Influences of gaseous environment on low growth-rate fatigue crack propagation in steels. Annual report No. 1, January 1980. Report No. FPL/R/80/1030
The influence of gaseous environment is examined on fatigue crack propagation behavior in steels. Specifically, a fully martensitic 300-M ultrahigh strength steel and a fully bainitic 2-1/4Cr-1Mo lower strength steel are investigated in environments of ambient temperature moist air and low pressure dehumidified hydrogen and argon gases over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, with particular emphasis given to behavior near the crack propagation threshold ..delta..K/sub 0/. It is found that two distinct growth rate regimes exist where hydrogen can markedly accelerate crack propagation rates compared to air, (1) at near-threshold levels below (5 x 10/sup -6/ mm/cycle) and (2) at higher growth rates, typically around 10/sup -5/ mm/cycle above a critical maximum stress intensity K/sub max//sup T/. Hydrogen-assisted crack propagation at higher growth rates is attributed to a hydrogen embrittlement mechanism, with K/sub max//sup T/ nominally equal to K/sub Iscc/ (the sustained load stress corrosion threshold) in high strength steels, and far below K/sub Iscc/ in the strain-rate sensitive lower strength steels. Hydrogen-assisted crack propagation at near-threshold levels is attributed to a new mechanism involving fretting-oxide-induced crack closure generated in moist (or oxygenated) environments. The absence of hydrogen embrittlement mechanisms at near-threshold levels is supported by tests showing that ..delta..K/sub 0/ values in dry gaseous argon are similar to ..delta..K/sub 0/ values in hydrogen. The potential ramifications of these results are examined in detail.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge (USA). Dept. of Mechanical Engineering
- DOE Contract Number:
- AC02-79ER10389
- OSTI ID:
- 5157733
- Report Number(s):
- DOE/ER/10389-1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHROMIUM-MOLYBDENUM STEELS
CRACKS
HYDROGEN
METALLURGICAL EFFECTS
AIR
ARGON
CONTROLLED ATMOSPHERES
FATIGUE
HYDROGEN EMBRITTLEMENT
MOBILITY
ALLOYS
ATMOSPHERES
CHROMIUM ALLOYS
CHROMIUM STEELS
CRYOGENIC FLUIDS
ELEMENTS
EMBRITTLEMENT
FLUIDS
GASES
IRON ALLOYS
IRON BASE ALLOYS
MECHANICAL PROPERTIES
NONMETALS
RARE GASES
STEELS
360103* - Metals & Alloys- Mechanical Properties