Fracture Resistance of Cast Stainless Steels after Thermal Aging for up to 10000 Hours

Technical Report · Fri Sep 14 00:00:00 EDT 2018

DOI:https://doi.org/10.2172/3012294· OSTI ID:3012294

Byun, Thak Sang; Collins, David A.; Barkley, Emily L.; Lach, Timothy G.

This work package, Cast Stainless Steel Aging, aims to achieve a comprehensive scientific understanding on the aging and failure phenomena in cast austenitic stainless steels (CASSs) using holistic experimental and modeling means and to provide a practical and science-based model to predict the degree of thermal degradation of CASS components in extended-term operations. The test materials in the project include four model CASSs (CF3, CF3M, CF8, and CF8M), four EPRI-provided CASSs (CF3, two CF8s, and CF8M), and two reference wrought materials (304L and 316L), which contain a wide variety of d-ferrite contents (2–33%). These materials have been thermally aged at two light water reactor (LWR)-relevant temperatures (290 and 330°C) and at two accelerated-aging temperatures (360 and 400°C) for up to three years. In the fiscal year, the fracture toughness testing and J-R curve calculation were completed for the ten CASS and wrought materials aged up to 10,000 hours. This report is to present the results of the static fracture (J-R) testing for the model and EPRI-provided CASS materials after thermal aging up to 10,000 hours. First, a new aging parameter (A) was defined to present the aging degradation of mechanical properties against the common variable. This definition is used to scale an aging time at a temperature to the effective aging time at a reference temperature based on Arrhenius equation, which is a rate theory equation for thermally activated mechanisms. Second, the fracture test results are presented in the forms of fracture resistance (J-R or J-?a) curves, KJQ versus A curves, and tabulated crack length and fracture toughness data for ~460 fracture tests. Third, the fracture test results indicate that the fracture toughness tends to increase in early aging; after a short time, however, it decreases with aging parameter at a rate depending on the volume fraction of d-ferrite. Overall, the decrease of static fracture toughness due to thermal aging is less significant than that of Charpy impact energy, which usually is measured as the reduction of upper shelf energy and shift of ductile-brittle transition temperature. Finally, a preliminary conclusion is derived for the static fracture behavior of aged CASS materials; which states that the cast stainless steels with d-ferrite contents less than ~20% will not be subjected to a significant reduction of static fracture toughness or embrittlement over the extended lifetimes of reactors.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 3012294
• Report Number(s): PNNL-27923
• Country of Publication: United States
• Language: English