Avaliação da compatibilidade metalúrgica e da resistência à corrosão de revestimentos da liga AWS ER NiCrMo-4 aplicados por soldagem SAW sobre o aço API 5L Gr B.

Abstract

The aim of this study was to evaluate (C-276) nickel superalloy weld overlays applied by Submerged Arc Welding (SAW) process using different welding parameters, onto API 5L Gr B steel used in the Oil and Gas Industry. AWS ER NiCrMo-4 wire with 1.13 mm-diameter and an agglomerated, fluoride basic, non-alloying flux were used as consumable, and segments of API 5L Gr B steel pipe with 18 mm thickness and 290 mm internal diameter was used as substrate. Initially, it was used two-level factorial design techniques to obtain isolated welding beads. The first factorial design was used for pulsed and second factorial design was employed for conventional current (constant). Subsequent steps consisted of obtaining weld overlays with three bead welds on pipe segments - obtained with rectilinear movement of the welding torch and static substrate - and internal weld overlays also with three bead welds. However, these internal weld overlays were applied into the pipe, with pipe rotating and static welding torch. Then, weld overlays were characterized by optical and electron microscopy, microhardness testing, chemical testing, residual stress and corrosion resistance tests. Using pulsed current the lowest values obtained of dilution and height / width ratio were 3.6% and 0.23, respectively. Using the conventional current these results were 9.62% and 0.21, respectively. The results also indicated that all the weld overlays contained Partially Diluted Zones (PDZ) with hardness above 350HV at the interface weld overlay/substrate. Moreover, weld overlays applied with conventional current presented more PDZ compared to those obtained by pulsed current. The weld overlays applied into the pipe (substrate) rotating - internal weld overlays - showed less PDZ compared to those applied on the static substrate. It was also noted that an increase in the Contact Tip to Work Distance (CTWD) provided a reduction in the welding current that resulted in lower levels of dilution, percentage of Fe and secondary phases rich in Mo and W. All the weld overlays showed compressive stresses and there was a tendency of the stresses to become more compressive by reducing the welding current. The weld overlay that showed the best corrosion resistance also presented the lowest levels of dilution, Fe content, less intermetallic phases rich in molybdenum and tungsten, and the highest Ni, Mo and Cr contents.