• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.557-564
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• 2009

Welding residual stress is occurred after welding process. Tensile residual stress is one factor of PWSCC. Repair welding usually happened during the manufacturing welding process. Repair welds cause strong tensile residual stress. In PWR, Repair weldments made by Alloy 82/182 is susceptible to PWSCC caused by tensile stress, material and environment. Therefore, mitigation of welding residual stress in weldments is important for reliable operating. PWOL is one of the methods for mitigation and verified for over twenty years. In this paper, residual stress distribution of repaired weldments and the effect of PWOL on mitigation is examined for surge nozzle.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.551-556
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• 2002

Solid particle erosion wear characteristics of high Cr white iron hardfacing were investigated using the erosion wear test method according with the ASTM G76-95. Wear experiments, where the blast angle, blast distance and blast pressure were selected as test variables, were planned and analyzed by response surface method (RSM to evaluate the wear loss statistically and quantitatively. The measured wear losses well coincided with the calculated ones by the experimental equation. The wear loss of high Cr cast iron hardfacing was increased with blasting pressure, but affected in a complicated way by the blasting angle and distance. Erosion wear of high Cr cast iron hardfacing could be well predicted by RSM analysis of wear variables.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.04a
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• pp.80-80
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• 2001

제지 공정의 효율적인 운영을 위한 수단으로 보류 및 탈수성의 분석은 매우 중요한 작 업 이 다. 보류 및 탈수 특성 을 평 가하기 위 하여 SR(Shopper-Riegler), CSF(Canadian S Standard Freeness tester) 그리고 원형 수초지기 등의 비난류 상태의 자연탈수 특성 평가 장치와 동적 조건의 감압식 탈수성 분석기 등이 사용되고 있다. 하지만 이것들은 제지 공정 에 보다 더 근접한 탈수 및 보류 특성을 평가하기에는 부족한 점이 있다. 특히 wet-end 첨 가제들의 효능을 보다 정확히 분석하는 것이 불가능하다. 이런 이유로 난류 발생과 감압 탈 수 둥을 유도한 탈수 특성 평가 장치 개발의 필요성이 커지고 있다. R RDA - HSF(Retention Drainage Analyzer- Handsheet Former)는 지료조성, 감압탈수 및 습지의 성형이 자동화되어 보류도와 탈수성, 종이지합 및 강도를 종합 평가 할 수 있는 새 로운 실험실용 초지기이다. 보다 현장에 가까운 초지 조건을 구현하기 위해서 지료의 농도 를 높이고 진공 탈수를 실시함에 따라 기존의 탈수성 분석기나 보류도 측정기의 단점을 보 완하게 되 었다. 본 연 구에 서 는 Canadian Standard Freeness test와 Dynamic Drainage Jar test 및 원 형 수초지기를 활용한 기존의 탈수성, 보류도 분석 결과와 RDA-HSF를 비교하여, 자연 탈수를 이용하는 기존의 탈수 및 보류 설비에 비해 현장 공정을 보다 현실적으로 재현할 수 있는 감압 탈수 초지 설비로서 RDA-HSF의 활용 가능성을 분석하였다. RDA-HSF를 활용한 실험실적 분석을 통해 현장의 상황올 유사하게 재현함에 따라 공정 운영 인자의 변화에 따른 제품의 품질 및 생산효율을 예측할 수 있게 된 바, 보다 효율적 인 공정 관리가 가능할 것으로 기대된다. 안료 입자의 경우 피인쇄체의 표면 공극을 채우고, 비히클의 경우 미세한 공극속으로 침투되어 경화됨으로써 피인쇄체가 지니고 있는 공극량을 감소시커 게 될 것이다. 그리고 피인쇄체의 각종 형태의 공극으로 침투된 잉크의 양에 반비례적으로 피인쇄체의 표변에 잉크가 잔류하게 될 것이다. 따라서 본 연구에서는 여러가지 안료를 사용하여 각각 다른 공극 특성을 지니는 도공지를 제조한 후 이들이 가지는 공극 특성과 잉크의 잔류 거동에 대해 고찰해 보고자 하였다.여 표면 유효층 일부만 오버레이시키며I 주조 및 단조가 불가능한 재료까지도 표면부에 오버레이 시킴으로 서 부품 및 설비의 제조에 있어 재료비의 절감과 제품의 수명이 획기적으로 개선될 수 있다. 그리고 최근에는 도금 빛 용사 둥과 같은 표면처리를 할 경우임의 소재 표면에 도금 및 용 사에 용이한 재료를 오버레이용접시킨 후 표면처리를 함으로써 보다 고품질의 표면층을 얻기위한 시도가 이루어지고 있다. 따라서 국내, 외의 오버레이 용접기술의 적용현황 및 대표적인 적용사례, 오버레이 용접기술 및 용접재료의 개발현황 둥을 중심으로 살펴봄으로서 아직 국내에서는 널리 알려지지 않은 본 기 술의 활용을 넓이고자 한다. within minimum time from beginning of the shutdown.및 12.36%, $101{\sim}200$일의 경우 12.78% 및 12.44%, 201일 이상의 경우 13.17% 및 11.30%로 201일 이상의 유기의 경우에만 대조구와 삭제 구간에 유의적인(p<0.05) 차이를 나타내었다.는 담수(淡水)에서 10%o의 해수(海水)로 이주된지 14일(日) 이후에 신장(腎臟)에서 수축된 것으로 나타났다. 30%o의 해수(海水)에 적응(適應)된 틸라피아의 평균 신사구체(腎絲球體)의 면적은 담수(淡水)에 적응된 개체의 면적보다 유의성있게 나타났다. 해수(海水)에 적응(適應

