CREEP CAVITATION IN A NICR STEEL

Abstract

Through creep tests at 823 K and intermittent cryogenic separation of grain boundaries of a NiCr steel with well-defined secondary stage creep, the continual cavity nucleation and diffusive growth models based on the linear relation between the cavity number and creep strain were examined. A one-dimensional (1-D) model[1] can predict rupture times within a factor of 2 and their stress exponents accurately and was supported by the stress dependence of the Monkman-Grant product. The area fraction of fully coalesced area (FCA) increased linearly with the density change of specimens and rupture occurred at FCA approximately 0.5. Then, by treating FCA as a damage parameter and applying the Avrami equation, it was shown that the extended area of FCA was proportional to sigma(2n)t3, which led to t(f) approximately sigma(2n/3).