High-Cycle Fatigue Properties of Modified 316 Stainless Steels under <B> In Situ</B> Thermal-Pulses

Abstract

To get an insight into high cycle fatigue (HCF) properties of austenitic stainless steel under fusion reactor operation conditions, we carried out the e 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 e p is the plastic strain amplitude. The surface morphology of slip bands observed for the specimens subjected to HCF strains is similar to that of the persistent slip bands (PSBs) in copper. However, application of the traditional method employed for the confirmation of PSBs in copper to the present specimens indicates that the slip bands observed at the early quarter of the fatigue life, N f , are composed of PSBs as the major fraction and suspended slip bands as the minor fraction. After the slip band observation, we surmise that the elongation in N f reported for the TP-tests with a temperature jump AT of about 10 K at about 333 K is associated with revival of the suspended slip bands. On the other hand, we found here the shortening in N f for the TP-tests with AT of 16 to 32 K at 403 K as well as that reported for the TP-tests with AT 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 condition as well as under in situ irradiation condition reported.