Research toward new alloys for generator retaining rings
The study was undertaken to develop an alloy suitable for use in the retaining rings of two-pole electrical generators which would have three key properties: (1) a yield strength of 1380 MPa (200 ksi) or greater with good residual toughness, (2) resistance to hydrogen embrittlement and stress-corrosion cracking, and (3) processability through heat treatment after hot forming, to avoid the necessity of cold forming of the ring. The principal alloy developed during the course of this work was an iron-based superalloy, designated EPRI-T, which has the nominal composition Fe-34.5Ni-5Cr-3Ti-3Ta-0.5Al-1.0Mo-0.3V-0.01B. The alloy is strengthened through the formation of cubic ..gamma..' precipitates of the composition Ni/sub 3/(Ti,Ta,Al). When given appropriate aging treatment from the as-forged condition, the alloy achieves yield strength in excess of 1380 MPa (200 ksi) with good residual toughness and promising resistance to cracking in gaseous hydrogen and salt water. The composition and processing of the alloy are the result of sequential metallurgical development, the steps of which are described. The alloy was chosen from a class of iron-based superalloys to achieve high strength in thick sections while maintaining reasonable costs, melting practice, and hot formability. The nickel content of the alloy was adjusted to insure that the alloy would be paramagnetic austenite after the aging reaction to form the Ni/sub 3/X strengthening precipitates. Tantalum was included among the ..gamma..'-forming elements to increase the lattice mismatch of the precipitate and improve alloy strength. Chromium was added to the composition to stabilize the austenite phase and eliminate stress-corrosion cracking susceptibility due to martensitic transformation of the austenite. The Mo-V-B group was included to inhibit integranular precipitation of the equilibrium eta phase and hence suppress a tendency toward intergranular fracture in the alloy.
- Research Organization:
- Lawrence Berkeley Lab., CA
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6544781
- Journal Information:
- Am. Soc. Test. Mater., Spec. Tech. Publ.; (United States), Journal Name: Am. Soc. Test. Mater., Spec. Tech. Publ.; (United States) Vol. 792; ISSN ASTTA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
200104* -- Fossil-Fueled Power Plants-- Components
36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
BORON
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
ELECTRIC GENERATORS
ELEMENTS
IRON ALLOYS
IRON BASE ALLOYS
MATERIALS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NICKEL ALLOYS
RESEARCH PROGRAMS
SEMIMETALS
TANTALUM ALLOYS
TITANIUM ALLOYS
VANADIUM ALLOYS