Digital Reconstruction of Engineered Austenite: Revisiting Effects of Grain Size and Ausforming on Variant Selection of Martensite

Abstract

In this work, the variant selection of martensite in a stainless maraging steel was investigated by electron backscattering diffraction and a new protocol of parent phase reconstruction. The reconstruction protocol enables digital austenite reversion into prior austenite microstructure and provides information of variant selection from a large number of austenite grains. It was found that strong variant selection occurred when the prior austenite grains were significantly refined in annealing or severely deformed by ausforming. When the prior austenite grain size was finer than 20 μm, it was found that a pair of twinned variants dominated in one packet, which dominates the prior austenite grain. This finding is explained by the inefficient space left by the early transformed martensite in the dominant packet. In contrast, variants with the same Bain orientation occupied most of the space of the austenite when the strain of the austenite exceeded 50%. The accumulated microbands on the 1 1 1 plane acted as nucleation sites of specific variants of martensite. This work provides statistical results to revisit the variant selection of martensitic transformation with the assistance of computational crystallography.