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.873-881
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• 2008

Weld overlay is one of the residual stress mitigation methods which arrest crack initiation and crack growth. Therefore weld overlay can be applied to the region where cracking is likely to be. An overlay weld used in this manner is termed a preemptive weld overlay(PWOL). In pressurized water reactor(PWR) dissimilar metal weld is susceptible region for primary water stress corrosion cracking(PWSCC). In order to examine the effect of PWOL on residual stress mitigation, PWOL was applied to a specific dissimilar metal weld of Kori nuclear power plant by finite element analysis method. As a result, strong compressive residual stress was made in PWSCC susceptible region and PWOL was proved effective preemptive repair method for weldment.

• Journal of Welding and Joining
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• v.2 no.1
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• pp.4-17
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• 1984

Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.176-176
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• 2000

Recently developed Austenite stainless steel,309L was to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also. the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied.1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained.2) The form of martensite at the transition region was occured by reversible transition region, leading to increasing Ms point.3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling.4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the grain boudary.(Received August 3, 1999)

• Journal of Welding and Joining
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• v.18 no.2
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• pp.49-56
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• 2000

Recently developed Austenite stainless steel, 309L was used to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also, the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied. 1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained. 2) The form of martensite at the transition region was occurred by reversible transformation during cooling since the interdiffusion of Cr and Ni from weld metal and Fe and C from base metals at the transition region, causes to lowering the concentration of Cr and Ni at the transition region, leading to increasing Ms point. 3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling. 4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the gain boundary.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.82-89
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• 2002

In order to clarify hot cracking phenomena occurred in Inconel 690 welds and it's prevention, in this study, the cracking behavior and the influence of welding variables on cracking in Inconel 690 overlay welds on Mn-Ni-Cr-Mo steel(SA 508 cl.3) for pressure vessel were investigated by using mock-up test. The main results are as follows: The cracks in Inconel 690 overlay welds were mainly generated near the start and the end part of welding beads adjacent to STS 309L welded outside of Inconel 690 welds. Most of the cracks showed typical solidification crack, and also it was assumed that there was possibility of liquation cracking in HAZ. The existence of Nb constituents or concentration of Nb was recognized on the fracture facets of the solidification cracks in the welds by SMAW. Therefore Nb was considered to be the main factor of the solidification cracking. As the weld heat input was more increased and the weld bead length was longer, the extent of cracking was more increased. Moreover the extent of cracking was considerably decreased by changing of welding sequence to the start and the end part of welds. Hot cracking in welds by GTAW was considerably decreased as compared with that of SMAW. And cracks were well generated in the Inconel 690 overlay welds adjacent to 575 309L welds. This means that the hot cracking susceptibility of Inconel 690 welds was largely varied by chemical components and/or compositions of filter metals, base metals and neighboring welds.

• Journal of The Korean Society of Grassland and Forage Science
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• v.18 no.3
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• pp.171-178
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• 1998

This experiment was conducted to study on forage utility of Diplachne fusca L. which live in reclaimed saline land of midwest region of Korea. The primary experiment was conducted to know on germination characteristics of Diplachne fusca L. according to storage condition after seed harvesting, light, temperature, flooding depth, salinity and soil covering. The results obtained are summarized as follows; 1. The germination percentage, average days to germination, germination rate and coefficient of germination were not different in existence of light, combination with existence of light and storage condition, but those were higher different in storage condition. 2. The germination characteristics were more higher on the condition of alternating temperature than constant temperature, and it was the highest on the condition of alternating temperature with $35/25^{\circ}C$ and constant temperature with $35^{\circ}C$. 3. There were apparently significant in germination percentage, average days to germination, germination rate and coefficient of germination according to flooding depth. The germination characteristics of D. fusca L. were the highest on the wndition of flooding depth with Ocm and did not germinate on the condition of flooding depth more than 3cm. 4. There were apparently significant in germination percentage, average days to germination, germination rate and coefficient of germination according to salinity. Germination characteristics were the highest on the condition of salinity with 0.2%. There was more than 30% of germination percentage on the condition of salinity with 1% SO Diplachne fuaca L. was suitable to cultivate in reclaimed saline land. 5. The germination percentage, average days to germination, germination rate and coefficient of germination were significantly difference between soil covering. So Germination characteristics were the highest on the condition of soil covering with 0.2cm. But they scarcely germinated on the condition of more than 1cm of the soil covering.