INFLUENCE OF PRIOR CYCLIC HARDENING ON HIGH-TEMPERATURE DEFORMATION AND CRACK-GROWTH IN TYPE 316L(N) STAINLESS-STEEL

For power generating equipment subjected to cyclic loading at high tem perature, crack growth could arise from the combinations of fatigue an d creep processes. There is potential for the material to undergo hard ening (or more generally changes of material state) as a consequence o f cyclic loading. Results of an experimental study to examine the infl uence of prior cyclic hardening on subsequent creep deformation are pr esented for type 316L(N) stainless steel at 600 degrees C. Experiments were also carried out to explore creep crack growth at constant load, and crack growth for intermittent cyclic loading. For the as-received material there is substantial primary creep (hardening) at constant l oad, while for the cyclically hardened material at constant load the c reep curves show recovery, and increasing creep rate with increasing t ime. Specimens subjected to prior cyclic hardening were also used for a series of creep and creep-fatigue crack growth tests. These tests de monstrated that there was accelerated crack growth compared to crack g rowth in as-received material.