Microstructural stability and creep rupture strength of the martensitic steel P92 for advanced power plant

Japanese 9% Cr steel containing 0.5% Mo and 1.8% W (P92) has been investigated. Quantitative microstructural analyses using TEM of thin foils and extraction double replicas have been carried out after different austenitization and tempering treatments and after creep deformation at 600 and 650 degrees C. Statistical quantitative analyses were undertaken to determine the dislocation density within the martensite laths, the width of the martensite laths/subgrains and the size and distribution of the carbide and carbonitride precipitates. Correlation of the results of the microstructural investigation with the creep rupture properties allowed the stability of the microstructure during the high temperature exposure to be assessed. The consequences of microstructural changes for the extrapolation of creep rupture data to design lifetimes are considered. Taking into account the strengthening mechanisms which remain effective in long term testing, the 100000 h stress rupture strength of P92 at 600 degrees C: is estimated at 115 MPa. (C) 1997 Acta Metallurgica Inc.