The mechanistic aspects of chloride-induced stress corrosion cracking and internal pitting in stainless steel

<title>Abstract</title> <p>The objective of this study is to understand the mechanistic drivers of chloride-induced stress corrosion cracking (CISCC). CISCC is a critical degradation mode in structural alloys exposed to chloride-rich environments, so understanding its deformation mechanisms is essential for the design and safe operation of these alloys. Although numerous studies have examined CISCC behavior, most have focused on electrochemical processes, leaving the mechanics of CISCC poorly understood. In this study, the deformation mechanisms of CISCC in austenitic stainless steel are investigated using high-angle-resolution electron backscatter diffraction (HR-EBSD) and controlled electron channeling contrast imaging (cECCI). The deformation fields along crack paths, near crack tips, and around internal pits are investigated in terms of residual elastic fields, GND density, and dislocation imaging. Results show that CISCC is highly sensitive to grain-scale plasticity, i.e., the availability of slip systems in a given grain. CISC cracks propagate through high-Schmid-factor grains via extensive plasticity, while they propagate through lower-Schmid-factor grains in close alignment with the {111} planes with minimal plasticity. Characteristic peanut-shaped plastic zones, along with mixed-mode cracking, are observed, analogous to mechanically driven cracks. In addition, the formation of internal pits, a newly emergent phenomenon in CISCC, is determined to be caused by stepwise crack propagation during brittle fracture promoted by localized accelerated corrosion at the crack tip. Using state-of-the-art characterization of deformation fields, this study develops the mechanistic underpinnings of CISC crack propagation and internal pitting, which can be used to engineer grain-orientation-based CISCC resilience in structural alloys.</p>