AbstractThe microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time–temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr–1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy carbide formation at the expense of cementite.MST/1895