Triple Ion-Beam Studies of Radiation Damage in 9Cr2WVTa Ferritic/Martensitic Steel for a High Power Spallation Neutron Source Page: 2 of 16
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Introduction
Austenitic and ferritic steels are potential candidate alloys for structural materials for the
Spallation Neutron Source (SNS). In an earlier paper [1], the results for accelerator-irradiated
316LN austenitic steel were reported. This paper summarizes the results for 9Cr-2WVTa
ferritic/martensitic steel. This reduced-activation steel was chosen for investigation because of
its excellent response to neutron irradiation compared with conventional Cr-Mo steels [2]. The
major weakness of ferritic steels is that irradiation affects toughness by causing a large increase
in ductile-brittle transition temperature (DBTT) and decrease in upper-shelf energy (USE) in a
Charpy impact test. The 9Cr-2WVTa alloy was developed as a reduced-activation steel in the
U.S. fusion program, in which Mo and Nb in conventional Cr-Mo steels were replaced with W
and Ta, respectively [3,4]. Substantial data have been generated for this alloy subjected to
fission neutron irradiation [2], but none for the SNS condition. However, information on
radiation damage effects in the SNS environment is urgently needed for design purposes. Under
the SNS environment, damage may be worse than in fission reactors due to the very high energy
protons (1 GeV), neutrons with energies from the proton energy down to thermal energies, and
high concentrations of transmutation products, particularly hydrogen and helium. In an effort to
obtain materials performance data in such a severe irradiation environment, experiments were
carried out using the Triple Ion Facility (TIF) at ORNL. The TIF was used because it can
simulate the gas/dpa ratios expected in the SNS environment.
Experimental
Transmission electron microscopy (TEM) specimen disks were prepared from Heat No.
3791 of the 9Cr-2WVTa ferritic/martensitic steel. Nominal alloy composition is Fe-9Cr-2W-
0.25V-0.12Ta-O.1C in weight percent [2]. Disk specimens were austenized 0.5 h at 1050 C
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Lee, EH. Triple Ion-Beam Studies of Radiation Damage in 9Cr2WVTa Ferritic/Martensitic Steel for a High Power Spallation Neutron Source, report, August 1, 2001; United States. (https://digital.library.unt.edu/ark:/67531/metadc739443/m1/2/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.