Creep fracture behavior of [formula omitted]Cr1Mo welds from a 31-year-old fossil power plant

Abstract

Both creep deformation and creep crack growth experiments have been conducted on ex-service 2 1 4 Cr−1 Mo welds. A creep rate ϵ · equation, ϵ · = 9.5 × 10 −2σ 9.36 (−Q/RT), where Q is the creep activation energy of 337.5 kJ mol −1, R is the gas constant and T is the test temperature, has been derived. The predicted ϵ · values using the above equation were found to be in good agreement with the experimentally measured values. The rate-controlling process of creep deformation of the present 2 1 4 Cr−1 Mo welds is suggested to be related to the mechanism of dislocation climb. The new correlating parameter C t for time-dependent crack growth developed by Saxena can be used to characterize the creep crack growth behavior of 2 1 4 Cr−1 Mo welds. The creep crack growth rate d a/d t properties can be described by the equation d a/d t = 8.38 × 10 −5 C t 0.77. Dimpled fracture mixed with cavities was observed on the fracture surfaces of both creep deformation and creep crack growth tested specimens, regardless of applied load level or test temperature. Moreover, during creep tests, a majority of cavitation was observed to initiate at the carbides along the grain boundary. The weld metal was found to demonstrate greater creep deformation rates and faster creep crack propagation rates than the corresponding base metals. The degraded creep properties of the present ex-service weld metal were suggested to be related to the existence of agglomerated intergranular carbides which could facilitate cavitation.