Absence of dynamic strain aging induced by precipitation in 316 austenitic stainless steel during thermal aging at 750 C

Dynamic strain aging (DSA) has long been seen in the solution-treated austenitic stainless steels, but DSA effect is affected after long-term exposure to high temperature in the fourth-generation nuclear reactors. This study investigated the effect of precipitates on the DSA effect of 316 austenitic stainless steel after accelerated aging at 750 degrees C for 10, 100 and 1000 h, which is used to simulate the long-term microstructural evolution at service temperature. A gradual reduction in the DSA effect is found with an increase in the grain boundary precipitates after aging for 10 and 100 h. The frequency of the interactions between dislocations and grain boundaries de-creases because moving dislocations are blocked by the precipitates formed at the grain boundaries. Meanwhile, the grain boundary precipitates occupy part of the grain boundaries, reducing the probability of dislocation emission from grain boundary. As the aging time prolongs to 1000 h, the newly-formed intragranular sigma phase acts as an obstacle to the dislocation movement, resulting in an increase in waiting time (tw-AG1000). Also, Cr atoms can be drained from mobile dislocation into sigma phase, leading to an increase in the aging time (ta-AG1000) required for pinning the arrested dislocations. As a result, the critical strain for the occurrence of DSA signifi-cantly increases, leading to the absence of DSA phenomenon.