Abstract: The thermal aging behavior of an as-rolled 316-type austenitic stainless steel (Fe-17Cr-12Ni-2.6Mo-1.6Mn-0.044C (in wt. %)) was investigated under conditions of 550 °C/0-10,000 h, 600 °C/0-1000 h and 650 °C/0-60 h. It demonstrated that the degree of sensitization (R_a) of thermal-aged samples due to the precipitation of M₂₃C₆ particles at grain boundaries can be measured and quantified by using the double loop electrochemical potentiokinetic reactivation (DLEPR) method. At 550, 600 and 650 °C, the determined R_a values increased with thermal aging time in a fourth-order polynomial relationship. Based on the condition of equal R_a values at 550, 600 and 650 °C, the equivalent acceleration equation between thermal aging temperatures and times was established for predicting the degree of thermal damage of austenitic stainless steels during the long-time service at elevated temperatures. Moreover, since the formation of M₂₃C₆ precipitates led to the severe Cr depletion at GBs and the degradation of passive film, the charge transfer resistance (R_ct) values of the 550 °C/9000 h, 600 °C/1000 h and 650 °C/60 h thermal-aged samples were decreased to 20 % that of the as-received sample.

Key words: Austenitic steels, Microstructural sensitization, Precipitation, Thermal-aged damage, Elevated temperature