Dynamical In Situ Study of Morphological Variations on Stainless Steel in a Sour Corrosive Environment

It is still unclear how environmentally assisted cracking, especially sulfide stress cracking (SSC), is caused by corrosion and fracture behavior. In this study, a new in situ technique for an SSC visualization challenge was established and applied for the visualization of microcrack propagation resulting from a single pitting on the steel surface of 13% Cr martensitic stainless steel during four-point bending SSC tests and discussed by combining ex situ x-ray computed tomography (XCT) and electron backscatter diffraction (EBSD). The dynamic behavior of microcracks was visualized successfully, and the microbubbles behavior with the corrosion reaction was also captured. Regarding the relationship between internal structure and microstructure for cracking, it was found that a cavity was formed in the interior of prior to the cracks seen on the surface by XCT, and cracks by EBSD were propagated along prior austenite grain boundaries. On the basis of in situ observations and complementary ex situ analyses, the actual situation of crack on the steel surface was revealed and discussed with both corrosion and fracture over time. This approach provides an opportunity to clarify the SSC occurrence process based on actual SSC tests and contributes to the determination of phenomenological criteria. Furthermore, by combining this in situ technique with commonly known electrochemical measurements such as polarization curves, open-circuit potentials, and electrochemical impedance spectroscopy, it is possible to directly discuss various electrochemical data corresponding to corrosion and fracture behavior, including dissolution and gas evolution.