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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%.
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.
알루미늄 합금 AA6061-T6와 Silafont-36의 이종금속 레이저 용접부 특성에 관한 연구
현준혁(Jun-Hyeok Hyun),신태우(Tae-Woo Shin),장복수(Bok-Su Jang),김상호(Sang-Ho Kim),고건호(Gun-Ho Go),김태영(Tae-Young Kim),고진현(Jin-Hyun Koh) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.5
The characteristics of dissimilar weld metals between AA6061-T6 and Silafont-36 by laser welding were evaluated in terms of bead shape, microstructure, EDS analysis, hardness, and tensile strength. Laser power of 3.0, 3.5, 4.0kW and incident angle of 15, 20° were employed to make dissimilar weld metals. Bead shape of weld metal with 3.5kW, 15° was most stable. Microstructure of dissimilar weld metals consisted of columnar dendrite in area adjacent to fusion line and equiaxed dendrite in center of weld metal. Also, Mg2Si and α-AlFeMnSi were precipitated in weld metal. Microstructure in HAZ of Silafont-36 consisted of eutectic Al-Si, Mg2Si, and β-Al5FeSi. Si contents of weld metal made with 4.0kW, 15° were very high. And Mg contents of weld metals were relatively low because of vaporation of Mg. Hardness of weld metal made with 4.0kW, 15° was very high because Si contents of that were high. In tensile test, Specimens were fractured in Silafont-36 or weld metals. The fracture in base metals was due to low tensile strength of Silafont-36, and the fracture in weld metals was due to undercut or porosity.
스테인리스강(ASTM Type 316L)과 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성에 대한 연구
김세철(Se Cheol Kim),현준혁(Jun Hyeok Hyun),신태우(Tae Woo Shin),고진현(Jin Hyun Koh) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.3
Characteristics of dissimilar metal welds between ASTM Type 316L and carbon steel ASTM A516 Gr.70 made with FCAW were evaluated in terms of microstructure, ferrite content, EDS analysis, hardness, tensile strength, impact toughness and corrosion resistance. Three heat inputs of 10.4, 16.9, 23.4kJ/cm were employed to make joints of dissimilar metals with E309LMoT1-1 wire. Microstructure of dissimilar weld metals consisted of mostly vermicular type of δ-ferrite and some lathy type of δ-ferrite, and δ-ferrite was transformed into globular type in reheated zone. In all conditions, weld metals were solidified on FA solidification mode. Based on the EDS analysis of weld metals, All Creq/Nieq values were in the range of FA solidification mode, and it was decreased with increasing heat inputs whereas it was increased with increasing layers. The amount of δ-ferrite was decreased with increasing heat input due to the difference of cooling rate, and it was increased with increasing layers. Accordingly, hardness and tensile strength of dissimilar metals weld joints was decreased with increasing heat input while impact energy was increased with increasing heat input. Corrosion test of dissimilar metals weld joints showed that weight gain rate of heat input 10.4kJ/cm was the greatest, and that of three heat inputs became constant after certain time.
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.