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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.
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.
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.
신구용(Koo-Yong Shin),노희원(Hee-Won Nho),최진성(Jin-Seong Choi),오장만(Jang-Man Oh),방항권(Hang-Kweon Pang),신태우(Tae-Woo Shin),이동일(Dong-Il Lee) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
국내의 송전선 지지물 설계는 전기설비기술기준과 한국전력공사 송전설계기준에 근거하여 적용되며, 철탑하중에 큰 비중을 갖는 풍하중기준은 1985년 기상청의 풍속 데이터를 반영하여 1987년경에 제정된 지침을 지금까지 적용하고 있다. 당시 제정된 설계기준에서는 지역별 풍속 차이에 따라 Ⅰ, Ⅱ, Ⅲ, 지역 및 울릉도로 구분하여 차등 적용하는 설계개념으로 주변여건을 고려하지 않고 동일한 지역내에 위치하고 있는 송전지지물의 경우에는 동일한 풍하중을 적용하는 방식이다. 최근 해외 철탑설계기준과 국내 건축물 설계기준에서는 전산기술의 발달로 국부적인 지형영향을 고려하여 철탑별로 개별적인 풍하중을 산정하는 방식을 채택하고 있다. 본 논문에서는 상용 송전선로 설계가 진행되고 있는 군산-새만금 예정 경과지 가운데 지형조건을 고려한 풍속할 증이 요구되는 개소에 대한 설계 풍하중 검토사례를 소개한다.
스테인리스강 STS 316L과 탄소강 A516-70의 이종금속 GTA 용접부 특성에 대한 연구
김세철(Se Cheol Kim),신태우(Tae Woo Shin),문인준(In Joon Moon),장복수(Bok Su Jang),고진현(Jin Hyun Koh) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.4
Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of δ-ferrite was increased with increasing heat input due to the increase of Creq /Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.
듀플렉스 스테인리스강(ASTM A240 UNS S31803)의 FCA 용접 후 열처리가 용접부 특성에 미치는 영향
현준혁(Jun-Hyeok Hyun),신태우(Tae-Woo Shin),장복수(Bok-Su Jang),김상호(Sang-Ho Kim),고진현(Jin-Hyun Koh) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
The effect of post-weld heat treatment(PWHT) on microstructure, mechanical properties and pitting corrosion resistance of UNS S31803, duplex stainless steel(DSS), weld metals was investigated. Three heat inputs of 7.6, 12.5, 18.0kJ/cm were employed to make joints of DSS with E2209T1-1/4 wire and PWHT was conducted in three temperatures of 1070, 1100, 1130℃. Microstructure in weld metals after PWHT consisted of allotriomorphic rather than needle-shaped austenite. Secondary austenite was scarcely formed and intermetallic compounds were not formed. Ferrite content was increased with increasing PWHT temperatures because δ-ferrite was stable phase and ferrite can not be sufficiently transformed to austenite due to rapid cooling. The difference of Cr, Mo and Ni contents between δ-ferrite and austenite after PWHT increased compared to that before PWHT. Hardness of weld metals became lower than that of base metal after PWHT. Also, hardness of weld metals was increased while impact absorbed energy was decreased with increasing PWHT temperature because of increase of δ-ferrite content. In pitting corrosion test, the critical pitting corrosion temperature(CPT) after PWHT increased by approximately 10℃, and CPT of weld metals was between 35 and 40℃. Heat-treated specimens in 1070℃ was corroded in base metal because ferrite content of base metal was quite high over 60%.