1999 Volume 48 Issue 2 Pages 74-81
To clarify the acidic Intergranular Stress Corrosion Cracking (IGSCC) mechanism of alloy 600, some metallurgical factors were extracted from the various IGSCC contributing factors, and several kinds of experimental studies were conducted. Acidic IGSCC susceptibilities of mill-annealed, sensitized and thermally treated (TT) alloy 600 which have different grain boundary characteristics were examined using C-ring and SSRT tests. Grain boundary characteristics, such as chromium depletion, intergranular slipping behavior and electrochemical dissolution, were examined in detail using a modified Huey test, a Transmission Electron Microscope (TEM) study, and an electrochemical measurement, respectively. The C-ring and SSRT results showed that the IGSCC resistance of the sensitized material which had the chromium depletion zone was the least, and the TT material was the most resistant. TEM analysis showed that the slips at the grain boundary were easy to detect in the mill-annealed and sensitized materials. In the TT materials, however, slips were suppressed by its intricate dislocation morphology. Electrochemical study showed that the preferential dissolution of nickel tended to occur with an increase in temperature and decrease in pH under the acidic condition. From these metallurgical and electrochemical test results, it was concluded that the slipping behavior and the nickel dissolution at the chromium depletion zone worked together as the influencing factor to acidic IGSCC.
