In this paper, the microstructure of 9%Cr steel 10Cr9MoW2VNbBN under different heat treatment or creep testing was investigated. The morphology of tempered martensite microstructure varies after different heat treatment. After the creep test at 620°C or 650°C, the martensite lath microstructure kept unchanged, although the amounts and the sizes of precipitates, such as the carbides M23C6, carbonitrides MX, and Laves phase, increased with the creep time. The martensite laths microstructure morphology changed after the creep test at 700°C, with the carbides coarsened severely at grain boundaries.
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