The effect of shot peening on the oxidation behavior of NF616, a ferritic-martensitic (F/M) steel in supercritical water (SCW) has been investigated because of the potential applications of NF616 in future Generation IV nuclear reactor systems. Shot peening significantly reduces the grain size in the near-surface regions of this steel, thereby altering the diffusion characteristics of elements in the modified surface layer during high temperature exposure. This refined grain structure can alter surface-induced corrosion mechanisms of NF616 without changing its bulk properties. After exposure to SCW with a test section inlet dissolved oxygen content of 25 ppb at 500°C for up to 667 hours, both as-received (AR) and shot-peened (SP) samples formed a duplex oxide layer, including an iron-rich outer magnetite oxide layer and an inner layer consisting of chromium-containing spinel oxide and ferrite. A larger iron/oxygen ratio was observed in the outer oxide layer of the shot-peened samples, indicating enhanced diffusion of iron during the growth of the oxide layer. Chromium diffusion was also notably enhanced for shot-peened samples due to the finer grain size in the near-surface region.

Subject
Grain size, Materials, Oxides, Microstructure, Diffusion, Chromium, Oxide layers, Steel, Magnetite, Grain boundary, Shot peening, Grain, Oxidation
Keywords:
shot-peening, microstructure, oxidation, supercritical water, NF616
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2008
GOV
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