Hydrogen-Assisted Fracture of Stainless Steel

Technical Report · Fri Sep 20 00:00:00 EDT 2019

DOI:https://doi.org/10.2172/1562838· OSTI ID:1562838

Lawrence, Samantha Kay ^[1]; Balch, Dorian K. ^[1]; Yee, Grace ^[1]; Somerday, Brian P. ^[1]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Symmetric four-point bending (S4PB) and anti-symmetric four-point bending (AS4PB) were applied to assess the effect of hydrogen on crack initiation and propagation in a stable, nitrogen-strengthened austenitic stainless steel (21Cr-6Ni-9Mn). Specimens of a high strength aluminum alloy (AA2219-T851), which has also been identified as hydrogen-compatible, were used for test method development prior to completing the stainless steel test matrix. Single edge notched bend (SEN(B)) specimens were extracted from forged 21Cr-6Ni-9Mn bar and AA2219 plate. The 21Cr-6Ni-9Mn specimens were then hydrogen charged with ~200 wt. ppm hydrogen; AA2219 specimens were not charged. Aluminum specimens were tested in S4PB to induced mode I (pure bending), and AS4PB to attain varying levels of mode I/II mixity and mode II (pure shear), where the ratio of mode I to mode II varies with the position of the crack plane relative to the load line. After test method troubleshooting and validation, hydrogen charged stainless steel specimens were then subjected to mode I and two ratios of mixed mode I/II. Mode II loading was not achieved due to high load limitations. Analyses of fracture profiles for both materials reveal a marked effect of loading mode mixity on initial crack propagation orientation, however a specific contribution of hydrogen was not readily identifiable. Fracture initiation toughness in the presence of hydrogen, J_IH, was calculated following the J-integral approach; the mode I J_IH calculated for stainless steel samples fractured in S4PB were consistent with published values determined from compact tension specimens. The peak loads required to initiate fracture during AS4PB far exceeded those required during S4PB. This is attributed to the increasing shear force applied to the specimens as the degree of mode mixity increases. Ultimately, understanding the fracture response of hydrogen exposed stainless steels subjected to mixed mode I/II loading is critical for designing hydrogen containment vessels or gas transfer systems (GTS).

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1562838
• Report Number(s): SAND-2016-9981R; 648037
• Country of Publication: United States
• Language: English