• 한국압력기기공학회 논문집
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• 제20권1호
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• pp.25-31
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• 2024

The core shroud of rector vessel internals (RVI) of OPR1000 and ARP1400 is made of Type 304 stainless steel (SS) by bending and welding process that may induce high deformation and residual stress in manufacturing. This work aims to evaluate the susceptibility of stress corrosion crack (SCC) initiation of bent parts of RVI in high temperature primary water environment. For SCC initiation test, tensile specimens were fabricated from the 90 degree bent plate of Type 304 SS (DT specimen), that is an archived part of a Korean APR1400. After the SCC initiation test, the specimen surface was thoroughly examined by optical and scanning electron microscopy, and compared to the specimen fabricated from the as-received plate of Type 304 SS (AR specimen). The surface observation revealed that SCC initiated on the AR specimen surface in typical intergranular (IG) mode, while SCC on the DT specimen occurred in transgrannular mode as well as IG mode. It was also found that the size and number of SCC on the DT specimen were larger than that on the AR specimen. This was attributable to a strain-hardening during the bending process. To compare the susceptibility of SCC initiation, total crack density (TCD) was calculated from the total crack length divided by the measured area of AR and DT specimens. TCD of DT specimen was 4.6 times higher than AR specimen in average, indicating that higher possibility of degradation of bent parts of RVI for a long-term operation.

• 한국안전학회지
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• 제9권1호
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• pp.9-18
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• 1994

In this study, we conducted experimental tests to evaluate fracture behaviors of fresh-butt welded metal by Acoustic Emission technique. We selected similar welding and dissimilar welding process, the one welded for SM45C, SS41 and SUS304 of each material, the other for SM45C and SS41, SM45C and SUS304 and SS41 and SUS304. The fracturing processes of weld metal were estimatied through the fracture toughness test with compact tension specimens and fractography analysis. In ASTM test method E-399, type I curves for materials of this study were obtained by load-cod diagram of fracture toughness test. and 5% offset load( $P_{5}$) was estimated as the estimated crack initial load( $P_{Q}$), The estimated crack initial load( $P_{Q}$) of similar welding materials generally lower than base matal, and then SM45C appeared greatly in decreasing rate of PB, SS41 and SUS304 appeared in order. $P_{Q}$ of dissimilar welding materials were lower than the similar welding materials. $P_{Q}$ of welding of SM45C and SS41 appeared in small, SUS304 and SS41 appeared greatly in dissimilar welding materials. In fracture toughness test, AE counts increased before the inflection point of the slope, decreased after that. It was found that increasing of AE counts were due to the microcrack formation at the crack tip near the $P_{5}$ point through AE data. For welding materials in this study, both low and high AE amplitude appeared simulataneously. It was confirmed that the low AE amplotude was due to formation of micro void, micro crack or micro dimple, the high AE amplitude was caused by microvoid coalescence and quasi-cleavage fracture through analyses of fractograpy.apy.apy.apy.

• 한국표면공학회지
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• 제34권5호
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• pp.465-474
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• 2001

Type 304SS coatings were performed at 200$\square$ onto AISI 1045 carbon steel substrate using unbalanced magnetron sputtering (UBMS) with an austenitic AISI 304 stainless steel (SS) target of 100mm diameter. The total deposition pressure in the active Ar gas was 2$\times$10$^{-3}$ Torr. Coatings were done at various target power densities and bias voltages. Chemical compositions of metallic elements of the coatings were measured by energy dispersive X-rays spectroscopy (EDS). The structure and the morphology of Type 304SS coatings were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Corrosion properties of the coated specimens were examined using electrochemical polarization measurements and electrochemical impedance spectroscopy in a deaerated 3.5% NaCl solution. The porosity rate was obtained from a comparison of the dc polarization resistance of the uncoated and coated substrates. Scratch adhesion testing was used to compare the critical loads for different coatings. XRD results showed that the sputtered films exhibit a ferritic b.c.c. $\alpha$-phase. Potentiodynamic polarization curves indicated that all samples had much higher corrosion potential and better corrosion resistance than the bare steel substrate. The corrosion performance increased with increasing power density and the adhesion was enhanced at the bias voltage of -50V. An improvement in the corrosion resistance can be obtained with a better coating adhesion. Finally, an optimized deposition condition for corrosion protection was found as $40W/cm^2$ and -50V.

