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NANOPRECIPITATES IN STEELS

By Joachim H. Schneibel and Bimal K. Kad

Abstract

The creep strength of ferritic steels can be substantially improved by the incorporation of a high number density of nano-scale dispersoids. Examples for such alloys are the oxide dispersion strengthened steels MA956, MA957, and PM2000. The dispersoids in these steels contain Y and Ti, or Y and Al. They can be as small as a few nanometers in size. Processing is traditionally carried out by mechanical alloying of elemental or pre-alloyed powders mixed with Y2O3 powder. The goal of the present research is to identify alternative ways of producing ultrafine dispersoids. One possible way is internal oxidation, in which reactive elements dissolved in a metallic matrix are selectively oxidized. Internal oxidation experiments were carried out with Fe-Y, Fe-Ti-Y, and Fe-Al-Y precursors. Microstructural analysis showed that dispersoid dimensions as small as 10 nm could be achieved. Atomized Fe-0.25 at % Y powder was internally oxidized and consolidated by hot forging. An increase in the high-temperature creep strength by ~ 20 % was observed. Since it is likely that the composition of the precursor alloys is crucial for maximizing the number density and thermal stability of the oxides, experiments allowing the rapid screening of different compositions have been initiated

Year: 2011
OAI identifier: oai:CiteSeerX.psu:10.1.1.190.7289
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