Precipitation hardening in Fe--Ni base austenitic alloys
The precipitation of metastable Ni/sub 3/X phases in the austenitic Fe--Ni-base alloys has been investigated by using various combinations of hardening elements, including Ti, Ta, Al, and Nb. The theoretical background on the formation of transition precipitates has been summarized based on: atomic size, compressibility, and electron/atom ratio. A model is proposed from an analysis of static concentration waves ordering the fcc lattice. Ordered structure of metastable precipitates will change from the triangularly ordered ..gamma..', to the rectangularly ordered ..gamma..'', as the atomic ratio (Ti + Al)/(Ta + Nb) decreases. The concurrent precipitation of ..gamma..' and ..gamma..'' occurs at 750/sup 0/C when the ratio is between 1.5 and 1.9. Aging behavior was studied over the temperature range of 500/sup 0/C to 900/sup 0/C. Typical hardness curves show a substantial hardening effect due to precipitation. A combination of strength and fracture toughness can be developed by employing double aging techniques. The growth of these coherent intermediate precipitates follows the power law with the aging time t : t/sup 1/3/ for the spherical ..gamma..' particles; and t/sup 1/2/ for the disc-shaped ..gamma..''. The equilibrium ..beta.. phase is observed to be able to nucleate on the surface of imbedded carbides. The addition of 5 wt % Cr to the age-hardened alloys provides a non-magnetic austenite which is stable against the formation of mechanically induced martensite.Cr addition retards aging kinetics of the precipitation reactions, and suppresses intergranular embrittlement caused by the high temperature solution anneal. The aging kinetics are also found to be influenced by solution annealing treatments.
- Research Organization:
- California Univ., Berkeley (USA). Lawrence Berkeley Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6233210
- Report Number(s):
- LBL-9208
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360101* -- Metals & Alloys-- Preparation & Fabrication
360102 -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
ANNEALING
AUSTENITE
CARBON ADDITIONS
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
DATA
DATA FORMS
EXPERIMENTAL DATA
FRACTURE PROPERTIES
HARDENING
HEAT TREATMENTS
INFORMATION
IRON ALLOYS
IRON BASE ALLOYS
MECHANICAL PROPERTIES
MOLYBDENUM ALLOYS
NICKEL ALLOYS
NICKEL STEELS
NICKEL-CHROMIUM STEELS
NIOBIUM ALLOYS
NUMERICAL DATA
PHASE TRANSFORMATIONS
PRECIPITATION HARDENING
STEELS
TABLES
TANTALUM ALLOYS
TENSILE PROPERTIES