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슈퍼 오스테나이트계 스테인리스강 (UNS S31254)의 용접 및 용접 후 열처리 상태에서의 부식거동
조동민,박진성,정원기,홍승갑,김성진 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.6
The corrosion behaviors of a combined weld (plasma, gas tungsten arc) joint in a super austenitic stainless steel pipe were investigated using a range of experimental and analytical methods. To ensure superior corrosion resistance, a Ni-based super alloy (Inconel 625) was employed as the welding material only in the gas tungsten arc welding (GTAW). Nevertheless, pitting corrosion occurred preferentially around the sigma phase which had been precipitated in the interdendritic region of the GTAW. This indicated that the Inconel 625, which has a higher pitting resistance equivalent number (PREN), became even more susceptible to pitting corrosion than the base metal (BM). The higher Fe content in the Inconel 625 due to the dilution of Fe, supplied by the leading plasma arc welding, may increase the driving force for the precipitation of sigma phase. It was also revealed that the post weld heat treatment conducted at 1050~1150 oC effectively reduced the fraction of sigma phase precipitated in the weld. Even after such heat treatment, however, pitting corrosion occurred unexpectedly in the center region of the BM. This may be due to additional precipitation of the sigma phase in the BM, caused by inadequate control of the cooling rate during heat treatment at the industrial site.
공용중인 교량 바닥판 콘크리트 보수를 위한 개질유화아스팔트를 이용한 초속경 라텍스 개질콘크리트 교면포장 공법(BLMC-VE공법)
조동민,박태순,신현국 한국아스팔트학회 2023 한국아스팔트학회지 Vol.13 No.1
BLMC-VE (Very-Early Strength latex modified concrete using modified emulsified asphalt) enables early traffic opening in 4 hours after completion of concrete laying, and has excellent adhesion strength, chloride ion penetration resistance, freeze-thaw resistance, crack resistance, durability. Using its characteristics, it is used for overlaying bridge decks or concrete road pavement repair work. By completely removing the old bridge deck concrete and then paving the bridge surface, the load capacity is improved and the effect of structural repair and reinforcement is excellent. As a result of performance evaluation, BLMC-VE can prevent road icing at sub-zero temperatures and promote thawing at melting temperatures.
A516-65급 압력용기용 강재의 용접모사 열처리를 통한 용접열영향부의 수소확산 및 황화물응력균열 거동 연구
조동민,박진성,이진우,김성진 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.9
Hydrogen diffusion and sulfide stress cracking of simulated heat-affected zone (HAZ) of A516- 65 grade steel were examined using an electrochemical permeation technique, glycerin volumetric method, and constant loading method. HAZ samples were fabricated using a metal thermal cycle simulator with a welding heat input of 20, 35, and 50 kJ/cm. The fractions of bainite and martensite-austenite (M-A) constituent in coarse-grained HAZ (CGHAZ) and intercritical HAZ (ICHAZ) obtained by a simulated thermal cycle with a low heat input (20 kJ/cm) were higher than those with a higher heat input. These fractions contributed to the increase in the reversible hydrogen trap density (N[H]rev) and reversibly trapped hydrogen concentrations (Crev). Although CGHAZ had higher N[H]rev and Crev meaning that it is more likely to be vulnerable to brittle failure by hydrogen, actual fracture by sulfide stress cracking (SSC) occurred in ICHAZ composed of a mixture of soft ferrite/pearlite, and hard bainite and M-A. The hydrogen diffusion/ trapping parameters, which were obtained from the electrochemical permeation or glycerin method, cannot be directly indicative of the resistance to SSC of the steel in a H2S environment. The susceptibility to SSC was more influenced by the level of M-A-localization and localized corrosion attack, acting as a stress intensifier under a tensile load.
복부대동맥류의 혈관 내 치료 후 발생한 제2형 혈관누출의 자연경과
조동민,박근명,양신석,김나리,우신영,김영욱,박광보,박홍석,도영수,김동익 대한혈관외과학회 2011 Vascular Specialist International Vol.27 No.4
Purpose: Endovascular aneurysm repair (EVAR) for the treatment of abdominal aortic aneurysm (AAA)has shown excellent early outcomes. However, long-term durability continues to be questioned because of endoleaks. The optimal management of type II endoleaks remains controversial because little is known about their long-term natural history. The purpose of this study was to evaluate the natural history of type II endoleaks and to study factors associated with persistent type II endoleaks. Methods: On a retrospective basis, we analyzed 98 patients who underwent EVAR for incidence and outcome of type II endoleaks. Patients with type II endoleaks were evaluated using computed tomography angiography or Duplex scans at one, 6 and 12 months after their EVAR, and annually thereafter to evaluate both the persistence of the endoleak and the size of the aneurysm sac. Results: Type II endoleaks were detected during the follow-up periods in 38 patients (39.8%), who underwent EVAR (mean follow-up: 23.7 months). Spontaneous sealing of type II endoleaks by 6 months after EVAR occurred in 15 patients (39.4%), meaning that there were 23 patients (60.6%) whose leaks were ongoing for more than 6 months. Four patients were treated using embolization because of an enlarging aneurysm sac. Conclusion: Most type II endoleaks are transient and do not require intervention. However, particularly persistent endoleaks could lead to aneurysm enlargement and to delayed aortic rupture. We did not find a significant difference in any number of preoperative patient factors between patients with transient, persistent,or no type II endoleaks. Further studies based on independent data sets are needed to validate these results.
