Abstract
Microstructure characterization and impact toughness test were performed on the P92 steel weld metal which was sectioned from the component of the main steam pipe of an ultra- supercritical unit after 8000 h exposure at high temperature. Precipitates of M₂₃C₆, MX, and Laves phase were detected in the weld metal. The weld metal after long-term service possessed much lower impact toughness compared with the as-fabricated weld metal. Micro-cracks were also found in the weld metal which formed during the welding process. Impact toughness reduction in the weld metal was correlated with the microstructure evolution.

Key words
P92 steel, weld metal, microstructure, impact toughness, precipitates

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