Small crack property of austenitic stainless steel with artificial corrosion pit in long life regime of fatigue

In order to investigate the fatigue strength in a long life regime of austenitic stainless steel with respect to the stress concentration, rotating bending fatigue tests were performed with pitted specimens (pit specimens). The Type 316NG and Type 304TP steel specimens had some artificial corrosion pits in its center. Further, in order to investigate the existence of a non-propagating crack in austenitic stainless steel, surface observations of the specimens that were not broken at 108 cycles were performed using a replication technique. The results of the observation verified that the fatigue strength of smooth (non-pit) specimens at 108 cycles is the fatigue crack initiation limit for both austenitic stainless steels because non-propagating cracks were not discovered in the surface of the specimens. On the other hand, only the pitted specimens of the Type 316NG steel showed non-propagating cracks; they were discovered at the bottom of the artificial corrosion pits. The initiation and propagation behaviours of the non-propagating crack were explained with the stress concentration factor of the artificial corrosion pits and the stress intensity factor range of the non-propagating crack tip.