This paper concerns the study of aging mechanism of welded joints of P92 steels. Alloys like P92 steel are commonly used in ultra-supercritical (USC) power plants. Depending on the service conditions, the welded joints may become a critical weak link between component connections, showing crack openings and even failures. In this study, the long-term aging effect on the welded joints of P92 steels was investigated under the expected service temperature of 650°C. Microscopic analysis showed that under normal heat treatment, a weld joint has martensitic micro-structure with carbide particles of size 0.1∼0.2μm distributed along grain boundaries. After aging 1000h, white deposits are seen to precipitate from the grain and lath boundaries. Further aging makes these deposits to grow bigger and denser. After 7000h, the Laves phase may grow up to 1μm, causing the material to weaken and fail.

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