Cr-segregation by spinodal decomposition and G-phase precipitation were observed in δ-ferrite of austenitic stainless steel welds thermally aged at 400 °C for up to 20,000 h. A reversion heat treatment (R-HT) at 550 °C for 1 h dissolved the Cr-segregation in the aged welds while some intermetallic precipitates were present. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) analysis showed no significant differences among them. However, after selective etching of the austenite phase, the DL-EPR values of δ-ferrite phase steadily increased with aging time due to the growth of Cr-depleted regions by spinodal decomposition. The electrochemical behavior of δ-ferrite after R-HT condition was similar to that of unaged welds, indicating the intermetallic precipitates did not affect the corrosion resistance in this case. Overall, DL-EPR analysis of δ-ferrite phase provided better correlation with spinodal decomposition.
Bibliographical noteFunding Information:
This study was mainly supported by the Korea Hydro and Nuclear Power Co., Ltd. as the Proactive Material Aging Management Project. Part of the funding was provided as Nuclear R&D Program (2015M2A8A2074798) of the MS&ICT/NRF of Rep. of Korea. Financial support for two of the authors was provided by the BK-Plus Program of the MS&ICT of Rep. of Korea.
© 2018, The Author(s).
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