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Ni가 첨가된 고망간 용접봉의 입열량에 따른 인장 특성과 미세조직의 영향
한일욱(Il-Wook Han),윤중길(Jung-Gil Yun),이봉근(Bong-Geun Lee),강정윤(Chung-Yun Kang) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.1
The cryogenic high manganese steel is designed for tanks that transport liquefied natural gas, which has increased in demand globally. For this purpose, high manganese steel weld wire with ni added for Flux Cored Wire welding was welded under various heat input conditions. Then, a tensile test was measured to evaluate the mechanical properties. As a result, the heat input condition satisfying the required yield strength was 1.5 kJ. The reason for this phenomenon is that a small amount of Cu contained in the base metal and the welding rod is generated in grain boundaries of Cu₂O during solidification, causing liquefaction cracking.
고(<24%)Mn 플럭스코어드와이어를 사용한 다층 용접 시 초층 응고조직의 결정면방위에 따른 미세조직과 경도
한일욱(Il-Wook Han),엄정복(Jung-Bok Eom),윤중길(Joong-Gil Yun),이봉근(Bong-Geun Lee),강정윤(Chung-Yun Kang) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
In this study, Microstructure and hardness of 1st layer with crystallographic orientation were investigated about solidification structure in multipass weld using high Mn-Ni flux cored wire. Microstructure of solidification consisted of austenite matrix and a little ε-phase in grain boundaries. Orientation of grains was usually (001), (101), (111). According to crystallographic orientation, morphology of primary dendrite was different. The depletion of Fe and the segregation of Mn, C, Ni, Si, Cu, Cr, O were found along the grain boundaries. The area of segregation was wide with an order of (001), (101), (111) grains. And hardness of grains with crystallographic orientation increased with an order of (001), (101), (111) grains because of the segregation along dendrite boundary.
FCAW에 의한 590MPa급 고장력압력용기강의 초층편면용접부에서 발생하는 고온균열
김우열,한일욱,유덕상,방한서,안용식,박화순 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.5
It is well known that solidification cracking often occurs in welds of root pass for one-side welding under the conditions of high welding currents and speeds. In this study, the solidification in 590MPa class steel for pressure vessels SPPV490 was investigated by using flux-cored arc welding(FCAW) with 4 types of welding wires and welding conditions of 200∼280A and 2.8∼ 4.2mm/sec. In order to compared the result of cracking in SPPV490, 0.2%C steel for welded structure of SWS400 and 0.45%C steel for machine structural SM45C were also used as base metals. As the results, all the cracks formed in some welding conditions were observed near the center of weld bead. The solidification cracks were generally initiated near the upper surface of bead and propagated toward the inner part. The solidification cracking generally increased with welding current and welding speed in the same base metal and welding material. In cracking susceptibility, SPPV490 showed higher cracking susceptibility than SWS400 in all welding conditions and welding materials. It was considered that cracking susceptibility could not be evaluated with the hardness of weld metals. The cracking ratio increased with decreasing of a/b(a and b; the width of the upper surface and the back surface of the bead) as shape factor of bead. The cracking tendency with shape factor of bead was extended under the condition of higher welding currents.
Comparison of the Effects of Fluorides in Rutile-Type Flux Cored Wire
방국수,정홍철,한일욱 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.3
Various fluorides, CaF2, Na3AlF6, K2SiF6, MnF3, and MgF2, were added to rutile-type flux cored wires at concentrations of 1.8-2.3% and their effects on hydrogen reduction in weld metals were studied. All the fluorides reduced the hydrogen content but there were differences in the levels of reduction among the wires;CaF2 showed the greatest reduction and MnF3 showed the least. The hydrogen content in the weld metals was not influenced by the fluorine formed in the arc but by the slag basicity due to the small amount of fluorides added. The weld metal with higher slag basicities had a lower hydrogen content. The effects of fluorides on the arc stability, weld metal hardness, and microstructure were also examined. Because of the higher ionization potential of Mn, the wire containing MnF3 had the most unstable arc during welding. The wire containing MnF3 also produced a lower weld metal hardness than the other wires owing to its lower weld metal hardenability due to the greater oxidation loss of the C, Si, and Mn elements during welding.
임웅택,성대희,김진경,한일욱,박정웅,안규백 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
최근 선박의 대형화가 지속적으로 진행됨에 따라 해상에서도 환경오염에 대한 관심이 높아지고 있다. 또한, 지구온난화로 온실가스 배출에 대한 환경규제도 강화하는 움직임이 있으며 국내를 포함한 미국, EU등 선진국들은 배출가스 통제구역을 관리하고 있다. 선박의 경우도 LNG, 수소, 암모니아 등 친환경 에너지로 추진하는 선박에 관한 연구가 진행되고 있으며, 그 중 LNG는 현재 사용 가능한 친환경 연료로 부각되었으며, 많은 선박이 LNG 추진선으로 발주되고 있다. LNG 추진선은 LNG 저장탱크를 사용하는데 이중 B-type과 C-type 탱크가 일반적으로 많이 사용되고 있다. 현재 사용되고 있는 IGF코드에 등재된 극저온용 강재는 Al-alloy, 오스테나이트계 STS강, 9%Ni강 이 있다. 종래의 극저온용 강재는 용접성과 경제성에 문제들이 있어서 최근에 Mn의 함량을 고Mn강이 개발되어서 극저온용 강재로서 사용 가능성에 대한 연구가 진행되고 있다. 극저온용 강재로서 LNG 연료탱크는 제작되어도 각종 파이프와 연결이 되어야 하고 대부분의 파이프는 STS 강재로 되어 있어서 이재용접이 필수적으로 발생하게 된다. 본 연구에서는 현재 사용중인 9%Ni강과 STS강, 최근에 개발된 고Mn강을 이용하여 STS 파이프와 접합되어서 이재 용접부에서 발생하는 용접잔류응력을 실험적 및 해석적 검토를 실시하고, LNG의 하역과정을 모사하는 FEM 해석을 실시하여 실제 선박수명 동안 발생 가능한 이재 접합부에서의 응력의 변화거동을 검토하였다.