Comparison of the effects of long-term thermal aging and HFIR irradiation on the microstructural evolution of 9Cr-1MoVNb steel
Both thermal aging at 482--704{degree}C for up to 25,000h and HFIR irradiation at 300--600{degree}C for up to 39 dpa produce substantial changes in the as-tempered microstructure of 9Cr-1MoVNb martensitic/ferritic steel. However, the changes in the dislocation/subgrain boundary and the precipitate structures caused by thermal aging or neutron irradiation are quite different in nature. During thermal aging, the as-tempered lath/subgrain boundary and carbide precipitate structures remain stable below 650{degree}C, but coarsen and recover somewhat at 650--704{degree}C. The formation of abundant intergranular Laves phase, intra-lath dislocation networks, and fine dispersions of VC needles are thermal aging effects that are superimposed upon the as-tempered microstructure at 482--593{degree}C. HFIR irradiation produces dense dispersions of very small black-dot'' dislocations loops at 300{degree}C and produces helium bubbles and voids at 400{degree}C At 300--500{degree}C, there is considerable recovery of the as-tempered lath/subgrain boundary structure and microstructural/microcompositional instability of the as-tempered carbide precipitates during irradiation. By contrast, the as-tempered microstructure remains essentially unchanged during irradiation at 600{degree}C. Comparison of thermally aged with irradiation material suggests that the instabilities of the as-tempered lath/subgrain boundary and precipitate structures at lower irradiation temperatures are radiation-induced effects, whereas the absence of both Laves phase and fine VC needles during irradiation is a radiation-retarded thermal effect.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6468768
- Report Number(s):
- CONF-900623-22; ON: DE91004516
- Country of Publication:
- United States
- Language:
- English
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AGING
ALLOYS
CHROMIUM-MOLYBDENUM STEELS
CRYSTAL STRUCTURE
DAMAGING NEUTRON FLUENCE
ELECTRON MICROSCOPY
ENRICHED URANIUM REACTORS
HFIR REACTOR
IRRADIATION REACTORS
ISOTOPE PRODUCTION REACTORS
MATERIALS
MATERIALS TESTING
MICROSCOPY
MICROSTRUCTURE
NEUTRON FLUENCE
NIOBIUM ALLOYS
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
REACTORS
RESEARCH AND TEST REACTORS
RESEARCH REACTORS
TANK TYPE REACTORS
TEMPERATURE EFFECTS
TEST REACTORS
TESTING
THERMAL REACTORS
THERMONUCLEAR REACTOR MATERIALS
TRANSMISSION ELECTRON MICROSCOPY
VANADIUM ALLOYS
WATER COOLED REACTORS
WATER MODERATED REACTORS