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An American Welding Society (AWS) E7016 type C-Mn electrode and an AWS E7018 type C-Mn-Ni electrode were each used to produce a series of butt welds in 25-mm (1-in.) thick British Standard (BS) 4360 50E (C-Mn-Nb) steel plate in the flat (1G) position. For each consumable, direct current (DC) reverse polarity (electrode positive), DC straight polarity (electrode negative), and AC power supplies were each used for a complete panel. In addition, DC straight polarity was employed for vertical-up (3G) welding with the C-Mn-Ni electrode. The chemical composition, strength, microstructure, and toughness of the deposits were studied in the as-welded condition.
For the C-Mn-Ni 1G welds (and to a lesser extent for the C-Mn welds), manganese and silicon decreased in the order DC reverse polarity, AC and DC straight polarity. For both consumables, there was a concomitant increase in nitrogen content. There were no associated changes in strength or microstructure, but there was generally a progressive decrease in crack tip opening displacement (CTOD), measured at - 10°C, and in Charpy toughness. As a consequence of strain aging, Charpy toughness was lower in the root than in the fill region.
The 3G DC straight polarity C-Mn-Ni deposit had higher strength in the root and higher Charpy toughness than the corresponding 1G deposit. The CTOD of the former was lower and showed much more scatter, to which locally low toughness regions (revealed by fractographic examination) contributed.
carbon-manganese steels, shielded metal arc welding, vertical-up welding, polarity, AC, DC, weld metal, composition, oxygen, nitrogen, microstructure, strength, impact toughness, fracture toughness, CTOD
Principal research metallurgist, The Welding Institute, Cambridge,