Corrosion resistance and galvanic coupling of UNS N08031 base metal, heat-affected zone, and weld metal in phosphoric acid at different temperatures

Abstract

Open-circuit potential tests and potentiodynamic anodic polarization curves have been carried out to obtain information about the electrochemical behavior of a highly alloyed austenitic stainless steel. (UNS N08031) used as base metal (BM), heat-affected zone (HAZ) region, and weld metal (WM). The weld was performed using the gas tungsten arc welding technique (GTAW) with a nickel-based alloy (UNS N06059) as filler metal. The galvanic corrosion generated by the electrical contact between the base metal, the HAZ, and the weld metal was estimated from the polarization diagrams according to the mixed potential theory. The objective of the present work was to study the effect of the solution temperature on the corrosion resistance of the studied materials. These materials were tested in 5.5 Mphosphoric acid (H3PO 4) solution at 25°C, 40°C, 60°C, and 80°C. Results demonstrated that materials passivated spontaneously in the studied solution and their corrosion resistance decreased with temperature. © 2011, NACE International.