Evolution of the role of molybdenum in duplex stainless steels during thermal aging: From enhancing spinodal decomposition to forming heterogeneous precipitates

Timothy G. Lach; David A. Collins; Thak Sang Byun

doi:10.1016/j.jnucmat.2021.153268

Evolution of the role of molybdenum in duplex stainless steels during thermal aging: From enhancing spinodal decomposition to forming heterogeneous precipitates

Timothy G. Lach, David A. Collins, Thak Sang Byun

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

15 Scopus citations

Abstract

Thermal aging of ferrite in duplex stainless steels leads to a complex microstructural evolution that can give way to large deleterious changes in mechanical properties. The microstructural evolution mechanisms that happen concurrently are strongly linked to minor changes in composition. By characterizing duplex stainless steels with various compositions over a range of aging conditions, it was revealed that adding a modest amount of Mo to cast austenitic stainless steel (such as changing from grade CF3 to grade CF3M) not only increases the kinetics of spinodal decomposition and Ni-Si-Mn-rich G-phase precipitation, but it also forms a separate Mo-rich phase. At shorter equivalent aging times, Mo segregates from Fe and towards Cr accelerating spinodal decomposition. At longer aging times, Mo enriches in the Ni-Si-Mn clusters before phase separating into an adjoined Mo-rich cluster. These phase changes and precipitation events result in a rather steep drop in fracture and impact toughness. These results will inform the design of similar alloys for use at high temperatures.

Original language	English
Article number	153268
Journal	Journal of Nuclear Materials
Volume	557
DOIs	https://doi.org/10.1016/j.jnucmat.2021.153268
State	Published - Dec 15 2021

Funding

This research was partly sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725 . The analysis was based upon the result of experiment research supported by the Light Water Reactor Sustainability Program for the U.S. Department of Energy, Office of Nuclear Energy (LW-18OR040215) at Pacific Northwest National Laboratory (PNNL) operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract No. DEAC05-76RL01830. The authors would like to thank Arun Devaraj, William Frazier, and Emily Barkley at PNNL for thoughtful discussion and aid in experiments. APT was performed at PNNL's Environmental Molecular Sciences Laboratory, a Department of Energy - Office of Biological & Environmental Research national scientific user facility. FIB/SEM was performed at PNNL's Radiological Microscopy Suite at the Radiochemical Processing Laboratory and PNNL's Institutional Microscopy Tools.

Keywords

Atom probe tomography (APT)
Duplex stainless steel
Fracture toughness
Precipitation
Spinodal decomposition
Thermal aging

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10.1016/j.jnucmat.2021.153268

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title = "Evolution of the role of molybdenum in duplex stainless steels during thermal aging: From enhancing spinodal decomposition to forming heterogeneous precipitates",

abstract = "Thermal aging of ferrite in duplex stainless steels leads to a complex microstructural evolution that can give way to large deleterious changes in mechanical properties. The microstructural evolution mechanisms that happen concurrently are strongly linked to minor changes in composition. By characterizing duplex stainless steels with various compositions over a range of aging conditions, it was revealed that adding a modest amount of Mo to cast austenitic stainless steel (such as changing from grade CF3 to grade CF3M) not only increases the kinetics of spinodal decomposition and Ni-Si-Mn-rich G-phase precipitation, but it also forms a separate Mo-rich phase. At shorter equivalent aging times, Mo segregates from Fe and towards Cr accelerating spinodal decomposition. At longer aging times, Mo enriches in the Ni-Si-Mn clusters before phase separating into an adjoined Mo-rich cluster. These phase changes and precipitation events result in a rather steep drop in fracture and impact toughness. These results will inform the design of similar alloys for use at high temperatures.",

keywords = "Atom probe tomography (APT), Duplex stainless steel, Fracture toughness, Precipitation, Spinodal decomposition, Thermal aging",

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AU - Collins, David A.

AU - Byun, Thak Sang

PY - 2021/12/15

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N2 - Thermal aging of ferrite in duplex stainless steels leads to a complex microstructural evolution that can give way to large deleterious changes in mechanical properties. The microstructural evolution mechanisms that happen concurrently are strongly linked to minor changes in composition. By characterizing duplex stainless steels with various compositions over a range of aging conditions, it was revealed that adding a modest amount of Mo to cast austenitic stainless steel (such as changing from grade CF3 to grade CF3M) not only increases the kinetics of spinodal decomposition and Ni-Si-Mn-rich G-phase precipitation, but it also forms a separate Mo-rich phase. At shorter equivalent aging times, Mo segregates from Fe and towards Cr accelerating spinodal decomposition. At longer aging times, Mo enriches in the Ni-Si-Mn clusters before phase separating into an adjoined Mo-rich cluster. These phase changes and precipitation events result in a rather steep drop in fracture and impact toughness. These results will inform the design of similar alloys for use at high temperatures.

AB - Thermal aging of ferrite in duplex stainless steels leads to a complex microstructural evolution that can give way to large deleterious changes in mechanical properties. The microstructural evolution mechanisms that happen concurrently are strongly linked to minor changes in composition. By characterizing duplex stainless steels with various compositions over a range of aging conditions, it was revealed that adding a modest amount of Mo to cast austenitic stainless steel (such as changing from grade CF3 to grade CF3M) not only increases the kinetics of spinodal decomposition and Ni-Si-Mn-rich G-phase precipitation, but it also forms a separate Mo-rich phase. At shorter equivalent aging times, Mo segregates from Fe and towards Cr accelerating spinodal decomposition. At longer aging times, Mo enriches in the Ni-Si-Mn clusters before phase separating into an adjoined Mo-rich cluster. These phase changes and precipitation events result in a rather steep drop in fracture and impact toughness. These results will inform the design of similar alloys for use at high temperatures.

KW - Atom probe tomography (APT)

KW - Duplex stainless steel

KW - Fracture toughness

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KW - Thermal aging

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Evolution of the role of molybdenum in duplex stainless steels during thermal aging: From enhancing spinodal decomposition to forming heterogeneous precipitates

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