A three-dimensional model of non-slipping stress corrosion cracking under low loads

Abstract

Stress corrosion cracking (SCC) of 316L single-crystal austenitic stainless steel subjected to low loads (σnom = 20-40 MPa) in a 45 % boiling MgCl2 solution was studied using synchrotron X-ray computed tomography, finite element analysis and so on. Results show that there was no surface slip band around the nucleation sites and the tips of short cracks. Three-dimensional reconstruction of discontinuous zig-zag surface SCC crack indicates that the crack was continuous inside the specimen. The obtaining through two-surface trace analysis manifests, rather than {1 1 1} slip planes, the cracks extended along {1 0 0} planes with the lowest surface energy. It is considered that microcleavage and local dissolution synergistically led to the SCC advance, and microshear was also one of the primarily microscopic SCC mechanisms under the high load. The three-dimensional SCC model was created at the low stress level, where a main SCC crack grew along the MPD due to anodic dissolution, and a microdefect was formed on the crack front. When the microdefect enlarged to a critical size, secondary microcracks nucleated at the stress-concentrated microdefect shoulders. Then, the microcracks propagated to two sides of the MPD through anodic dissolution, microcleavage or mciroshear, resulting in the formation of the river-like fractography and the discontinuous surface SCC cracks with or without surface slipping.