SUS 316鋼の高温高圧純水中の粒界応力腐食割れにおけるMoの役割

抄録

Effects of solution treatment temperature and sensitization time on stress corrosion cracking (SCC) have been studies on SUS316 stainless steel in high temperature pure water at 562K containing dissolved oxygen of 8 ppm using a slow strain rate testing (SSRT) technique at 4.17x10^-6s^-1 and 8.35×10^-7s^-1. The Strauss test (ASTM A262E) and the oxalic acid etching test (ASTM A262A) were used to determine the degree of sensitization and Huey test (ASTM A262C) and anodic polarization test were used to determine the influence of step solution treatment on segregation of impurities at grain boundary.
The specimens which were solution-treated at 1373K, had more precipitates of M₂₃C₆ and Laves phases than those at 1573K. For the width of attacked grain boundaries, this trend was coincident. In high temperature water, intergranular corrosion occurred owing to Cr depletion resulting from the precipitation of M₂₃C₆ and Laves phase at grain boundaries of sensitized specimens and then IGSCC occurred at these attacked grain boundaries at low strain and load. IGSCC changed to TGSCC according to the increase of strain.