• Journal of Welding and Joining
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• v.5 no.1
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• pp.16-22
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• 1987

오스테나이트계 스테인레스강 용접부의 .delta.-페라이트 생성인자에 관한 위의 실험결과로부터 아래의 결론을 얻을 수 있다. (1) 오스테나이트계 스테인레스강 용접부의 .delta.-페라이트는 에너지적으로 불안정한 상으로서, 오스테나이트로의 변태가 비가역적(irreversible)이다. (2) .delta.-페라이트의 생성 및 변태에는 합금원소의 확산이 반드시 수반되며, 최종 .delta.-페라 이트 함량은 정성적으로 다음과 같이 표시된다. 페라이트함량=primary페라이트-변태한 페라이트 (3) .delta.-페라이트 생성에 일차적으로 영향을 미치는 이자는 화학조성(Cr-당량/Ni-당량)이며, primary 변태양상 및 냉각속도에도 크게 의존한다. (4) 용착부 .delta-페라이트는 대개 Vermicular와 Lathy의 혼합조직으로 존재하며, 열영향을 받 을수록 에너지적으로 안정한 Globuar 형상으로 변해간다.

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.29-39
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• 2011

With regard to steel construction, many studies have been performed to examine the structural behavior of the bolted connections domestically and in other countries. Especially, a domestic study was conducted on the block shear fracture and shear lag effect on the single-bolted angle connection in carbon steel. In this study, specimens were prepared with the end distance parallel to the loading direction and bolt arrangement ($1{\times}1$, $1{\times}2$), as the main variables. Then the fracture mode and the curling effect on the bolted angle connection in austenitic stainless steel were investigated. Moreover, the fracture mode and ultimate strength were compared, and the strength reduction by curling was estimated.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.35-45
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• 1988

오-스테나이트계 스테인레스강에 대한 용접은 용접재료의 개발과 더불어 각종 산업계에 널리 이용되고 있으며 최근 Type 303 오-스테나이트계 스테인레스강 등은 free machining재로써 널리 응용되고 있다. 그러나 이 303계는 피삭성, 절삭성, 칩형성개선을 위한 특수원소(Se, S 등)의 첨가 때문에 용접성에 문제점을 제기하고 있다. 본 연구에서는 Type 303을 중심으로 AISI 304-316NG 및 347NG계의 오-스테나이트계 스테인레스강의 고온연성거동과 고온균열감수성(용접성)에 관한 연구에 대한 검토중 고온연성거동에 관하여 조사하였다. 고온연성평가는 Gleeble Simulator에 의하여 재료와 방향성에 따라 검토하였으며, 그 결과 모든 재료는 압연방향을 종방으로 시험하였을 때는 거의 유사한 고온연성을 나타내었으나 횡방향으로 시험하였을 때는 종방향에 비하여 연성저하를 나타내었다. 이와 같은 고온연성은 후속연구에서 검토될 고온균열 감수성과 밀접한 관련성에 의하여 용접성을 평가할 수 있다.

• Journal of Welding and Joining
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• v.5 no.3
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• pp.38-45
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• 1987

An investigation was conducted to find out the factors influencing on the impact toughness of austenitic-and duplex stainless steel weld metal. Various welding process with commerically available consumables was adopted to get weld doposited metal. The oxygen content of each weld metal was very sensitiive to welding process, involving flux composition, shielding gas and structural features. The results of this study show tat the content of oxygen as an oxide inclusion significantly affects impact toughness, and .delta.-ferrite distribution is also correlated with resultant toughness value.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.17-26
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• 2005

Dissimilar-metal welds(DHWs) are used widely in various industrial applications due to the pratical importance from the technical and economic aspect. However, DMWs have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMWs have used the various of heat source to decrease such as faults. In this paper, the weldability on dissimilar metal welds of Austenite stainless steel and Low carbon steel using a continuous wave Nd:YAG laser was experimentally investigated. Experiments were conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1560-1565
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• 2005

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.254-254
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• 2012

최근 친환경 에너지원 및 에너지 저감기술을 바탕으로 한 자동차 부품산업이 재편되고 있다. 그 중, 극한의 산화전해질 환경에서 견뎌야하는 연료전지 분리막 소재와, 자동차 연비향상을 위한 엔진소재 개발 경쟁이 가열되는 상황이다. 이러한 소재에는 공통적으로 고 내식성과 내 마모성의 특성이 요구되는데, 스테인레스강은 이러한 조건에 적합한 소재이다. 왜냐하면, 사용분위기에 의해 산화막이 두꺼워지고 이로 인해 저항이 증가하는 현상 때문에 연료전지 부품에 질화를 하여 이런한 현상이 일어나지 않으면서 내식성은 유지하기 때문이다. 하지만, 표면경도가 낮아 내 마모성 저하로 부품의 수명을 떨어뜨리는 단점이 있다. 따라서, 고 내식성 유지하되, 표면경도는 향상하는 기술이 필요한데, S-phase 과고용 질화기술은 이러한 문제를 해결할 것으로 보여진다. 하지만, 이러한 층의 형성에도 불구하고, 스테인레스강 자체 소재제작 과정에서의 품질문제 및 가공경화로 인한 문제와 더불어 질화처리 후 표면계질의 석출상이나 크랙형성으로 인해 내식성은 오히려 저감되는 문제를 지니고 있다. 이에 대한 대안으로, 표면 질화처리 후 침탄 공정을 추가 도입하였다. 따라서, 본 연구 에서는 기존 질화공정에서 내식성 저하원인에 대한 분석 및 고찰하고, 또한 새롭게 제안된 질화 침탄 기술을 통해 질소뿐만 아니라 탄소원자의 침입으로 내식성 저하를 방지하는 동시에 표면경도 향상하는 새로운 연구결과를 보여주고자 한다.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.56-60
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• 2011

A low temperature plasma carburizing process was performed to AISI 304L austenitic stainless steel to achieve the enhancement of surface hardness without a compromise in their corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface-hardened layer during low temperature plasma carburizng in order to obtain the optimum processing conditions. The expanded austenite (${\gamma}C$) was formed on all the treated surfaces. Precipitates of chromium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at $500^{\circ}C$. The hardened layer thickness of ${\gamma}C$ increased up to about $35\;{\mu}m$, with increasing treatment temperature. The surface hardness reached about 1000 $HK_{0.05}$, which is about 4 times higher than that of the untreated sample (250 $HK_{0.05}$). Minor loss in corrosion resistance was observed for the specimens treated at temperatures of $310^{\circ}C-450^{\circ}C$ compared with untreated austenitic stainless steel. Particularly, the precipitation of chromium carbides at $500^{\circ}C$ led to a significant decrease in the corrosion resistance.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.40-46
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• 1988

The effect of heat input on the content of residual .delta.-ferrite and the hot cracking susceptibility in the austenitic stainless steel overlaid on the carbon steel was studied in the range of heat input from 7.5 to 15.1 KJ/cm. Present study shows that residual .delta.-ferrite content in the overlay is mainly determined by the dilution of the base metal (carbon steel) which is in turn affected by heat input, i.e. the amount of dilution decreases as heat input increase. Accordingly, higher heat input results in a substantial increase in Cr equivalent but a little increase in Ni equivalent due to the less dilution of carbon from base metal. This fact can explain the result obtained in this study, i, e, the higher content of .delta.-ferrite in the weld deposit made with higher heat input. This in turn causes more resistant overlaying weld metal to hot cracking.