Environmentally Assisted Cracking: Theory and Practice: Stress Corrosion Cracking I
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Monday 8:30 AM
March 20, 2023
Room: Sapphire 410B
Location: Hilton
Session Chair: Gary Was, University of Michigan; John Scully, University of Virginia
8:30 AM Invited
Mechanistic Understanding of Irradiation Assisted Stress Corrosion Cracking: Gary Was1; 1University of Michigan
Irradiated austenitic alloys are susceptible to degradation in high temperature water by irradiation assisted stress corrosion cracking (IASCC). While a general understanding of the process is emerging, there are several interesting observations that may now be incorporated into a complete description of the mechanism. It is now known that the local stress at the grain boundaries at sites of dislocation channel impingement plays a critical role. The composition of the surface oxide over the grain boundary is believed to be a key factor, as are oxides that form down the grain boundary. Most recently, grain boundary migration has been observed in irradiated stainless steels. Other factors such as the presence of second phases near grain boundaries and the overall composition of the steel can significantly affect the cracking susceptibility. This paper will provide a mechanistic understanding of the IASCC process to date, incorporating the most recent observations and experimental results.
9:00 AM
Cold Spray Deposition for Mitigation and Repair of Stress Corrosion Cracking in Used Nuclear Fuel Storage Stainless Steel Canisters: Hwasung Yeom1; Nicholas Pocquette1; Jonathan Tatman2; Frank Pfefferkorn1; Kumar Sridharan1; 1University of Wisconsin Madison; 2Electric Power Research Institute
Sustainability of the current light water reactor (LWR) fleet depends on long-term safe storage of used nuclear fuel (UNF). Presently, UNF is stored in stainless steel canisters in a dry cask storage system (DCSS). Since permanent geological repositories have not been identified, the UNF storage time in DCSS is expected to be multiple decades. A concern in the extended storage of UNF in DSCC is susceptibility to chloride-induced stress corrosion cracking (CISCC) in the welded regions of the canisters. This study investigates cold spray coatings of 304L and 316L stainless steel and nickel on substrates of both sensitized 304L and 316L stainless steels which are the most common canister materials. Select results of this study, including microstructural characterization and stress measurements of the coatings, and performance in boiling MgCl2 tests and electrochemical corrosion tests in NaCl solution, and evaluation of the crack repair capabilities will be presented.
9:20 AM
Peening Technologies to Mitigate Initiation and Resurgence of Stress Corrosion Cracking in Dry Cask Storage Stainless Steel Canisters: John Lacy1; Hwasung Yeom1; Kumar Sridharan1; Stan Bovid2; Andrew Tieu3; Jon Tatman4; Willie3; Kenneth Ross5; 1University of Wisconsin-Madison; 2LSP Technologies ; 3VLN Technologies; 4Electric Power and Research Institute; 5Pacific Northwest nation Laboratory
Long-term storage of used nuclear fuel (UNF) is one of the key issues for sustainability of the current Light Water Reactor (LWR) fleet. The stainless-steel canisters used for storage in dry cask storage systems (DCSS) have a propensity for chloride-induced stress corrosion cracking (CISCC) due to combination of tensile stress at welds, susceptible microstructure, and corrosive chloride salt environment. This research is aimed at evaluating a variety of peening technologies, including, shot peening, laser shock peening, and pulsed water jet peening to mitigate initiation and growth of CISCC in DCSS canisters. Microstructural developments in the peened region including grain refinement and reorientation, deformation-induced martensite formation, and dislocation entanglements were examined. Compressive residual stress measurements and corrosion testing have been conducted to evaluate the effect peening has on pitting corrosion behavior and stress corrosion cracking.
