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M: Metallphysik

M 12: Phasenumwandlungen II

M 12.4: Vortrag

Dienstag, 9. März 2004, 11:00–11:15, H16

Nucleation and Orientation Relationships during partial alpha-gamma-Phase Transformation in microalloyed Steels — •I. Lischewski, I. Lischewski, C.-M. Park, G. Gottstein, C.-M. Park, and G. Gottstein — Institut fuer Metallkunde und Metallphysik, RWTH Aachen, Kopernikusstr.14, D-52056 Aachen, Germany

The orientation relationships and the selection of crystallographic variants during partial ferrite to austenite transformation in a microalloyed steel were studied, to obtain new insights into the nucleation of this phase transformation. The samples were encased with a CrNi-18/9 steel foil and annealed at a low transformation temperature. Nickel, which diffused from the steel wrap into the transformed sample, stabilized the austenite nuclei.Therefore it was possible to establish a direct correspondence between prior ferrite and subsequent austenite crystallography. The local crystallography was measured by EBSD in a high resolution FEG-SEM. The austenite was observed to nucleate at random triple junctions of pre-existing ferrite grain boundaries and satisfied the K-S (Kurdjumov-Sachs) orientation relationship surprisingly, no apparent variant selection was observed during incipient stages of austenite nucleation. The preferential nucleation of austenite at random ferrite triple junctions was considered in a triple junction weighted orientation distribution which compared well with experimental results.