Requirements for microstructural investigations of steels used in modern power plants

The thermo-mechanical behaviour of newly developed 9-12 wt.% Cr steels used in steam power plants depends strongly on the microstructure. In the present work, a combination of various microscopy techniques is used to study the microstructural features relevant for the creep resistance. These include the subgrain size, the number of free dislocations, the chemical composition and crystallographic structure of the occurring precipitates, and their density and size distribution. Accordingly, the techniques which were applied range from light microscopy to transmission electron microscopy in order to cover all lengthscales from the millimeter regime to the nanometer level. These detailed investigations are important for alloy design and as input parameters for thermodynamical calculations and modelling of the microstructural evolution to develop steels for cleaner power stations with high thermal efficiency.