The environmental effect on corrosion fatigue behavior of austenitic stainless steels
Name
1088722872-MIT.pdf
Description
Full printable version
Size
7.99 MB
Format
Adobe PDF
Checksum (MD5)
0ebd47c9bf304ad5592d3ed8c2d5ba07
Author(s)
Yu, Lun, Ph. D. Massachusetts Institute of Technology
Advisor(s)
Ronald G. Ballinger.
Date Issued
2017
Publisher
Massachusetts Institute of Technology
Abstract
Corrosion fatigue is a multivariate challenge that threatens the lifetime of service of nuclear power plant materials, especially austenitic stainless steels. Both enhancement and retardation of crack growth have been observed in laboratory tests. This thesis work performs high temperature autoclave testing, post-test characterization and mechanistic modeling to understand the corrosion fatigue behavior of austenitic stainless steels in simulated light water reactor (LWR) environments. Crack growth rate (CGR) data were generated from the autoclave testing on low (0.001 wt.%) and high (0.03 wt.%) sulfur content heat 1T compact tension (CT) specimens. Tests were controlled under constant K (22-35 MPa [square root of]m) with load ratio of 0.7 and sawtooth waveform (85% rise vs. 15% fall), and at pH =10 and 288 °C with system pressure of 9.54 MPa. Crack enhancement was observed in low sulfur content heat specimens, and the CGR increases as the loading rise time increases. The fracture surfaces of low sulfur content heat specimens showed transgranular features with facets ("river pattern") and few oxide particles. Crack retardation was observed in high sulfur content heat specimens, and the CGR decreases as the loading rise time increases. The fracture surfaces of high sulfur content heat specimens showed distinct features at different rise time step. Transgranular features ("river pattern") were observed at short rise time step, while non-descript surfaces with fine octahedral oxide particles were observed at long rise time step. Additionally, tests in deuterium water were performed to enable measurements on hydrogen/deuterium concentrations in specimens using ToF-SIMS and hot vacuum extraction techniques. Deuterium pick-up from the testing environment was observed, and the enrichment of deuterium/hydrogen ahead of crack tip was also observed. Controlled experiments were also conducted, where specimens were baked prior to the autoclave testing to remove the residual internal hydrogen. Such heat treatment removing the internal hydrogen was found to not affect the crack growth behavior. Dissolved gases, hydrogen and argon respectively, were bubbled into system during the autoclave tests, and they resulted in similar crack growth behaviors. Modeling indicates that there exists an enhancement mechanism other than corrosion mass removal driving the crack growth in simulated LWR environments. Possibly it comes from the effect of corrosion-generated hydrogen. Retardation behavior and experimental observations could be understood and explained by concept and modeling of corrosion blunting. The results suggest excess conservatism of current ASME standards N-809 for high sulfur content austenitic stainless steels.
Description
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Subjects
Nuclear Science and Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
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