Non-Linear Dynamics of the Morphology at the Oxide / Metal Interface of Austenitic Steels in Simulated Light Water Reactor Environments and its Implications for SCC Initiation

Takeda, Yoichi; Sato, Takayuki; Yamauchi, Daisuke; Shoji, Tetsuo; Ohji, Akio

doi:10.1007/978-3-319-48760-1_24

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“…The results of oxide film thickness were plotted in relation to weight gain/loss data of 316L and 316LN SS in Figure 13, which demonstrates particularly that the 316LN oxide film thickness increased while weight decreased. This implies that significant loss of alloying elements took place on 316LN under irradiation condition, which was discussed from an oxidation localization point of view in the reference [50]. Based upon the results outlined above, the observed behavior could be due to hydrogen formed by the transmutation of nitrogen in irradiated steels originating from the following transmutation [51]:…”

Section: Sem Observation-surface and Cross-sectionmentioning

confidence: 99%

Role of Hydrogen in Metal Oxidation—Implication to Irradiation Enhanced Corrosion of Ni-Based Alloys and Stainless Steels in High Temperature Water

Wang

Tanaka

2022

CMD

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Hydrogen plays various roles in metals or at metal–environment interfaces. Well known effects on metals are hydrogen embrittlement, hydrogen enhanced local plasticity, hydrogen enhanced strain-induced vacancy, hydrogen accelerated oxidation, hydrogen-induced creep, and their synergy. In this study, the potential roles of hydrogen in materials degradation are demonstrated and studied by two different tests. One is the high temperature oxidation of Ni-based alloy in various environments with hydrogen penetration, and the other is the effects of neutron flux/fluence on the oxidation kinetics and SCC of 316L and 316LN stainless steels, regarding a possible role of transmuted H from N. The results emphasize that the hydrogen either permeated into metals from surrounding environments, such as high temperature water or gaseous hydrogen, or generated in metals by nuclei transmutation, such as hydrogen transmuted from N atoms in metals, which can promote metal oxidation through multiple mechanisms. Apparently, the oxidation/corrosion phenomenon is a synergy of sub-mechanisms. For instance, dissolved hydrogen (DH) is usually believed to slow down the corrosion process for lowering the open circuit potential (OCP). However, H also facilitates the transport of the cations in oxide, thereby accelerating the corrosion process. In this bi-mechanism system, two different, contradictory mechanisms work and exist simultaneously. Therefore, whether the metallic materials are benefited or degraded by the H during its oxidation process depends on which sub-mechanism is dominant. Namely, hydrogen can play the role an oxidant in the metal and metal/oxide interface to pre-oxidize metal elements, such as Cr, Ni, and Fe, and possibly promote inward oxygen diffusion and the oxidation rate at the interface. Moreover, hydrogen may play a role as a reductant in oxides where existing oxides can be reduced. Then, the protective capability of oxides will be decreased to result in corrosion acceleration at the metal–oxide interface. These phenomena were observed in Ni-based alloy and possibly austenitic stainless steel containing N such as 316LN SS. This work demonstrates a part of the role of hydrogen on oxidation, and more extensive and systematic work is needed to delineate the role of hydrogen on oxidation with and without irradiation.

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Section: Sem Observation-surface and Cross-sectionmentioning

confidence: 99%