Phase field modeling of the simultaneous formation of bainite and ferrite in TRIP steel

In transformation-induced plasticity (TRIP) steels, Si and/or Al delay cementite precipitation during bainite transformation leading to a transformation product that is usually referred to as carbide-free bainite. The present work proposes an approach to calibrate the parameters of a multi-phase field model to simulate the austenite decomposition into ferrite and bainite in a TRIP steel. Ferrite nuclei are introduced at austenite grain boundaries and suitable interfacial mobilities are selected to reproduce experimental ferrite formation kinetics. Bainite nucleation occurs for a sufficiently high undercooling at available interface sites (i.e. austenite grain boundaries, austenite-ferrite interfaces) and/or within austenite grains. For simplicity, the formation of carbide-free bainite is considered and a suitable anisotropy approach is proposed for the austenite-bainite interface mobility. The proposed model is benchmarked and validated with experimental continuous cooling transformation data. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.