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

Timothy G. Lach; Thak Sang Byun; Keith J. Leonard

doi:10.1016/j.jnucmat.2017.07.059

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

Timothy G. Lach, Thak Sang Byun, Keith J. Leonard

Research output: Contribution to journal › Article › peer-review

33 Scopus citations

Abstract

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 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. The low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.

Original language	English
Pages (from-to)	139-153
Number of pages	15
Journal	Journal of Nuclear Materials
Volume	497
DOIs	https://doi.org/10.1016/j.jnucmat.2017.07.059
State	Published - Dec 15 2017
Externally published	Yes

Funding

This research was sponsored by U.S. Department of Energy/Office of Nuclear Energy through Light Water Reactor Sustainability R&D Program. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract No. DEAC05-76RL01830 . APT and FIB/SEM were performed at PNNL's Environmental Molecular Sciences Laboratory, a Department of Energy - Office of Biological & Environmental Research national scientific user facility. The authors would like to thank Dr. Arun Devaraj of PNNL for help with APT and Dr. Matthew Olszta of PNNL for help with TEM/STEM.

Funders	Funder number
TEM/STEM
U.S. Department of Energy	DEAC05-76RL01830
Air Force Office of Scientific Research
Battelle
Biological and Environmental Research
Savannah River Operations Office, U.S. Department of Energy
Center for Environmental Sciences and Engineering

Keywords

Duplex stainless steel
Embrittlement
G-phase precipitation
Solute segregation
Spinodal decomposition
Thermal aging degradation

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

abstract = "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 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. The low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.",

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author = "Lach, {Timothy G.} and Byun, {Thak Sang} and Leonard, {Keith J.}",

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AU - Lach, Timothy G.

AU - Byun, Thak Sang

AU - Leonard, Keith J.

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Y1 - 2017/12/15

N2 - 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 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. The low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.

AB - 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 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. The low C, high Mo CF3M alloys experienced the most spinodal decomposition and G-phase precipitation coinciding the largest reduction in impact properties.

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KW - G-phase precipitation

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KW - Thermal aging degradation

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ER -

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

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