Hydrogen embrittlement, grain boundary segregation, and stress corrosion cracking of alloy X-750 in low- and high-temperature water
- Bettis Atomic Power Lab., West Mifflin, PA (United States)
The nature of intergranular stress corrosion cracking (SCC) of alloy X-750 was characterized in low- and high-temperature water by testing as-notched and precracked fracture mechanics specimens. Materials given the AH, BH, and HTH heat treatments were studied. While all heat treatments were susceptible to rapid low-temperature crack propagation (LTCP) below 150 C, conditions AH and BH were particularly susceptible. Low-temperature tests under various loading conditions (e.g., constant displacement, constant load, and increasing load) revealed that the maximum stress intensity factors (K{sub P{sub max}}) from conventional rising load tests provide conservative estimates of the critical loading conditions in highly susceptible heats, regardless of the load path history. For resistant heats, K{sub P{sub max}} provides a reasonable, but not necessarily conservative, estimate of the critical stress intensity factor for LTCP. Testing of as-notched specimens showed that LTCP will not initiate at a smooth surface or notch, but will readily occur if a cracklike defect is present. Comparison of the cracking response in water with that for hydrogen-precharged specimens tested in air demonstrated that LTCP is associated with hydrogen embrittlement of grain boundaries. The stress corrosion crack initiation and growth does occur in high-temperature water (>250 C), but crack growth rates are orders of magnitude lower than LTCP rates. The SCC resistance of HTH heats is far superior to that of AH heats as crack initiation times are two to three orders of magnitude greater and growth rates are one to two orders of magnitude lower.
- Research Organization:
- Bettis Atomic Power Lab. (BAPL), West Mifflin, PA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC11-93PN38195
- OSTI ID:
- 677970
- Report Number(s):
- WAPD-T-3149; TRN: IM9939%%26
- Resource Relation:
- Other Information: PBD: Jun 1999
- Country of Publication:
- United States
- Language:
- English
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