Ledge mechanism of growth of colonies of discontinuous precipitate in austenite

Abstract

A ledge mechanism of growth of colonies of discontinuous vanadium carbide precipitate in an austenitic Fe-Mn-V-C alloy has been established by observing the progress of the reaction using scanning electron microscopy. The mobility of the risers of the ledges was measured and found to be at least an order of magnitude higher than that of the broad faces of the ledges. An explanation of this difference in mobility involving the nucleation of vanadium carbide has been proposed. Transmission electron microscopy of a ledged colony boundary confirmed that the planar density of coincident sites on the risers of ledges, where fibrous precipitation occurs, was greater than that on the broad faces at which particulate precipitation takes place.