Abstract
Case duplex stainless steels, used extensively in nuclear, chemical, and petroleum industries because of higher strength, better weldability, higher resistance to stress corrosion cracking, and soundness of casting, are susceptible to thermal aging embrittlement during service at temperatures as low as ∼250° C. Recent advances in understanding the aging mechanisms, kinetics, and mechanical properties are presented, with emphasis on application of the material in safety-significant components in a nuclear reactor. Aging embrittlement is primarily due to spinodal decomposition of ferrite involving segregation of Fe, Cr, and Ni, and precipitation of M 23C 6 on ferrite-austenite boundaries or in ferrite. Aging kinetics are strongly influenced by synergistic effects of other metallurgical reactions that occur in parallel with the spinodal decomposition, i.e. clustering of Ni, Mo, and Si and G-phase precipitation in ferrite. A number of methods are outlined for estimating end-of-life aging, depending on several factors such as degree of permissible conservatism, availability of component archive material, and methods of estimating and verifying the activation energy of aging.
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