Abstract
To develop the matched filler metal for the structural materials in Generation IV lead-cooled fast reactor (LFR), the microstructural evolution and mechanical property variation of 9CrSi heat resistant steels deposited metals were investigated both for the as-welded and as-aged (at 550 °C) weld metals. The experimental results indicate two precipitates in the as-welded deposited metals: the bigger M23C6 and the smaller MX. Si facilitates the nucleation of M23C6. The chain-like precipitates (consisting of M23C6) form at the boundaries of prior austenite and martensitic laths in high-Si specimens. They deteriorate not only the strength but also the impact energy. Meanwhile, a few δ ferrites form in high-Si deposited metal deteriorating the impact energy. Precipitates tend to nucleate at the interface between the δ ferrite and the martensite after aging. New types of precipitates (Mo-rich M6X and Laves) with rapid coarsening rate form in as-aged high-Si deposited metals as time increases. Coarse precipitates deteriorate the pinning effect, which causes the recovery of laths and dislocations. Subgrain pinned by M23C6 forms in deposited metals with post-weld heat treatment (PWHT) during aging. The structure hinders the formation of M6X and facilitates the formation of nano-sized MX. Therefore, the mechanical properties of deposited metals with PWHT are stable during long-term (up to 10,000 h) aging treatments.
Published Version
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