High-cycle fatigue properties of modified 316 stainless steels under in situ thermal-pulses

To get an insight into high cycle fatigue (HCF) properties of austenitic st ainless steel under fusion reactor operation conditions, we carried out the epsilon (p)-controlled HCF tests at 403 K and those under in situ thermal pulses (TP-tests) for a low-carbon and high-silicon 316L, stainless steel, where epsilon (p) is the plastic strain amplitude. The surface morphology o f slip bands observed for the specimens subjected to HCF strains is similar to that of the persistent slip bands (PSBs) in copper. However, applicatio n of the traditional method employed for the confirmation of PSBs in copper to the present specimens indicates that the slip bands observed at the ear ly quarter of the fatigue life, N-f are composed of PSBs as the major fract ion and suspended slip bands as the minor fraction. After the slip band obs ervation, we surmise that the elongation in N-f reported for the TP-tests w ith a temperature jump DeltaT of about 10 K at about 333 K is associated wi th revival of the suspended slip bands. On the other hand, we found here th e shortening in hi for the TP-tests with dr of 16 to 32 K at 403 K as well as that reported for the TP-tests with DeltaT of about 100 K at about 333 K reported, suggesting that the constituent plastic strain per PSB increased after Tps. We surmise that fine fatigue-induced defects are formed in PSBs at around 403 K and work as obstacles against dislocation motions in PSB. The present work demonstrates that for the structural material subjected to the HCF strains, the shortening in N-f can be expected under in situ TP co ndition as well as under in situ irradiation condition reported.