Electrochemical Characteristics of Delta Ferrite in Thermally Aged Austenitic Stainless Steel Weld

An austenitic stainless steel Type 316L weld was thermally aged for 20,000 h at 400 degrees C and electrochemical characterization was performed to measure corrosion resistance in delta-ferrite phase. It is well known that a severe thermal aging causes decrease of fracture resistance and increase of the hardness of delta-ferrite, which was related to the spinodal decomposition. After thermal aging, the DL-EPR response of 316L weld was dominated by parent austenite matrix without reactivation peak. To characterize the delta-ferrite only, austenite phase was selectively dissolved from the matrix by electrochemical etching method. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) analysis of the delta-ferrite phase showed degradation in corrosion resistance after thermal aging with the appearance of a cathodic loop and reactivation peak during the reverse scan. The degradation in corrosion resistance of delta-ferrite phase could be attributed to the localized Cr-depletion due to spinodal decomposition and precipitation of inter-metallic phases during thermal aging.