Effect of long term thermal aging on SCC susceptibility in austenitic stainless steels

Kaji, Yoshiyuki  ; Aoki, So  ; Kondo, Keietsu  ; Yamamoto, Masahiro 

The influence of long term thermal aging on SCC susceptibility in L-grade austenitic stainless steels (SSs) has been investigated using Creviced Bent Beam (CBB) tests. Test materials were type 304L and 316L SSs, and aging heat treatments were conducted at 288C in air for up to 14000 hours followed by solution-annealing (SA) or 20% cold-working (CW). The evaluation of the SCC initiation susceptibility was conducted by CBB tests in BWR simulated high-temperature water at 288C for 1000 hours. It was revealed by CBB tests that long term aged 304L-SA, 304L-CW, and 316L-SA showed low susceptibility of cracking, whereas long term aged 316L-CW showed high SCC susceptibility. And so far, it is considered that the low temperature sensitization was not the main cause of SCC in long term aged 316L-CW, because the previous TEM/EDX analysis on the long term aged 316L specimen showed no chromium depletion in the vicinity of grain boundaries. Further investigations are in progress from the viewpoint of mechanical properties, cold-rolling texture, microstructure and michrochemistry after the long term thermal aging in order to discuss the factors increasing SCC susceptibility.