• 한국재난정보학회 논문집
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• 제20권2호
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• pp.411-418
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• 2024

연구목적: 본 연구에서는고인장 합금재를 활용하여 기존 철근콘크리트 기둥의 내진성능 향상이 가능한 새로운 형식의 볼트 체결식 내진보강재를 개발하고자 한다. 연구방법: 고인장 합금재인 SUS304 및 일반 구조용 강재인 SS275를 이용하여 T형 단면 강판을 제작하고 이를 SCM435의 고장력 볼트로 체결한 내진보강재 실험체를 제작하여 휨 실험을 통해 재료적 특성이 내진 보강성능에 미치는 영향에 대해 비교 분석한다. 연구결과: SUS304를 사용한 실험체가 7% 높은 최대 강도와 22% 높은 항복 강도를 보이며, 360MPa 더 높은 압축응력을 나타낸다. 또한 중립축의 변화도 더 미소하여 더 우수한 내력을 가진 것으로 판단된다. 결론: 동일한 단면에서 SUS304를 사용한 내진보강재가 휨 강도, 항복강도, 인장강도, 중립축 변화, 연성능력 측면에서 더 우수한 것으로 판단되며 추후 연구에서 철근콘크리트 기둥 실물 실험체에 적용함으로써 기둥-보강재간 일체 거동에 대한 실험이 필요하다고 사료된다.

• 방사성폐기물학회지
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• 제9권2호
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• pp.93-98
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• 2011

염분분위기에서의 부식은 사용후핵연료의 중간저장 기간동안 304 스테인레스 강재 건식저장용기의 주 열화기구들 중 하나다. 본 연구에서는 감소정도가 서로 다른 냉연 304 스테인레스 강 시편들에 0.5wt.%의 염화나트륨 연무를 분사시키면서 느린 변형속도시험(SSRT)과 중성염 분사시험(NSS)을 $85^{\circ}C$와 $200^{\circ}C$ 에서 수행하였다. $85^{\circ}C$에서 2000 시간 동안 시험한 NSS시편의 무게 변화는 $200^{\circ}C$에서 시험한 시편의 무게 변화와 크게 달랐다. NSS 시편의 $85^{\circ}C$에서 무게 감량은 미미하였지만, 냉연 감소율이 증가함에 따라서 무게 변화는 점진적으로 감소하였다. $85^{\circ}C$와 $200^{\circ}C$에서 그리고 염분분사 환경에서 가볍게 냉연 가공된 시편의 SSRT 시험으로부터 얻은 항복강도와 극한 인장응력의 값은 공기 중의 값보다 약간 낮았다. 그러나 염분 분위기에서 부식으로 인한 20% 감소 냉연시편의 강도는 더 이상 변화하지 않았다. 예비결과는 냉연 304 스테인레스 강의 질과 성능이 건식저장용기의 제작을 위한 조건에 맞는다는 것을 증명하였다. 그러나 냉연 스테인레스 강의 장기적인 성능을 더 잘 이해하기 위해서는 염분분위기에서 이 재질의 부식거동에 관한 더 많은 연구가 필요하다.

• 방사성폐기물학회지
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• 제12권3호
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• pp.199-209
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• 2014

가압경수로의 일차계통 제염을 위해 개발된 HYBRID 제염제의 재료부식 특성을 틈부식 시험방법을 사용하여 수행하였다. 기존 제염제의 부식특성과 비교하기 위하여 상용 제염제인 OA, CITROX 제염제의 부식특성도 함께 평가하였다. 시험재료는 가압경수로의 일차계통의 주 재료인 Alloy 600과 304 SS을 대상으로 시험하였다. 틈부식 시험은 가혹조건의 부식시험으로써 내식성이 강한 원전 구조재료의 건전성을 짧은 시간에 잘 확인할 수 있었다. 시험결과 OA와 CITROX 제염제에서는 crevice 시편 표면에 pitting과 IGA가 나타났으나 HYBRID 제염제에서는 국부부식이 전혀 발생되지 않았다. 무게감소 측정결과 HYBRID 제염조건에서는 $1.3{\times}10^{-3}{\mu}m/h$ 이하의 매우 낮은 부식속도를 나타내었다. 반면에, OA 제염제의 경우 Alloy 600은 $4.0{\times}10^{-2}{\mu}m/h$ 로 비교적 균일한 부식율을 나타내었으나, 304 SS의 경우 pH = 2.0 이하에서 급격한 가속부식을 나타내었다. HYBRID 제염제의 경우 일반부식에서뿐만 아니라 crevice 부식조건에서도 거의 부식이 일어나지 않아 PWR 계통제염 시 산화막 용해 후 제염제가 계통재료에 노출되어도 재료의 건전성이 입증되었다.

