Control of Nanostructues in Ultrahigh-Strength Steels
NORTHWESTERN UNIV EVANSTON IL
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The development of fine-scale multicomponent M2C carbides in AF1410 steel was observed as a function of time at the standard tempering temperature of 510C. Strong departures from equilibrium compositions are observed at early stages of precipitation, and carbide composition appears to be particle size dependent in a given microstructure. Analysis of the carbide composition trajectory during precipitation in terms of the thermodynamic contributions of coherency and capillarity indicates initial nucleation at compositions of reduced interfacial energy but reduced chemical driving force. The ability of multicomponent carbides to follow a precipitation composition trajectory of increasing interfacial energy and increasing driving force appears important to the maintenance of a fine particle size and high number density at late stages of precipitation for overaging resistance. Preliminary evidence is also found for predicted nonuniformity of the matrix composition in the stress field of a coherent particle.
- Metallurgy and Metallography