The influence of the shielding gas composition on GMA welding of ASTM A 516 steel

Abstract

The gas metal arc welding process has wide industrial applications; however, its use in the production of pressure vessels has been limited, because the welds produced do not comply with the requisites imposed by the standards that govern construction of these pieces of equipment. This work was intended to study the influence of shielding gas mixtures on ASTM A 516 grade 70 steel. Three different gas mixtures were used containing varying levels of argon, helium, carbon dioxide and oxygen. As a first step, weld beads were deposited on plates with the gas mixtures tested and morphological analyses were made of the welds obtained. Multi-pass welds were then made on joints with a ‘V’-shaped groove, for cryogenic Charpy tests. Study of the morphology of the weld beads showed that an increase in the helium gas caused greater fusion around the edges of the beads, to the detriment of penetration. The results of the Charpy test showed the best results for the mixtures that contained helium. However, oxide inclusions were seen in the samples tested, with fewer inclusions in welds produced with the helium mixtures. The higher incidences of inclusions point to a direct relationship with the lowest values of energy absorbed.