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• Oxidation and SCC behaviour of 309 L/308 L SS welds were studied in PWR primary water. • There was no indication of SCC for low alloy steel (LAS) after SSRT tests. • The oxidation resistance of 309 L SS was lower than that of 308 L SS. • 309 L SS was more susceptible to SCC than 308 L SS in PWR primary water. Oxidation resistance and stress corrosion cracking (SCC) susceptibility of A508Ⅲ-309 L/308 L stainless steel (SS) claddings were investigated in simulated pressurized water reactor (PWR) primary water following a microstructure characterization. Preferential oxidation of slip bands was observed in 309 L SS. The oxidation resistance of 309 L SS was found to be lower than that of 308 L SS due to the higher Cr- and ferrite-content in 308 L SS than in 309 L SS after cladding. There was no indication of SCC for low alloy steel (LAS) after slow strain rate tensile (SSRT) tests. The presence of type-I and type-II boundaries, composition dilution and less δ-ferrite content synergistically contributed to increasing the SCC susceptibility of 309 L SS cladding. The effect of chemical composition and microstructure on SCC performance of the SS claddings was discussed. [ABSTRACT FROM AUTHOR]

The surfaces of 316L stainless steel with mechanical polishing (MP) or electropolishing (EP) in the presence of a magnetic field (MEP) before and after exposure to simulated pressurized water reactor (PWR) primary water were characterized by various techniques such as SEM, Raman spectroscopy, XPS and TEM measurements. The surface microhardness was lower and the surface roughness was higher for the as-treated MEP specimen than for the as-treated MP specimen. The oxide films that formed on the as-treated MP and MEP surfaces were nanometer-thick and rich in chromium. The Cr/(Fe + Ni) ratio of the as-treated MEP surface film was higher than that of the as-treated MP surface film. After exposure to simulated PWR primary water at 310 °C for 1050 h, a dark double oxide layer that was approximately 662 nm thick formed on the MP surface, while the MEP surface retained its original brightness as before exposure with a nanometer-thick oxide layer with a high Cr content. The MP and MEP specimens showed different oxidation kinetics when exposed to high temperature water. The high Cr/(Fe + Ni) ratio of the surface film on the MEP 316L SS contributed to its excellent oxidation resistance in simulated PWR primary water. • 316L SS treated by magneto-electropolishing (MEP) under a magnetic field. • About 2 nm thick oxide film on as-treated mechanically polished (MP) and MEP surfaces. • A double layer sub-micrometer thick oxide on exposed MP surface in PWR water. • A nanometer-thick oxide of high Cr content on exposed MEP surface in PWR water. • High Cr/(Fe + Ni) ratio of MEP surface contributed to its excellent oxidation resistance. [ABSTRACT FROM AUTHOR]

The effect of prior single tensile overloading on the stress corrosion cracking behavior of cold rolled 316L in a simulated PWR water environment at 310 °C was investigated. SCC growth retardation by overloading was observed in cold rolled 316L specimens in both the T-L and L-T orientations. The stretch zone observed on the fracture surfaces of the overloaded specimens affected SCC propagation. The compressive residual stress induced by overloading process reduced the effective driving force of SCC propagation. The negative dK/da effect ahead of the crack tip likely contributes to the retardation of SCC growth. The duration of overloading is dependent on water chemistry and the local stress conditions. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) growth behaviors of 309L and 308L stainless steel claddings in simulated pressurized water reactor primary water at 325 °C and 350 °C were investigated by compact tension specimens and correlated to the oxide film properties in terms of microstructure. SCC growth rates of 308L were much lower than those of 309L. 309L showed typical intergranular SCC characteristics. The high SCC resistance of 308L was related to the low oxidation rate and crack tip retardation due to the presence of highly networked ferrites. The lower Cr content, as well as less and sparsely distributed δ-ferrite phases in 309L than in 308L, led to more severe local oxidation penetration beneath the metal/inner oxide interface and more porous inner oxide, therefore, contributed to its enhanced SCC growth in 309L. The SCC growth rate results by compact tension specimens are consistent with those by slow strain rate tests. [ABSTRACT FROM AUTHOR]