Effect of thermal aging on the corrosion fatigue crack growth of Z3CN20-09M stainless steels in simulated PWR primary water

Corrosion fatigue crack growth (CFCG) of thermally aged Z3CN20-09M cast austenitic stainless steel (CASS) was studied in simulated PWR primary water. Specimens were aged at 400 °C (6000 h, 16 000 h) and 450 °C (6000 h) and tested under varied loading conditions. The PWR primary water increased crack growth rates by typically up to 15 times compared to air, due to synergy between cyclic loading, corrosion, and the duplex microstructure, yet with weaker frequency and stress intensity dependence than conventional austenitic steels. Thermal aging had limited influence (acceleration factor < 4), indicating that ferrite decomposition does not substantially affect the crack-tip oxide film (inner spinel/outer magnetite bilayer) or its rupture behavior. The study further establishes that all measured corrosion fatigue crack growth rates consistently fall below the ASME Code Case N-809 design curve, validating its continued applicability as a conservative safety benchmark for aged CASS components in PWR envi-ronments.