Deformation behavior around grain boundaries for SCC propagation in hardened low-carbon austenitic stainless steel by micro hardness test

Nagashima, Nobuo*; Hayakawa, Masao*; Tsukada, Takashi ; Kaji, Yoshiyuki  ; Miwa, Yukio; Ando, Masami*; Nakata, Kiyotomo*

Stress corrosion cracking (SCC) was found in shroud and PLR piping made of low-carbon austenitic stainless steels in Japanese BWR plants. The intergranular type (IG) SCC propagated in hardened heat affected zones (HAZ) around welds. Strength behavior and local plastic deformation for a low-carbon austenitic stainless steel 316L, cold-rolled at the reductions in area of 10, 30% at room temperature to simulate the hardened HAZ, were measured by a micro-hardness test machine and observed by atomic force microscopy (AFM), respectively. The tensile deformation at yield point (0.2% plastic strain) had given to the work-hardened 316L to simulate the plastic zone at the crack tip. It is suggested that one of the IGSCC propagation mechanisms for 316L was related with the intergranular strength behavior and local plastic deformation around grain boundaries.