Microcrystallographical Characterization of Initiation of Intergranular Stress Corrosion Cracking on Alloy 600 in Terms of Local Stress at Grain Boundary Induced by Slip Deformation

Abstract

The initiation of intergranular stress corrosion cracking (IGSCC) on Alloy 600 in a simulated pressurized water reactor primary water environment was investigated by the characterization using an electron back scattering diffraction (EBSD) on flat tensile specimens subjected to a slow strain rate testing. The IGSCC initiation was evaluated for many grain boundaries in terms of the grain boundary characteristics and the local stress generated at each grain boundary; the latter is estimated by considering the specific slip deformation determined by the Schmid factor of two grains adjacent to a grain boundary. This simplified local stress evaluation for IGSCC susceptibility based on EBSD analysis is introduced for the first time in this study. IGSCC tends to occur as a result of induced tensile stress rather than shear stress at the grain boundary, whereas no IGSCC occurred when compressive stress was applied at the grain boundary. Similar results were observed for both 10% and 20% cold worked (CW) specimens in the stress analysis. It was noted that crack initiation depends not only on the stress at the grain boundary but also on the strain concentrated around the grain boundary for the 20% CW specimen.