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 °C and electrochemical characterization was performed to measure corrosion resistance in δ–ferrite phase. It is well known that a severe thermal aging causes decrease of fracture resistance and increase of the hardness of δ–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 δ–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 δ–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 δ–ferrite phase could be attributed to the localized Cr-depletion due to spinodal decomposition and precipitation of intermetallic phases during thermal aging.
KeywordsDL-EPR analysis Stainless steel weld Thermal aging Corrosion Delta ferrite
This study is mainly supported by the Korea Hydro and Nuclear Power Co., Ltd. as the Proactive Material Aging Management Project. Part of the funding is provided as Nuclear R&D Program (2015M2A8A2074798) of the MSIP/NRF of Rep. of Korea. Financial support for three of the authors is provided by the BK-Plus Program of the MSIP of Rep. of Korea.
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