08425 Effect of Shot Peening on the Oxidation of Ferritic-Martensitic Steels in Supercritical Water

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Product Number: 51300-08425-SG

ISBN: 08425 2008 CP

Author: Xiaowei Ren, Kumar Sridharan, and Todd Allen

Publication Date: 2008

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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.