• Corrosion Science and Technology
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• 제9권6호
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• pp.331-337
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• 2010

This study compared the macro and micro electrochemical characteristics at the local area of welding metal on dissimilar welding parts for type 304 stainless steel (SS) and type 316L SS. The materials are used for double wall gas pipe of duel fuel engine for a ship. The various potentiodynamic experiments were performed several times in 10% ${H_2C_2O_2}{\cdot}{H_2O}$ solution using macro and micro methods, respectively. The micro electrochemical experiments conducted to resolve at local area on cross-section of dissimilar welding materials by micro-droplet cell device. The micro-droplet cell techniques can be used almost electrochemical experiments to resolve corrosion characteristics of the limited electrode area of the metallic surface between wetted spot of working electrode and tip of sharpened capillary tube. The results of macro electrochemical experiments show that resistance of active dissolution reaction at welding zone was high due to low current density by formation of passivation protection film at passive region. According to the micro electrochemical experiment, the corrosion current density of welding zone and bond zone were relatively high.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.260-265
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• 2002

Microbiologically influenced Corrosion (MIC) is one of the most deleterious effects of metal microbe interactions. When a fresh metal surface comes in contact with a non-sterile fluid, biofilm formation is ensued. This might result in the initiation of corrosion. The sites and materials where MIC is implicated are versatile. Industries such as shipping, power generation, chemical etc are reported to be affected. The rapid and unexpected failure of AISI type 304 stainless steel was investigated in the laboratory by simulation studies for a period of 4 months. Slime and water samples from the failure site were screened for corrosion causing bacteria. Both aerobic and anaerobic nora were enumerated and identified using PCR techniques. Pseudomonas sp. and Bacillus sp. were the most common aerobic bacteria isolated from the water and slime samples, whilst sulfate reducing bacteria (SRB) were the major anaerobic bacteria. The aerobic bacteria were used for the corrosion experiments in the laboratory. Coupon exposure studies were conducted using a very dilute (0.1%V/V) nutrient broth medium. The coupons after retrieval were observed under a Scanning Electron Microscope (SEM) for the presence of MIC pits. Compared to sterile controls, metal coupons exposed to Pseudomonas sp and Bacillus sp. showed the initiation of severe pitting corrosion. However, amongst these two strains, Psudomonas sp. caused pits in a very short span of 14 days. Towards the end of the experiment, severe pitting was observed in both the cases. The detailed observation of pits showed they vary both in number and shapes. Whilst the coupons exposed to Bacillus sp. showed widely spread scales like pits, those exposed to Pseudomonas sp. showed smaller and circular pits, which had grown in number and size by the end of the experiment. From these results it is inferred that the rapid and unexpected failure of 304 SS might be due to MIC. Pseudonwnas sp. could be considered as the major responsible bacteria that could initiate pits in the metallic structures. As the appearance of pits was different in both the tested strains, it was thought that the mechanisms of pit formation are different. Experiments on these lines are being continued.

• Design & Manufacturing
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• 제7권1호
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• pp.28-33
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• 2013

During the cold forming, due to high working pressure acting on the die surface, failure mechanics must be considered before die design. One of the main reasons of die failure in industrial application of metal forming technologies is wear. The mechanisms of wear are consisted of adhesion, abrasion, erosion and so on. Die wear affects the tolerances of formed parts, metal flow, and costs of process. The only way to control these failures is to develop a prediction method on die wear suitable in the design state in order to optimize the process. The wear system is used to analyse 'operating variables' and 'system structure'. In this study, with AISI D2, AISI 1020, AISI 304SS materials, a series of the wear experiments of pin-on-disk type to obtain the wear coefficients from Archard's wear model and the upsetting processes are carried out to observe the wear phenomenon during the cold forming process. The analysis of upsetting processes are performed by the rigid-plastic finite element method. The result of the analysis is used to investigate the die wear the processes, and the analysis simulated die wear profiles are compared with the experimental measured die wear profiles.

• 농약과학회지
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• 제20권4호
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• pp.300-304
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• 2016

이 연구의 목적은 살포기의 종류에 따른 피레스로이드 농약의 노출량을 평가하고자 하였다. 피레스로이드계 농약의 노출을 평가하기 위하여 사과 농작업자의 소변중 피레스로이드계 농약의 대사물질을 평가하였다. 결과에서는 살포량이 SS기 살포 그룹이 동력분무기 그룹보다 높았다. 하지만, 살포량과 살포면적을 통제하기 위하여 다변량 분석법으로 분석한 결과 SS기 살포자와 동력분무기 살포자의 노출량은 차이가 없었다. 농약노출에 대한 정확한 모델을 만들기 위해서는 농약 노출에 관련된 인자들이 통제되어야하고 추가적인 연구가 필요하다고 할 수 있다.