Influence of Thermal Aging on the Mechanical and Corrosion Properties of C-22 Alloy Welds
The phase stability of C-22 alloy (UNS No. N06022) gas tungsten arc welds was studied by aging samples at 427, 482, 538, 593, 649, 704, and 760 C for times up to 40,000 hours. The tensile properties and the Charpy impact toughness of these samples were measured in the as-welded condition as well as after aging. The corrosion resistance was measured using standard immersion tests in acidic ferric sulfate (ASTM G 28 A) and 2.5% hydrochloric acid solutions at the boiling point. The microstructures of weld samples were examined using scanning electron microscopy (SEM). One weld sample (aged 40,000 hours at 427 C) was examined using transmission electron microscopy (TEM). The structure of the unaged welds was dendritic with tetrahedrally close-packed (TCP) phase particles in the interdendritic regions. Long-range order was seen in the weld aged at 427 C for 40,000 hours and was assumed to also occur in other welds aged below approximately 600 C. At temperatures above about 600 C, TCP phase nucleation and growth of existing particles occurred. This precipitation occurred near the original particles presumably in regions of the highest molybdenum (Mo) segregation. Lower temperatures had little or no effect on the morphology of TCP phases. The C-22 weld samples were approximately 25% stronger but 30-40% less ductile than the base metal. Strengthening of the weld during aging occurred significantly only at 593 C for the aging times investigated. Because strengthening was not seen at higher temperatures, it was assumed to be due to ordering which has been seen in C-22 base metal at this temperature. A small amount of strengthening was seen at 427 C after 40,000 hours where ordering was just beginning. The Charpy impact toughness was reduced dramatically with aging. The time at which this reduction occurred decreased as aging temperature increased suggesting that the reduced ductility is due to the presence and growth of the brittle TCP phases. The corrosion rate of weld samples tested in the standard ASTM G 28 A solution and in a 2.5% HCl solution was higher than was seen with C-22 base metal. After aging, however, the corrosion rate of weld and base metal samples became comparable.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 791304
- Report Number(s):
- UCRL-JC-137727; TRN: US200511%%20
- Resource Relation:
- Conference: Minerals-Metals-Materials Society Conference, St. Louis, MO (US), 10/08/2000--10/12/2000; Other Information: PBD: 15 Jun 2000
- Country of Publication:
- United States
- Language:
- English
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Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours
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Related Subjects
25 ENERGY STORAGE
AGING
ALLOYS
BOILING POINTS
CORROSION
CORROSION RESISTANCE
DUCTILITY
HYDROCHLORIC ACID
MOLYBDENUM
MORPHOLOGY
NUCLEATION
PHASE STABILITY
SCANNING ELECTRON MICROSCOPY
SEGREGATION
SULFATES
TENSILE PROPERTIES
TRANSMISSION ELECTRON MICROSCOPY
TUNGSTEN
Geothermal Legacy