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TEM investigation of intergranular stress corrosion cracking for 316 stainless steel in PWR environment

Department of Materials, University of Oxford, Oxford, England, United Kingdom
Acta Materialia (Impact Factor: 4.47). 02/2006; 54(3):635-641. DOI: 10.1016/j.actamat.2005.10.011

ABSTRACT Type 316 stainless steel foils containing stress corrosion cracks grown in high temperature aqueous environments have been examined by transmission electron microscopy. It was found that the crack tips are oxidized and have a three-layered morphology where all the layers taper towards the crack tip. The inner layer is a microcrystalline spinel sandwiched between the outer layers of a nano-crystalline oxide. The outer layers are enriched in Cr, and the inner with Fe, relative to the matrix. Cu was observed to segregate at the interface between oxide and matrix at one crack in type 316 steel. The inner oxide growth is dominated by different mechanisms before and after the grain boundary cracks.

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    • "Type 316L stainless steel (SS) is a corrosion resistant alloy because of its tendency to form a protective oxide film, for which a great of data exists [1] [2] [3]. However, certain corrosion degradations, such as stress corrosion cracking (SCC) [4] [5] [6] [7] [8], have been observed on this material when it was used in nuclear power systems. The oxide films formed on stainless steels in the primary circle of steam generators and nuclear reactors are supposed to play a significant role in the process of SCC [9] [10] [11]. "
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    Corrosion Science 11/2010; 52(11):3646–3653. DOI:10.1016/j.corsci.2010.07.013 · 3.69 Impact Factor
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    • "(a) are 0.3063nm (d220) and 0.4847nm (d111), which correspond to spinel [13]. "
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    ABSTRACT: The electrochemical behavior of a low alloy steel (Fe-2.25 Cr-1Mo) was investigated in 1 m NaCl over a range of temperatures (75-2500C) with various levels of contaminations with CuCl2. The change in free corrosion potential with time and the anodic and cathodic potentiodynamic polarization were measured. Cyclic potentiodynamic polarization was also measured on a previously corroded electrodes for different times (7 and 72 hrs) either in the same or in a fresh electrolyte. The results revealed that the corrosion potential is shifted, at all temperatures, towards more noble values to an extent which increases with the concentration of CuCl2. The cathodic current density also increases as the concentration of CuCl2 increases. CuCl2 acts as cathodic depolarizer. It undergoes electrodeposition leading to the formation of Cu metal onto the corrosion product, which becomes less adherent and less protective. Most of this Cu metal falls off the alloy surface along with the spalled corrosion product. The shift in the corrosion potential towards more noble values with the increase in the precorrosion time, in absence of Cu2+ ions, indicates that the corrosion product which forms protect the surface against further attack. In the presence of Cu2+ ions, the passivation occurred after the effect of copper is diminished.
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