Mechanical testing and microstructural characterization were performed on short-term thermally aged cast austenitic stainless steels (CASS) to understand the severity and mechanisms of thermal-aging degradation experienced during extended operation of light water reactor (LWR) coolant systems. Four CASS materials – CF3, CF3M, CF8, and CF8M – were thermally aged for 1500 hours at 290 °C, 330 °C, 360 °C, and 400 °C. All four alloys experienced insignificant change in strength and ductility properties but a significant reduction in absorbed impact energy. The primary microstructural and compositional changes during thermal aging were spinodal decomposition of the d-ferrite into a/ a`, precipitation of G-phase in the d-ferrite, segregation of solute to the austenite/ ferrite interphase boundary, and growth of M23C6 carbides on the austenite/ferrite interphase boundary. These changes were shown to be highly dependent on chemical composition, particularly the concentration of C and Mo, and aging temperature. A comprehensive model is being developed to correlate the microstructural evolution with mechanical behavior and simulation for predictive evaluations of LWR coolant system components.
Revised: February 28, 2020 |
Published: November 13, 2017
Citation
Lach T.G., T. Byun, and K.J. Leonard. 2017.Mechanical Property Degradation and Microstructural Evolution of Cast Austenitic Stainless Steels under Short-term Thermal Aging.Journal of Nuclear Materials 497.PNNL-SA-126351.doi:10.1016/j.jnucmat.2017.07.059