X phase and its effect on the mechanical properties of a Mo-bearing high-Si austenitic stainless steel after aging at 650?C

In this study, a Mo-bearing high-Si austenitic stainless steel was designed for lead-cooled fast reactor, and the precipitation behavior and mechanical properties of the experimental steel after 650 degrees C isothermal aging for 3000 h were investigated. The results showed that Mo-enriched x phase was revealed to preferentially precipitate not only at grain bound-aries, but also on the nano-sized secondary MC particles during long-term aging. The secondary MC carbides acted as nucleation sites of x phase particles, leading to lenticular shape composite precipitates. Si can improve the precipitation driving force and was discovered to segregate in the x phase, which indicates that Si can accelerate the formation of x phase during aging. The precipitation of the x phase dramatically reduced the plas-ticity and toughness of the steel, but did less harm to the strength.(c) 2023 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).