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용접 자세에 따른 해양구조물용 항복강도 420MPa급 고강도강 FCA 용접부 파괴인성에 대한 연구
김인찬(In-Chan Kim),정상훈(Sang-Hoon Jeong),최한글(Han-Geul Choi),김명현(Myung-Hyun Kim) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.2
The fracture toughness of flux cored arc weld metal with the yield strength 420MPa grade high strength steels for offshore structures depending on the welding position was investigated. Charpy V-notch impact test and the CTOD test of the weld metal in the horizontal and the vertical-up welding positions were carried out, and the microstructure and M-A constituents of the weld metals were observed. The recovery rate of alloying elements in horizontal position weld metal were higher than vertical-up position weld metal and the fraction of low temperature transformation phases having high dislocation density in the horizontal position weld metal was high. As a result, the yield strength, tensile strength and impact toughness of horizontal weld metal were higher than those of vertical-up position weld metal. On the other hand, the CTOD value of vertical-up position weld metal was much higher than horizontal position weld metal. This is because the M-A constituents transformation is promoted by the post-welding on the low temperature transformation region having a high local C concentration in the horizontal position welding, and therefore, the breakdown starts easily by the high M-A constituents.