Morphological instability of δ-ferrite/γ-austenite interphase boundary in low carbon steels

The dynamic behavior of the delta-ferrite/gamma-austenite interphase boundary during delta/gamma transformations was observed in situ with a confocal scanning laser microscope. The morphological instability and the growth of the finger pattern of the delta/gamma interphase boundary were mainly focused on and studied in this work. It was found that the incoherent delta/gamma interphase boundaries were always unstable with finger-like morphology during delta-->gamma transformation, which developed along delta-GBs at low supercoolings (< 7 K) and even into the delta-matrix at higher supercoolings for the transformation. At the same time, the finger spacing was measured and analyzed by using the classical constitutional supercooling and instability theories, which show good agreement between the observations and theories. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.