Low-temperature toughness of bcc Fe--Ni--Ti alloys
Thesis. The microstructural and kinetic factors controlling low- temperature toughness such as recrystallization, substructure, grain size, precipitation hardening, austenite formation, and retained austenite were systematically investigated on interstitial-free bcc Fe- Ni - Ti alloys. Among these factors, the grain size was found to be most influential. The enhancement of low-temperature toughness by controlling these microstructural factors was accomplished. As a result, a new cryogenic alloy with the extraordinary combination of strength and toughness was developed. The Fe--12Ni-0.5 Ti alloy has a yield stress of ~200 ksi and a V-notch impact energy of ~100 ft-lbs at -267 deg C (6 deg K). Up to this date, no comparable results have been reported. The effect of the grain size on the ductile-brittle transition temperature, T/sub c/, was also investigated. There exists a shift from a low grain size dependence on T/sub c/ to a high grain size dependence at grain size ~5 mu . When the grain size is reduced to less than 3 mu , thc ductile-brittle transition is suppressed to a lower temperature and does not appear even at temperatures very close to absolute zero. Hence, having the bcc structure in iron alloys is a necessary condition for the presence of the transition, but not a sufficient one. (auth)
- Research Organization:
- California Univ., Berkeley (USA). Lawrence Berkeley Lab.
- DOE Contract Number:
- W-7405-ENG-48
- NSA Number:
- NSA-29-004759
- OSTI ID:
- 4408698
- Report Number(s):
- LBL--1493
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
*NICKEL ALLOYS-- IMPACT STRENGTH
*TITANIUM ALLOYS-- IMPACT STRENGTH
AUSTENITE
BCC LATTICES
DUCTILE-BRITTLE TRANSITIONS
GRAIN SIZE
IMPACT SHOCK
N50230* --Metals
Ceramics
& Other Materials--Metals & Alloys--Properties
Structure & Phase Studies
PRECIPITATION HARDENING
RECRYSTALLIZATION
ULTRALOW TEMPERATURE
YIELD STRENGTH