A Study On Correlation Of Microstructural Degradation And Mechanical Properties Of 9-12%Cr-Steel For Ultra-Super Critical Power Generation

For the good combination of high-temperature strength, toughness and creep property, 9-12% chromium steels are often used for gas turbine compressors, steam turbine rotors, blade and casing. In this study, the correlation of microstructural evolution and mechanical properties was investigated for the specimens heat-treated at 600, 650 and 700 degrees C for 1000, 3000 and 5000 hrs. The microstructure of as-received specimen was tempered martensite with a high dislocation density, small sub-grains and fine secondary phase such as M23C6. Aging for long-time at high temperature caused the growth of martensite lath and the decrease of dislocation density resulting in the decrease in strength. However, the evolution of secondary phases had influence on hardness, yield strength and impact property. In the group A specimen aged at 600 degrees C and 650 degrees C, Laves phase was observed. The Laves phase caused the increase of the hardness and the decrease of the impact property. In addition, the abrupt growth of secondary phases caused decrease of the impact property in both A and B group specimens.