Sensitization and pitting corrosion resistance of ferritic stainless steel aged at 800°C

This work investigates the influence of sensitization conditions on pitting corrosion resistance of ferritic stainless steel UNS S43000 aged at 800 degrees C between 10 min and 320 min. UNS S43000 steel is susceptible to intergranular corrosion after solution treatment at 1,160 degrees C followed by water-quenching, as a consequence of the chromium depletion of the grain boundaries adjacent areas, due to chromium carbide precipitation during cooling. Isothermal treatments of 10 min at 800 degrees C decrease the sensitization degree, and intergranular corrosion resistance is recovered after 20 min at 800 degrees C. The solution-treated specimens have a high pitting potential in 3.5% sodium chloride (NaCl) solution compared to the same material treated at 800 degrees C for 10 min. The resistance to pitting corrosion is reduced by chromium depletion associated with an increase of inter- and introgranular precipitation of chromium carbide. For treatments longer than 20 min at 800 degrees C, the pitting corrosion resistance returns to the high level observed for the solution-treated condition, as a consequence of chromium redistribution that occurs after 20 min at 800 degrees C. The scan rate used in potentiodynamic tests plays a minor role on the pitting potential, while a rougher surface leads to lower pitting potentials in all studied conditions.