INTERFACIAL MICROSTRUCTURE AND LOW STRESS, HIGH-TEMPERATURE CREEP OF AN AUSTENITIC STAINLESS-STEEL

The tensile creep properties of a 20 Cr, 30 Ni, Ti stabilised austenitic stainless steel at 800°C have been investigated in relation to its intergranular microstructure. Detailed observations have been made of matrix and interfaciai dislocation structures, grain boundary precipitation and grain boundary migration. The combined evidence is in agreement with a transition from Coble (grain boundary diffusion) dominated creep to power law (dislocation) creep at a stress of ~5 MPa. A threshold stress, below which no creep deformation took place, occurred at ~ 1 MPa. No microstructural evidence was found in support of those models for the threshold stress involving the creation of dislocation loops at grain boundary particles. It is suggested that a model involving grain boundary dislocation by-pass of particles is more relevant. At a more macroscopic level, it was found that the calculated back stress on migrating boundaries due to particle pinning was similar to the observed threshold stress. © 1979.