Long-term-aging embrittlement of cast duplex stainless steels: Mechanism and kinetics
Microstructural characteristics of long-term-aged cast duplex stainless steel specimens including one from a BWR, have been investigated by SEM, TEM, SANS, and APFIM techniques. Three precipitate phases, Cr-rich ..cap alpha..' and the Ni- and Si-rich G phase, and ..gamma../sub 2/ austenite, have been identified in the ferrite matrix of the aged specimens. For CF-8 grade materials, M/sub 23/C/sub 6/ carbides were identified on the austenite-ferrite boundaries as well as in the ferrite matrix for aging at greater than or equal to450/sup 0/C. The Si, C, and Mo contents influenced the kinetics of the G-phase precipitation. However, TEM, and APFIM analyses indicate that the embrittlement during aging at less than or equal to400/sup 0/C is primarily associated with Fe and Cr segregation in ferrite by spinodal decomposition. For extended aging, e.g., 6-8 y at 350-400/sup 0/C, large platelike ..cap alpha..' formed by nucleation and growth from the structure produced by the spinodal decomposition. The Cr content appears to either promote the platelike ..cap alpha..' (high Cr content) or to suppress the ..cap alpha..' in favor of ..gamma../sub 2/ precipitation (low Cr). 21 refs., 10 figs., 2 tabs.
- Research Organization:
- Argonne National Lab., IL (USA)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5682948
- Report Number(s):
- CONF-871232-1; ON: DE88002929
- Country of Publication:
- United States
- Language:
- English
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36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
AGE HARDENING
ALLOYS
AUSTENITE
BWR TYPE REACTORS
CARBIDES
CARBON
CARBON ADDITIONS
CARBON COMPOUNDS
CHEMICAL REACTIONS
CHROMIUM
CHROMIUM ALLOYS
CORROSION
CORROSION RESISTANT ALLOYS
CRYSTAL STRUCTURE
ELEMENTS
EMBRITTLEMENT
FERRITE
HARDENING
HEAT TREATMENTS
IRON
IRON ALLOYS
IRON BASE ALLOYS
KINETICS
METALS
MICROSTRUCTURE
MOLYBDENUM
NICKEL
NONMETALS
PHASE TRANSFORMATIONS
REACTION KINETICS
REACTORS
SEGREGATION
SEMIMETALS
SILICON
STAINLESS STEELS
STEELS
STRESS CORROSION
TRANSITION ELEMENTS
WATER COOLED REACTORS
WATER MODERATED REACTORS