The residual lifetime of creepdeformed material: Microstructural changes occurring during creep of a 12%CrMoVW steel

Abstract

The microstructure of specimens of a 12%CrMoVW steel which were creep tested at 500—650°C for 8000—43 000 h has been investigated. The basic microstructure consisted of tempered martensite and about 1% of δ-ferrite. The fine precipitates ( 0.2 μ,Lm) in the tempered martensite grew up to five times their original size during ageing. The precipitates are probably mainly M₂₃C₆. The size of these carbides, as well as those in the previous austenite grain boundaries, could be related to the Larson—Miller temperature—time parameter corresponding to the ageing.