Effect of Thermal Ageing on the Corrosion Resistance of Stainless Steel Type 316L Exposed in Supercritical Water

Abstract

The tendency for intermetallic precipitates to form in austenitic stainless steel during prolonged exposure at the expected operating temperature of the fuel cladding in the Canadian supercritical water reactor (SCWR) concept represents a possible serious threat to the intrinsic in-service corrosion performance of the candidate alloy. The objective of this study was to better understand the extent to which a thermally-aged microstructure affects the mode and extent of corrosion exhibited by Type 316L stainless steel exposed in 25 MPa supercritical water (SCW) at 550 °C for 500 h. Mechanically-abraded samples were exposed in an as-received and thermally-aged condition. Thermal ageing conducted at 815 °C (peak fuel cladding temperature expected) for 1000 h was found to produce a discontinuous network of the carbide (M23C6), chi (χ), laves (η) and sigma (σ) phases. The similar weight gain and oxide scale structure, composition and thickness suggested that the thermally-aged condition does not have a marked influence on the corrosion resistance.