Damage evaluation of type 304 and 316LN stainless steel structure under creep-fatigue loading

In this study high temperature structural test was carried out in sodium coolant environments and microstructural observation as well as material strength tests were performed to evaluate the damage under structural test. The creep-fatigue load with one period of 3 hours was applied 1055 times over the temperature range of 250 deg C to 600 deg C for the structural test. An investigation of the damage distribution by microscopic images showed that the 316LN specimen was less damaged than the 304SS during the structural test. The results of material strength test with material specimens sampled along the thickness direction in structural model showed that the fatigue strength of 304 and 316LN stainless steels were almost the same with those of the mean fatigue strength curve for the undamaged materials. This means that the structural test model was nearly undamaged during the structural test, and the results are in agreement with those of microscopic observations