Mechanical property degradation and microstructural evolution of cast austenitic stainless steels under short-term thermal aging

Journal Article · Mon Jul 31 00:00:00 EDT 2017 · Journal of Nuclear Materials

DOI:https://doi.org/10.1016/j.jnucmat.2017.07.059· OSTI ID:1390578

Lach, Timothy G. ^[1]; Byun, Thak Sang ^[1]; Leonard, Keith J. ^[2]

---

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Nuclear Sciences Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division

We performed mechanical testing and microstructural characterization 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 h 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 δ-ferrite into α/α', precipitation of G-phase in the δ-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. Finally, the low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-76RL01830; DEAC05-76RL01830
• OSTI ID: 1390578
• Alternate ID(s): OSTI ID: 1549663
• Report Number(s): PNNL-SA-126351; PII: S0022311517307420
• Journal Information: Journal of Nuclear Materials, Vol. 497; ISSN 0022-3115
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
thermal aging degradation
embrittlement
duplex stainless steel
spinodal decomposition
solute segregation
G-phase precipitation