Orientation of austenite reverted from martensite in Fe-2Mn-1.5Si-0.3C alloy

The orientation of austenite (gamma) reverted from lath martensite has been studied using electron back scatter diffraction (EBSD) in Fe-2%Mn-1.5%Si-03%C (mass%) alloy. Two morphologies of gamma, acicular and globular, are formed during reversion. Nucleation sites for acicular gamma are lath, block and sub-block boundaries, while those for globular gamma are prior gamma grain boundaries, as well as inside packets. Both acicular and globular gamma hold a near Kurdjumov-Sachs (K-S) orientation relationship with at least one of its surrounding tempered martensite blocks. Most acicular gamma have almost identical orientations with the prior gamma, while only a part of acicular gamma have a specific twin-related variant with the prior gamma. Furthermore, grain boundary globular gamma has almost identical orientations with the priory into which it does not grow. The formation of acicular and grain-boundary globular gamma was attributed to strong variant selection during gamma nucleation at lath, block and sub-block boundaries. On the other hand, orientation relationship analyses among intragranular globular gamma, tempered martensite and cementite suggest that the nucleation of gamma at cementite and tempered martensite interfaces causes weakening of the variant selection for the formation of intragranular globular gamma. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.