600 合金のPWR 一次系水中で形成される酸化皮膜と応力腐食割れ初生に及ぼす溶存水素濃度の影響
This study focused on an initial stage of PWSCC, observed and considered the oxide layer on alloy 600 using three-point bending specimens immersed in 360 °C・30 ml/kg DH and 345 °C・15 ml/kg DH. Crevasses of oxide film along grain boundaries were observed on their surfaces. These conditions are close to chemical equilibrium boundary of Ni/NiO, inhibit the growth of the oxide film on grain boundaries due to lack of oxidizable-Ni and Cr. There is a possibility that their material surfaces in vicinity of grain boundaries weren't covered with oxide film and were contacted with these test water conditions while a long immersing term. The authors reported that the DH concentration dependency of PWSCC initiation by high pre-strained RUB specimen coincided with it of PWSCC crack growth rate by CT specimen. There is a possibility that the coincidence is based on the above mechanism; "less oxide film on grain boundaries" under the condition applied high stress to a surface of SCC test specimen.