Microstructural Characterization of SCC Crack Tip and Oxide Film for SUS 316 Stainless Steel in Simulated PWR Primary Water at 320.DEG.C.

Abstract

Recent studies on stress corrosion cracking (SCC) behaviors of austenitic stainless steels in hydrogenated hightemperature water show that low potential SCC (LPSCC) can occur on cold-worked SUS 316 stainless steel (hereinafter, 316SS). In this study, oxide films and crack tips on cold-worked 316SS exposed to hydrogenated high-temperature water were characterized using analytical transmission electron microscopy (ATEM), grazing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES) in order to study the corrosion and SCC behaviors of these films and crack tips. A double layer structure was identified for the oxide film after a constant extension rate tensile (CERT) test. The outer layer was composed of large particles (0.2-3 mm) of Fe 3 O 4 and the inner layer consisted mainly of fine particles ($10 nm) of FeCr 2 O 4 . In addition, nickel enrichment was identified at the metal/oxide interface. Particles of Fe 3 O 4 were also identified on the crack walls. These results indicate that the same electrochemical reactions had occurred inside and outside the crack. The crack tip area was filled with corrosion products of a chromium-rich oxide. In addition, nickel enrichment was observed at the crack tip. The formation of the nickel-enriched phase indicates that a selective dissolution reaction of iron and chromium occurred at the front of the LPSCC crack.

Characterization Of Oxide Layers Produced On The AISI 321 Stainless Steel After Annealing

“…Chemical composition results obtained using SEM with EDX and XRD show that the oxide layer, from the surface side, was mainly composed of Cr 2 O 3 and Fe 3 O 4 . It is generally agreed that the oxide films are formed by diffusion of Fe to the outer oxide layer [14]. The analysis of EDS chemical composition revealed diversified stratification of oxides.…”

Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

“…The thickness of this layer, also named interfacial layer, varies from 20 to 30 nm. The duplex nature of the oxide layer morphology for an austenitic stainless steel exposed to reactor primary water has been reported by many authors [16][17][18][19][20].…”

“…12) are included in this 5 lm area of intergranular penetrations that may explain the depletion of chromium in the bulk highlighted in the last section, the amount of chromium available in the bulk being used in grain boundaries for intergranular precipitation. Moreover, 3D tomography of 16 O element (not shown here) shows that the oxygen is segregated in subsurface along the grain boundaries (shown in Fig. 13) and not along the localized deformation bands (width $100 nm).…”

“…-27 Al 16 O: Aluminum is thermodynamically reactive with oxygen in high temperature water and is preferentially oxidized; aluminum oxide is then systematically detected. The elemental intensity signal versus depth, from the base metal to the oxide layer for 16 O and 12 C and for the metal oxides ( 16 OTi, 16 OCr, 16 OAl, 16 OFe and 16 ONi) is reported in Fig. 12.…”

“…In order to confirm the presence of oxide penetration, the levels of different components ( 12 C, 16 O, 16 O 52 Cr, 16 O 56 Fe) were mapped at two depths: 5 lm and 15 lm where the oxygen signal intensity was disrupted and are displayed in Fig. 13 Mapping the levels of 12 C element at 5 and 15 lm depth showed that the signal was intensified at precise areas surrounded by dark.…”