Study on the Mechanism of Intergranular Stress Corrosion Cracking of Alloy 600 in High Temperature Acidic Solution

摘要

To clarify the acidic Intergranular Stress CorrosionCracking (IGSCC) mechanism of alloy 600, some metallurgicalfactors were extracted from the various IGSCC contributingfactors, and several kinds of experimental studies were conducted.Acidic IGSCC susceptibilities of mill-annealed, sensitized andthermally treated (TT) alloy 600 which have different grainboundary characteristics were examined using C-ring and SSRTtests. Grain boundary characteristics, such as chromium depletion,intergranular slipping behavior and electrochemical dissolution,were examined in detail using a modified Huey test, aTransmission Electron Microscope (TEM) study, and anelectrochemical measurement, respectively. The C-ring and SSRTresults showed that the IGSCC resistance of the sensitized materialwhich had the chromium depletion zone was the least, and the TTmaterial was the most resistant. TEM analysis showed that theslips at the grain boundary were easy to detect in the mill-annealedand sensitized materials. In the TT materials, however, slips weresuppressed by its interacted dislocation morphology.Electrochemical study showed that the preferential dissolution ofnickel tended to occur with an increase in temperature anddecrease in pH under the acidic condition. From thesemetallurgical and electrochemical test results, it was concludedthat the slipping behavior and the nickel dissolution at thechromium depletion zone worked together as the influencingfactor to acidic IGSCC.