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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.
Kim et al. (2018) studied this question.