Microstructural development during high temperature creep of 9% Cr steel

The modified 9% Cr steel Type P91 is one of the materials presently employed in power plant pipework components. The detailed microstructural analysis of a trial melt produced by Vı́tkovice Steel, Ostrava is reported in the present work. The microstructural evolution during creep at 873 K was investigated by means of transmission electron microscopy and computer image analysis. Two main microstructural elements of tempered martensite ferritic steels, namely subgrains and secondary phase particles, are studied quantitatively. The influence of stress free ageing and the influence of stress under creep conditions on particle coarsening and subgrain growth is determined.