CAVITY FORMATION AND LINKAGE DURING CREEP-FATIGUE CRACK PROPAGATION IN NEUTRON IRRADIATED TYPE 316 STAINLESS STEEL.

Recent studies of fatigue and crack propagation have demonstrated that cavity formation may be associated with intergranular carbide precipitates in Type 316 stainless steel at elevated temperatures. Quantitative work by D. J. Michel and H. H. Smith has shown that, when the critical relationship between cavity size and spacing was achieved, cavity linkage was accompanied by an acceleration in crack propagation rate and a change in crack propagation mode. Although the acceleration was observed in annealed, thermally aged 316 stainless steel when a 16 minute tension hold period was included in the fatigue cycle, the results suggested that the conditions necessary for the acceleration might be achieved at shorter hold times for neutron irradiated steels. This paper briefly describes the results from an experiment conducted with neutron irradiated Type 316 stainless steel where cavity formation has influenced the creep-fatigue crack propagation rate.