Creep life evaluation based on hardness method of high-Cr ferritic steels

The softening caused by long-term aging for 10Cr-1.5Mo-VNbN steel was investigated with hardness test at temperature range of 500 to 650 degrees C up to 10(5) hours. The softening caused by creep was also investigated at temperature range of 600 to 650 degrees C under stress of 98 to 294 MPa. The change in hardness during long-term aging was able to be expressed by a simple curve in plotting against Larson-Miller parameter. The Softening was accelerated by the stress larger than 79 MPa. The change in hardness during creep under the stress of sigma (MPa) was correlated with those of long-term aging by plotting against the parameter of log T + log(20 + log t) + 0.000239(sigma = 79) where T is the test temperature (K) and t is the loading time or aging time (h). A method to detect the creep damage and to estimate the residual life was deduced from the above mentioned results.