High temperature helium embrittlement in austenitic stainless steels - correlations between microstructure and mechanical properties

Abstract

The key for the understanding of the effect of helium on the high temperature mechanical properties of a certain material is its microstructure. This paper reports detailed microstructural investigations of different austenitic stainless steels after in-beam creep rupture tests using transmission electron microscopy. The microstructures of the different materials, characterized by precipitates, dislocations, grain size, and helium bubble sizes and densities, are compared and correlated to the degree of helium embrittlement measured by the change of creep rupture times and strains of in-beam tested specimens and of unimplanted controls. Different microstructures result in large differences in the resistance against helium embrittlement which are correlated to differences in helium bubble microstructure. Most important is the influence of precipitates on the nucleation of helium bubbles, especially in grain boundaries.