9:40 AM
Coupled Analysis of Stress and Deformation Behavior in Transgranular Stress Corrosion Crack Tip Plasticity in Austenitic Stainless Steel: Haozheng Qu1; Rebecca Schaller2; Eric Schindelholz3; Janelle Wharry1; 1Purdue University; 2Sandia National Laboratories; 3Ohio State University
The objective of this study is to understand crack tip plasticity around transgranular chloride-induced stress corrosion cracks (TGCISCC) in austenitic stainless steel. TGCISCC is a critical degradation pathway for steels, but the micromechanisms of its propagation are not well understood. Here, 304L coupons loaded in four-point bending fixtures are immersed in boiling MgCl2 at 155°C to initiate CISCC. Strain distributions and microstructure around the crack tips are analyzed using high-resolution electron backscatter diffraction (HR-EBSD) and transmission electron microscopy (TEM). Stacking faults and dislocations are observed along the crack path and in grains ahead of crack tips. Shear stress concentrates in cracked grains, whereas tensile stress concentrates in uncracked surrounding grains. The different deformation behaviors in cracked grains and ahead of crack tip will be discussed in connection with the strain and stress analysis.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-8992 A.
10:00 AM Break
10:20 AM Invited
Hydrogen Interactions and Transport in Additively Manufactured Structural Alloys: Implications for Stress Corrosion Cracking and Hydrogen Embrittlement: John Scully1; James Burns1; Lauren Singer1; Zachary Harris1; 1University of Virginia
As hydrogen plays a pivotal role in environmentally assisted cracking susceptibility, comprehension and characterization of hydrogen-metal interactions in structural alloys is vital in the safe application of these materials in corrosive environments. Hydrogen uptake, diffusion, trapping, and transport behaviors of additively manufactured (AM) metallic alloys such as AERMET 100, 316L stainless steel, and 17-4 PH stainless steel can differ greatly from those of their analogous traditionally manufactured incumbents. Hydrogen-metal interactions are characterized through a combination of electrochemical techniques, such as barnacle cell electrode and hydrogen permeation; as well as hot extraction methods, such as thermal desorption spectroscopy and LECO hydrogen testing. The identification of specific microstructural features functioning as hydrogen traps or fast paths for transport in AM alloys compared to traditionally manufactured alloys is challenging. Progress can provide insight into hydrogen interactions that may affect mechanical properties. The ramifications towards hydrogen embrittlement and stress corrosion cracking are discussed.
10:50 AM
Improving Stress Corrosion Cracking of Type 304 Stainless Steel through Grain Boundary Engineering: Osama Alyousif1; 1Kuwait University
Grain Boundary Engineering (GBE) of Type 304 stainless steel have shown improvement on stress corrosion cracking behavior in boiling saturated magnesium chloride solutions. The microstructure development by applying thermo-mechanical processes revealed increased population of intergranular resistant twin related boundaries. The grain boundaries character distribution and grain boundaries network connectivity were analyzed to elucidate the materials behavior in the corrosive environment. Evidence of intergranular corrosion resistance by fractographic examination showed the role of twin related clusters in improving the time to failure as well as the rate of elongation for the materials tested.GBE can be an effective process to enhance the performance of stainless steels in corrosive environments however, the thermo-mechanical processes needed for GBE have to be well designed to obtain optimal microstructure.
11:10 AM
A Mechanistic Study on Dealloyed-induced Stress Corrosion Cracking Initiation of Alloy 800: Hooman Gholamzadeh1; Adil Shaik1; Kevin Daub1; Matt Topping1; Mark Daymond1; Suraj Persaud1; 1Queen's University
Despite their good resistance to general and localized corrosion, Fe- and Ni-based alloys can suffer from environmentally assisted cracking. Alloy 800 (Fe-32Ni-21Cr), for instance, has shown excellent in-service performance as the tubing material of CANDU steam generators for decades. However, this material can suffer from selective dissolution (dealloying) and stress corrosion cracking (SCC) in boiling caustic environments, where Fe and Cr are soluble. Dealloying results in formation of a brittle, nanoporous film enriched in the more noble element. This film may be a precursor to SCC via a cleavage mechanism. The mechanism of dealloying-induced SCC initiation in Alloy 800 is investigated at the nanoscale in boiling caustic solutions. Several state-of-the-art electron microscopy techniques are used to characterize the nanoscale chemistry and plastic deformation associated with crack initiation from a dealloyed layer. Results suggest that, upon fracture, a dealloyed layer may inject a high-energy micro-crack into the substrate material, initiating SCC.