Avaliação de técnicas para mitigar a corrosão na ZAC de união soldada em aço inoxidável ferrítico P410d

Abstract

The heat affected zone (HAZ) is the most susceptible region for corrosion occurrence in a welded joining. Besides microstructural variations, the corrosion susceptibility of HAZ is increased by stresses that act on it (residual ones, related to welding thermal cycles, added to external stresses) and also by stress concentration factors connected to the geometry of the weld edge (toe). Machining (grinding) of the weld edge is used to increase the smoothness (concordance) between the weld bead and the base metal. However, such techniques do not eliminate problems associated to the presence of inclusions, porosity and segregation, which increase corrosion wear. TIG Dressing technique has been used for reducing fatigue crack occurrence from stresses generated in the weld edge. The use of this technique is expected to increase the concordance between weld bead and base metal and to reduce the tensile residual stresses in the surface (tensile stresses increase the HAZ corrosion susceptibility). Therefore, the effect of external stresses concentrated at the concordance between weld bead and base metal on corrosion wear at the weld edge of the HAZ was evaluated. Both machining and TIG Dressing techniques were used to smoothen the concordance. The effects of tensile stresses, superficial finishing and microstructural variations in the HAZ were quantified by the wearing after submitting the samples to chloriteion medium. Wear in MIG/MAG and TIG Dressing HAZ were assessed using optical microscopy by using a mask that reveals the corrosion area in terms of linear dimension of the welded and bended samples. From the obtained results, it was observed that the TIGDressing technique led to lower wear in the HAZ, especially when using pure argon as shielding gas. By using electrochemical measurements, it was observed the HAZ of the weld edge of the bead from TIG Dressing is the most susceptible region for corrosion wear and anodic dissolution occurs.