 연옥질 투각섬석은 Ca에 대한 Mg의 치환에 의해 M(4) 자라의 크기가 작아지면서 b축의 단위포도 함께 줄어드는 결정화학적 특징을 나타낸다. 이는 중성자 회절분석에 의해서 구해진 M(4)의 자리점유율과 M(4)-O의 원자간 거리에 의해서도 확인된다. 그러나 연옥질 투각섬석에 대한 리트벨트법에 구조검증 결과는 연옥의 유형별 미시적 광물상과 혼성격자 구조형의 특징에 별다른 연계성이 없는 것으로 나타났다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.33-37
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• 2008

The effects of Cu and Sb on the microstructure and mechanical properties of Sn-Sb-Cu-Ni-Cd whitemetal were investigated. Any compound phase was not observed in the whitemetal with 0.05 wt% Cu, while as the Cu content was increased, star- or needle-like $Cu_6Sn_5$ phases were found. The tensile strength gradually increased with Cu up to 5 % and then remained almost constant with Cu content above 5 %, while the hardness continuously increased with Cu content because of the increased hard $Cu_6Sn_5$ phases. As the Sb content increased, SbSn cuboids were present as well as $Cu_6Sn_5$. The tensile steength and hardness continuously increased and the elongation decreased with Sb content.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.1
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• pp.31-35
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• 2002

Abstract Spinel powder having a particle size of 0.9$\mu$m was calcined for 30 min at $1300^{\circ}C$, followed by ball milling for 4h, to obtain the spinel particle size of 3.29$\mu$m. The die-pressed spinel was presintered at $1100^{\circ}C$ for 2h and then lanthanum aluminosilicate glass was infiltrated at $1080^{\circ}C$ for 0~2 h to investigate the penetration kinetics in glass-spinel composite. The infiltration distance is parabolic in time due to capillarity. The strength and the fracture toughness of glassspinel composites were 317 MPa and 3.56 MPa $m^{1/2}$ respectively and dual microstructure of column (needle) and polygonal shapes as a result of recrystallization was observed due to the high calcination temperature.