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Title: Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments

Abstract

The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River to provide required data for establishing safe operating conditions and lifetimes of pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless-steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharging with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to buildin decay helium prior to testing. ASTM J-Integral fracture mechanics analyses, transmission electron microscopy (TEM), and small angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product, helium-3. Results show that the fracture toughness values were reduced to less than 2-4% of the as-forged values for specimens with more than 1300 appm helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant tomore » tritium-induced cracking than Type 21-6-9 stainless at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.« less

Authors:
 [1];  [1]; ORCiD logo [1];  [1]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Publication Date:
Research Org.:
Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Sponsoring Org.:
USDOE Office of Environmental Management (EM)
OSTI Identifier:
1616263
Report Number(s):
SRNL-STI-2019-00249
Journal ID: ISSN 1536-1055
Grant/Contract Number:  
AC09-08SR22470
Resource Type:
Accepted Manuscript
Journal Name:
Fusion Science and Technology
Additional Journal Information:
Journal Volume: 76; Journal Issue: 3; Journal ID: ISSN 1536-1055
Publisher:
American Nuclear Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Morgan, Michael J., Hitchcock, Dale A., Krentz, Timothy M., and West, Scott L. Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments. United States: N. p., 2020. Web. https://doi.org/10.1080/15361055.2019.1704138.
Morgan, Michael J., Hitchcock, Dale A., Krentz, Timothy M., & West, Scott L. Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments. United States. https://doi.org/10.1080/15361055.2019.1704138
Morgan, Michael J., Hitchcock, Dale A., Krentz, Timothy M., and West, Scott L. Fri . "Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments". United States. https://doi.org/10.1080/15361055.2019.1704138. https://www.osti.gov/servlets/purl/1616263.
@article{osti_1616263,
title = {Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments},
author = {Morgan, Michael J. and Hitchcock, Dale A. and Krentz, Timothy M. and West, Scott L.},
abstractNote = {The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River to provide required data for establishing safe operating conditions and lifetimes of pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless-steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharging with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to buildin decay helium prior to testing. ASTM J-Integral fracture mechanics analyses, transmission electron microscopy (TEM), and small angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product, helium-3. Results show that the fracture toughness values were reduced to less than 2-4% of the as-forged values for specimens with more than 1300 appm helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant to tritium-induced cracking than Type 21-6-9 stainless at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.},
doi = {10.1080/15361055.2019.1704138},
journal = {Fusion Science and Technology},
number = 3,
volume = 76,
place = {United States},
year = {2020},
month = {4}
}

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Works referenced in this record:

Investigation of microstructural evolution under neutron irradiation in Eurofer97 steel by means of small-angle neutron scattering
journal, April 2009


Helium bubble evolution in F82H-mod – correlation between SANS and TEM
journal, August 2004


Tritium-Helium Effects in Metals
journal, September 1985


Tritium and Decay Helium Effects on Cracking Thresholds and Velocities in Stainless Steel
journal, March 2001


Fracture toughness of type 304 and 316 stainless steels and their welds
journal, January 1997


Gas densities in he bubbles and their size distribution in nickel measured by neutron scattering
journal, December 1983


Hydrogen induced ductility losses in austenitic stainless steel welds
journal, February 1981

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