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극저온용 Al-Mg합금 미그 및 플라즈마-미그 하이브리드 용접부 표면에 형성되는 smut 생성 현상 분석
이희근 ( Hee Keun Lee ),윤태진 ( Tae Jin Yoon ),강정윤 ( Chung Yun Kang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.2
Black deposits (smut) are created on MIG welds in cryogenic Al alloys. The smut should be removed because it ruins the appearance of the end product and affects surface treatments such as painting. It was recently reported that plasma-MIG hybrid (PMH) welding controls the formation of smut duringwelding. In order to determine the reason for this, smut formation using both MIG and PMH welding was investigated through metallurgy and arc phenomena analysis. Smut on MIG welds is a Mg-Al-O amorphous layer that includes nano-sized MgO particles less than 100 nm in diameter and MgO particles 1-2 μm in diameter. Smut on MIG welds is created by large amounts of metal vapor from the arc explosion generated between the welding wire and the weld pool after a short circuit transfer. However, smut on PMH welds is not created owing to the small amount of metal vapor produced from a stable globular transfer rather than a short circuit transfer and arc explosion.(Received April 28, 2015)
내부식용 API 5L X70 다전극 SAW 용접부의 내면 저온인성에 미치는 외면 입열의 영향
안현준,이희근,박용규,은성수,강정윤,An, Hyun-Jun,Lee, Hee-Keun,Park, Young-Gyu,Eun, Seong-Su,Kang, Chung-Yun 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.1
This study aims to investigate the effect of heat input of outside SAW weld on low temperature toughness($-20^{\circ}C$) of inside SAW weld for API 5L X70 with sour gas resistance. As increasing heat input of the outside weld, low temperature toughness of the inside weld was decreased. Especially, in spite of the same heat input, the value of low temperature toughness was fluctuated. On the basis of fracture and microstructure analysis, the low temperature toughness is correlated with the fracture area ratio of shear lips and four kinds of fracture sections. These sections were divided with size and shape of dimple correlated with grain boundary ferrite and cleavage correlated acicular and polygonal ferrite in grain. Therefore, it was seen that these sections were two of final solidification area in the inside weld and the outside weld, no reheated zone and reheated zone in the inside weld. In conclusion, it is thought that the difference of low temperature toughness at the same heat input is due to the fact that each of impact test specimens could have the different microstructure, even though the notch was machined under the error tolerance of 1mm. It is because the final solidification area of the inside weld is very narrow.