Influence of the Shielding Gas Composition on GMA Welding of the ASTM A516 Steel

The GAMW process has been widely used in the mechanical industry. However in the production of pressure vessels, the use of this process has been limited, because the produced welds do not reach the requirements imposed by the standards that govern the construction of these equipments. This work aims to study the influence of the shielding gases composition in GMAW on the weldability of the ASTM A516 steel degree 70 steel. In this research, three shielding mixtures are proposed, containing varied contents of argon, helium, carbon dioxide and oxygen. Bead-on-plate welds were deposited on steel plates with each composition of shielding mixtures. The study of the morphology of the weld beads showed that the increase of the proportion of helium led to deeper fusion at the borders of the beads. To evaluate the impact resistance of the welds by Charpy tests, joints with V-groove were welded with AWS ER70S-6 filler metal. The best results of charpy tests were obtained when mixtures containing helium were employed The presence of oxide inclusions was observed in the analyzed samples, and the lower oxide inclusions occurrence was observed in the welds deposited with helium containing mixtures. There are evidences to point to a direct relationship between smaller values of absorbed energy and oxide inclusions.