Creep-rupture behavior of iron superalloys in high-pressure hydrogen
The creep-rupture behavior of a newly developed cast alloy NASAUT 4G-A1 with 15% Cr, 15% Mn, and 1.5% C was evaluated in 15 MPa H/sub 2/ at 775/sup 0/C and 825/sup 0/C; the alloy is intended for automotive Stirling heater head application. Rupture life, minimum creep rate, and time to 1% strain data were analyzed. The 3500-h mean rupture stress at 775/sup 0/C is 140 MPa, exceeding the design stress of 119 MPa. However, significant data scatter caused the 90% confidence level lower limit of the mean stress to be 94.3 MPa, falling below the 119 MPa design stress level. NASAUT 4G-A1 3500-h rupture-life mean stress exceeds the XF-818 values but is lower than SA-F11, HS-31, and CRM-6D (aged). The predicted mean stress to 1% creep in 3500 h was 57.8 MPa and had a very wide scatter indicating a lack of reproducibility in the alloy structure. For a cast alloy, NASAUT 4G-A1 indicated significant ductility with maximum elongation in the range of 6.0 to 13.6% at 775/sup 0/C. Hydrogen did not seem to affect the stable carbides though some methane was noted in the chamber gas. The microstructure contained some voids, pores, inclusions, and interdendritic separations. The structure consisted of an austenitic phase with two different carbides and was not affected by heat treatment.
- Research Organization:
- IIT Research Inst., Chicago, IL (USA)
- DOE Contract Number:
- AI01-77CS51040
- OSTI ID:
- 6324730
- Report Number(s):
- DOE/NASA-0363-1; NASA-CR-175027; ON: DE86005013
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CHROMIUM ALLOYS
CREEP
CRYSTAL STRUCTURE
ELEMENTS
ENGINES
FAILURES
FRACTOGRAPHY
HEAT ENGINES
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
HEAT TREATMENTS
HYDROGEN
IRON ALLOYS
IRON BASE ALLOYS
MANGANESE ALLOYS
MATERIALS
MATERIALS TESTING
MECHANICAL PROPERTIES
MICROSTRUCTURE
NONMETALS
RUPTURES
STIRLING ENGINES
TESTING