Tertiary creep behavior of annealed [formula omitted] Cr-1 Mo steel

Abstract

Under various creep conditions for annealed 2 1 4 Cr-1 Mo steel, nonclassical creep curves that contain two steady-state stages were observed. The transition from the first to second steady-state stage involves a quasi-tertiary (increasing creep rate) stage, thus complicating the definition of tertiary creep. Tertiary creep is important because it is often associated with the formation of gross structural instability (i.e., the formation of cracks, voids, or a neck). The present studies indicated a consistent correlation between the onset of tertiary creep and rupture life was obtained when the end of the second steady-state stage was used as the onset of tertiary creep for the nonclassical curves. The creep strains to the end of the second steady-state stage were similar to those to the end of the secondary stage of the classical curves. These results along with previous work indicate that the creep rate during the second steady-state stage of the nonclassical curves is controlled by the same process that controls creep during the secondary stage of a classical curve.