Direct Observation of an Austenite Memory Effect in Low-Alloy Steels

Abstract

Heating cycles around the civil-type γ→α transformation were performed in the photoemission electron microscope (PEEM) on a variety of low-carbon steels.On some of these alloysa powerful memory effect for the details of the austenitic structure was detected, in that the latter was faithfully reconstructed on reheating the transformed ferritic structure into the austenite range. When the ferrite was supercooled below a critical temperature, T_αcM, however, the memory effect was completely destroyed. This phenomenon was observed only in manganese-bearing alloys and did not depend on carbon or on carbide precipitation in the austenite. In addition, the results suggest that the memory effect exerts a control not only over the orientation of the γ-nuc1eiin a given ferrite region, but also on the extent of their subsequent growth.