산성수용액 환경 내 슈퍼 오스테나이트계 스테인리스강 (UNS S31254)의 용접 및 용접 후 열처리 전 · 후 부식거동
조동민,박진성,홍승갑,김성진 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
국제해사기구 (International Maritime Organization, IMO)에서는 선박에서 배출되는 이산화탄소, 황산화물 및 질소산화물을 줄이기 위해 2020년 1월부터 배출 규제해역 외 모든 해역의 선박에서 배출되는 황 함유량을 감소시키는 등 규제를 대폭 강화하였다. 규제를 만족시키기 위해 최근에는 선박 내 스크러버를 설치하는 추세이다. 한편 스크러버에 적용된 강재는 황산화물이 다량 함유된 가스 정화 시 해수가 이용됨에 따라 부식 구동력이 높은 환경에 장기적으로 노출되어진다. 이에 따라 장기적 고내식 특성을 보증할 수 있는 소재가 요구되며, 경제성 측면에서 슈퍼 타입의 오스테나이트계 스테인리스 강재 (super austenitic stainless steel, SASS)의 적용가능성이 높게 평가되고 있다. 슈퍼 오스테나이트계 스테인리스 강재를 대상으로, 부품 및 설비 등의 형상 제작을 위해 용접이 수반되는데, 용접 시 모재와 용접부간 화학적 조성 및 입열량 등 용접조건에 따라 석출되는 이차상 입자들로 인해 소재의 기계적 특성 및 부식특성이 크게 달라질 수 있다. 이에 따라 기계적 특성 및 우수한 내식성 보증이 가능한 Ni기반의 Inconel 계 합금이 적용되나, 모재와 용접부 간 화학적 조성차이에 기인한 이차상 석출의 가능성이 존재할 수 있다. 따라서 이차상 입자의 형성 감소를 목적으로 용접 후 열처리 (post weld heat treatment, PWHT)가 수행되고 있다. 하지만 실제 산업 내에서 후 열처리 수행 시, 용접부 뿐 아니라 모재 영역 또한 열이력을 동일하게 받기 때문에 열처리-냉각 프로세스 과정에서 발생되는 미세조직적 변화와 이에 따른 부식거동 변화에 대해 보다 명확하게 이해할 필요가 있다. 따라서, 본 연구에서는 슈퍼 오스테나이트계 스테인리스 강재를 대상으로 플라즈마 아크용접과 가스 텅스텐 아크용접을 적용하여, 용접 후 열처리 전후에 따른 이차상 석출거동 차이 측면에서 공식개시에 대한 메커니즘적 원인을 규명하고, 고내식 특성을 보증하기 위한 용접 후 열처리 최적화 조건에 대한 바람직한 방향에 대해 제시하고자 한다.
고점도 아스팔트 바인더 종류에 따른 휨 특성 해석 수학적 모델링 개발연구
조동민,박태순,문기훈 한국아스팔트학회 2023 한국아스팔트학회지 Vol.13 No.1
Bending tests were performed under various temperature conditions for each type of high-viscosity asphalt binder. The displacement-time curve and the time-load curve recorded through the test process were derived and analyzed. Through this, even though the high-viscosity asphalt binder with the same PG grade, the bending stiffness and bending energy of each type do not satisfy the current standard. To develop a mathematical modeling that can quantitatively evaluate the low-temperature performance of high-viscosity asphalt binders, a time-load prediction formula in the form of an exponential-log function was developed and presented based on the results of the bending tests. The low-temperature performance of various high-viscosity asphalt binders was analyzed and evaluated in detail and quantitatively through parameter analysis of the presented mathematical model. As a result, it was derived that the low-temperature performance of the high-viscosity asphalt binder could be evaluated in more detail through the proposed mathematical model.