Precipitates in 9–12% Cr Steel After Creep Rupture Test and Determination of Life Time Assessment Upon Larson-Miller Parameter

In this study, the crystal structures, morphologies, and compositions of carbides in a 9–12% Cr steel after creep at the temperature range of 593–677 °C, and stress levels of 80–360 MPa had been carefully investigated using scanning electron microscopy, transmission electron microscopy and dispersive X-ray spectrometry. The major types of second phases were M₂₃C₆, Laves phase and MX. After creep rupture test, the M₂₃C₆ carbides in prior austenite grain boundaries and martensite lath boundaries were extensively coarsened. During creep rupture test, Laves phase formed at the grain boundaries and lath boundaries with larger size, and grew faster at higher temperature. For the assessment of the time t (hour) and temperature T(K) on the life time, Larson-Miller parameter P = T(C + log t) is extensively used, which can also be used for the residual life assessment of the 9–12% Cr steel in this study.