Abstract
It is well known that iron-chromium alloys are susceptible to phase separation within a low temperature miscibility gap and that this decomposition is deleterious to the mechanical properties of the material. This 475 [degree] embrittlement is of concern in commercial applications such as in the duplex stainless steel pipes that are used to carry the primary coolant water in nuclear power reactors. In these duplex stainless steels, the microstructure consists of austenite and 10 to 20% [delta]-ferrite. During service at a temperature of approximately 288 C, the ferrite phase of these steels undergoes spinodal decomposition and forms an iron-rich [alpha] phase and a chromium-enriched [alpha][prime] phase. Dislocations have difficulty in cutting through the complex interconnected morphology of these phases and therefore the hardness increases and the steel becomes embrittled. However, the effect of the presence of the austenite on the kinetics and morphology of the phases formed by spinodal decomposition is unclear. In this paper, the results of a combined transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM) investigation into the influence of retained austenite on the [alpha]-[alpha][prime] phase decomposition is presented. The material chosen for this investigation was a commercial Chromindur 2 magnetic material. This materialmore » has the advantages that it exhibits good contrast between the [alpha] and [alpha][prime] phases in both the transmission electron microscope and the field ion microscope and it does not have any other competing reactions such as the formation of ultrafine G-phase precipitates that occurs in some duplex stainless steels during low temperature aging.« less
Published Version
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