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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.
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.
슈퍼듀플렉스 스테인리스강 UNS S32750과 탄소강 A516-70의 이종금속 FCA 용접 특성에 대한 연구
문인준,장복수,김세철,고진현,Moon, In-June,Jang, Bok-Su,Kim, Se-Cheol,Koh, Jin-Hyun 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.4
The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.
슈퍼 듀플렉스 스테인리스강 UNS S32750의 FCA 용접 후 열처리가 공식에 미치는 영향
장복수,문인준,김세철,고진현,Jang, Bok-Su,Moon, In-June,Kim, Se-Cheol,Koh, Jin-Hyun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.5
This study was carried out to investigate the influence of a sigma phase precipitation on the pitting corrosion resistance and microstructural change of super duplex stainless steels(UNS S32750). The welds made by FCAW (Flux Cored Arc Welding) were heat treated ($930^{\circ}C$, $1080^{\circ}C$, $1230^{\circ}C$) and quenched. Based on the microstructural examination, it was found that the ${\sigma}$ phase was formed in base metals and welds heat treated at $930^{\circ}C$ while there were little ${\sigma}$phases formed in base metals and weld metal experienced the relatively fast cooling from $1080^{\circ}C$ and $1230^{\circ}C$. On the other hand, the most weight loss due to pitting corrosion occurred in base and weld metals heat treated at $930^{\circ}C$. It was confirmed that the pitting corrosion occurred in the phase boundaries of ferrite/sigma and austenite/sigma. The pitting corrosion resistance decreased owing to an increase in Cr, Mo depleted areas adjacent to the intermetallic phases such as ${\sigma}$phases. The hardness was greatly increased due to the precipitation ${\sigma}$phases.