Yasuhiro Masaki

Effect of Cr and Ni on Stress Corrosion Cracking Susceptibility in Ni-Cr-Fe Alloys Under Simulated Pressurized Water Reactor Primary Conditions

The primary water stress corrosion cracking (PWSCC) susceptibility of Ni-based alloys, such as Alloy 600 (UNS N06600), has been much higher than that of Fe-based alloys, such as Type 316 stainless steel (UNS S31600). This phenomenon is generally recognized; however, the effects of Fe, Ni, and Cr are not fully understood. In this study, the effect of Cr and Ni in Ni-Cr-Fe alloys on PWSCC susceptibility was investigated using alloys with a wide range of Ni content. The role of these elements is discussed from the standpoint of grain boundary oxidation. According to the stress corrosion cracking (SCC) test results, high-Ni alloys with low Cr contents had high SCC susceptibility, and the SCC susceptibility in high Ni-content alloys was improved by increasing Cr content. On the other hand, low Ni-content alloys had low SCC susceptibility, irrespective of Cr content. These features agree with the field experience in pressurized water reactor plants. In comparison with the results of SCC tests and immersion test...

Effect of Thermal Treatment on Stress Corrosion Cracking Susceptibility in Alloy 600 and Type 316 Stainless Steel Under Simulated Pressurized Water Reactor Primary Conditions

Under pressurized water reactor primary conditions, the stress corrosion cracking susceptibility of Alloy 600 (UNS N06600) is improved by chromium carbide precipitation in the grain boundaries. However, the effect of chromium depletion on stress corrosion cracking susceptibility is not completely understood. Type 316 (UNS S31600) stainless steel has minimal stress corrosion cracking susceptibility and cold work increases the stress corrosion cracking susceptibility. This study investigates stress corrosion cracking susceptibilities of Alloy 600 and Type 316 SS, which are thermally treated at a temperature of 700°C. Stress corrosion cracking did not occur in Type 316 SS regardless of the thermal treatment conditions. Alloy 600 has high stress corrosion cracking susceptibility with chromium depletion and chromium carbide precipitation. On the other hand, when chromium carbides are precipitated and chromium depletion is recovered, Alloy 600 has low stress corrosion cracking susceptibility. There are some fin...