Análise das condições operacionais de soldagem sobre o espaçamento interdendrítico e velocidade de resfriamento local de superligas de níquel

Abstract

Welding is, undoubtedly, one of the most used and versatile processes nowadays. In the oil industry, for example, it is of fundamental importance that the joining of metallic alloys by welding or the coating to protection in corrosive environments accomplishes requirements in order to succeed in the project. Hence, there are precautions that are required over the process; otherwise, catastrophic results can be obtained. Solidification rate is an essential parameter to be controlled over the welding, due to its strong influence on microsegregation, microstructural changes as grain growth, precipitation of deleterious phases and other features. Therefore, some of those problems can be avoided or minimized by the control of solidification rate. The main objective of this study was to investigate the influence of welding operational conditions on the secondary dendrite arm spacing and its association with the solidification rate in welds of Ni-based superalloys. It was used the Taguchi statistical method to determine the effect of operational conditions. The control factors selected were: shielding gas, filler metal, heat input technique, welding heat input and arc waving. The welds were performed using GTAW cold wire feed process. From the several control factors evaluated, all were statistically significant. There was observed a light influence of the type of alloys, specially concerning the addition of Nb. The increase of heat input has conducted to a reduction in solidification rate. The shielding gases have a profound influence on the conditions of solidification, as well as the arc waving. In general, it was demonstrated that is possible affect the solidification rate by other operational conditions indirectly related to the heat input.