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합금강(ASTM A387 Gr. 91) - 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성 평가 : Part. 2
신태우(Tae Woo Shin),현준혁(Jun Hyeok Hyun),고진현(Jin Hyun Koh) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.3
Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at 750℃ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and Widmannstӓtten ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.
합금강(ASTM A387 Gr. 91) - 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성 평가
신태우(Tae Woo Shin),장복수(Bok Su Jang),고진현(Jin Hyun Koh) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.3
Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at 750℃ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.
듀플렉스 스테인리스강(ASTM A240 UNS S31803)의 FCA 용접부 특성에 대한 연구
현준혁(Jun Hyeok Hyun),신태우(Tae Woo Shin),김상호(Sang Ho Kim),고진현(Jin Hyun Koh) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.4
Characteristics of duplex stainless steel(DSS) weld metals made with FCAW were evaluated in terms of microstructure, ferrite content, EDS and XRD analysis, hardness, tensile strength, impact toughness and pitting corrosion resistance. Three heat inputs of 7.6, 12.5, 18.0kJ/cm were employed to make joints of DSS with E2209T1-1/4 wire. Microstructure in root zone of weld metals showed primary austenite, secondary austenite and δ-ferrite, and the content of Cr, Mo in secondary austenite was lower than that in primary austenite. Microstructures in cap zone consisted of δ-ferrite and primary austenite. Acicular austenite in heat input 7.6kJ/cm was formed whereas allotriomorphic austenite in heat input 18.0kJ/cm was formed. FN (Ferrite Number) values by WRC-1992 diagram using Creq and Nieq was between 40 and 50. Hardness of weld metals was higher than that of base metal in all heat inputs. Hardness of weld metals in heat input 18.0kJ/cm was generally lower than that of HAZ. Impact absorbed energy of weld metals of heat input 18.0kJ/cm at 0℃ and -40℃ was the highest. In pitting corrosion test, the least amount of pitting corrosion occurred in heat input 12.5kJ/cm. Critical pitting corrosion temperature(CPT) in heat inputs of 7.6, 12.5kJ/cm was 25℃, and that in heat input of 18.0kJ/cm was 20℃ because secondary austenite was largely formed in heat input of 18.0kJ/cm.
박재웅(Jae-Ung Park),신태우(Tai-Woo Shin),최진성(Jin-Sung Choi),최한열(Han-Yeol Choi),민병욱(Byeong-Wook Min) 대한전기학회 2010 전기학회논문지 Vol.59 No.3
345㎸ Incheon Thermal Power Plant Transmission Line Collapse Analysis and Countermeasures. The Typhoon Galmaegi which had been formed in July 15, 2008 diminished into a tropical cyclone and cooled the air above the West Sea. The cooled air colliding with the warm inland air caused a strong whirlwind at some places in the west seaside; the whirlwind battered the 345㎸ Incheon Thermal Power Plant Transmission Line to be collapsed. The resistance of transmission towers against wind pressure, one of the key elements in transmission line engineering, is designed to endure the pressure corresponding to the maximum instantaneous wind speed. Before the above accident happened, no transmission line has ever been collapsed by a whirlwind. So this paper is aimed to analyze causes that collapsed 345㎸ Incheon Thermal Power Plant transmission line and to introduce countermeasures.
민병욱(Byeong-Wook Min),신태우(Tai-Woo Shin),최인혁(In-hyuk Choi),최한열(Han-Yeol Choi),박재웅(Jae-Ung Park),유근양(Kun-Yang Yu) 대한전기학회 2006 대한전기학회 학술대회 논문집 Vol.2006 No.7
Porcelain insulators have generally been used in Korea but polymer insulators which are superior in that they are light weight, explosion proof, impact proof, economical with construction characteristics, have been in use for the 154㎸ transmission line since 1999 following a worldwide trend towards the reduced weight, simplification and compact usage of new material insulators. However there have been approximately 500 cases of forest fires in Korea, so the transmission lines that for the most part pass through mountainous areas have been highly effected and the highly polymerized compound polymer insulator has raised concern about reliability in cases of exposure to forest fires. Therefore for the reliability assessment of the effect of forest fires on polymer insulators, mechanical and electrical characteristics are analyzed by an artificial flare test device and transmission facility surrounding conditions along with forest fire characteristics are surveyed. In addition to this, actual 90 ㎸ energized transmission line was tested with an artificial forest fire and the expanded usage of polymer insulators is presented through the analysis of mechanical and electrical characteristics and physical properties, and a study on the influence of forest fires on polymer insulators.