Methods for making alloy 600 resistant to sensitization and intergranular corrosion

Thermomechanical processing (TMP) and strain annealing were performed on alloy 600. The degree of sensitization (DOS) and susceptibility to intergranular corrosion (IGC) were assessed by electrochemical potentiokinetic reactivation and weight loss tests respectively. The grain boundary character distribution was established by orientation imaging microscopy. It was shown that as the fraction of special boundaries increased with TMP/strain annealing, the DOS and IGC rates decreased drastically. Alloy 600 with fraction of special boundaries above 85% showed only uniform corrosion. The DOS and IGC values indicating resistance to sensitization and IGC and the methods to achieve such values have been highlighted.

► Grain boundary engineering of alloy 600 for 85% special boundaries established. ► Intergranular corrosion resistance of alloy 600 in G28 test improved by thermo-mechanical processing. ► Double loop – electrochemical reactivation test values less than 0.78 shown to correspond to uniform corrosion in G28 test. ► Corrosion rate less than 1.27 mm/y in G28 shown to be due to uniform corrosion. ► Corrosion rates over 1.57 mm/y in G28 shown to be a result of grain dropping.