SCC initiation behavior of one mill annealed alloy 600 plate heat was investigated in simulated PWR primary water under constant load at yield stress with in-situ direct current potential drop (DCPD) monitoring for crack initiation. Twelve specimens were tested at similar cold work levels among which three showed much shorter SCC initiation times (1200 hrs). Post-test examinations revealed that these three specimens all feature an inhomogeneous microstructure where the primary crack always nucleated along the boundary of large elongated grains protruding normally into the gauge. In contrast, such microstructure was either not observed or did not extend deep enough into the gauge in the other specimens exhibiting ~3-6X longer initiation times. In order to better understand the role of this microstructural inhomogeneity in SCC initiation, high-resolution microscopy was performed to compare carbide morphology and strain distribution between the long grains and normal grains, and their potential effects on SCC initiation are discussed in this paper.
Revised: May 31, 2018 |
Published: January 2, 2018
Citation
Zhai Z., M.B. Toloczko, and S.M. Bruemmer. 2018.Microstructural Effects on SCC Initiation PWR Primary Water Cold-Worked Alloy 600. In Proceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors (EDM 2017), edited by JH Jackson, D Paraventi, M Wright, 1, 217-229. Cham:Springer.PNNL-SA-126736.doi:10.1007/978-3-319-67244-1_14