Minimization of defects in nickel-based superalloy weld overlay deposited by the GTAW cold wire feed process

Abstract

The objective of the present work was to evaluate the influence of the welding parameters in the formation of defects in weld overlays with nickel-based alloys, and its possible elimination through the correct adjustment of the welding parameters. Coatings were deposited with the nickel-based alloy types Inconel 625, Hastelloy C276 and Inconel 686 on C–Mn steel plates, using GTAW cold wire feed process. The planning of the experiments was accomplished by applying the Taguchi method. The control factors evaluated were the energy technique (ET), the welding heat input (E), the type of alloy (L), the shielding gas (G) and the type of arc oscillation (T). Other parameters were maintained constant, having previously been investigated. The results showed that the arc oscillation type is spiral; although it contributes significantly to reduce the dilution level, it causes a strong instability to the process, resulting in most of the cases in surface defects or defects among passes. The optimum condition to avoid defects among passes was identified by the Taguchi method, which was constituted by the following combination of control factors: 2-2-2-3-3, or by: I energy technique (TE-I); medium heat input level (E_medium); Hastelloy C276 alloy; shielding gas Ar + He; double-8 arc oscillation. The optimum condition for the welding without defects results in high dilution level not being indicated for the welding of resistant coverings to the corrosion.

Keywords:

• GTAW welding
• cold wire
• overlay
• defects
• nickel-based alloy

Acknowledgements

The authors of this work thank the Welding Engineering Laboratory – ENGESOLDA (UFC) for all the infrastructure for carrying out this work. Thanks are also due to PETROBRAS for its collaboration in the development of this work. We also thank CAPES for awarding the grant and the promotional organizations FINEP and CNPq for financial support.